Shock heating and particle acceleration processes are some of the most fundamental physical phenomena of plasma physics with countless applications in laboratory physics, space physics, and astrophysics. This study is motivated by previous observations of non-thermal heating of heavy ions in astrophysical shocks (Korreck et al. 2004). Here, we focus on shocks driven by Interplanetary Coronal Mass Ejections (ICMEs) which heat the solar wind and accelerate particles. This study focuses specifically on the heating of heavy ions caused by these shocks. Previous studies have focused only on the two dynamically dominant species, H+ and He2+ . This study utilizes thermal properties measured by the Solar Wind Ion Composition Spectrometer (SWICS) aboard the Advanced Composition Explorer (ACE) spacecraft to examine heavy ion heating. This instrument provides data for many heavy ions not previously available for detailed study, such as Oxygen (O6+, O7+), Carbon (C5+, C6+), and Iron (Fe10+). The ion heating is found to depend critically on the upstream plasma
We measure the amount of absorption in the Lyman-alpha forest at 0 < z < 1.6 in HST FOS spectra of 74 QSOs. At 0 < z < 1.6 we find that 79% of the absorption is from the low density intergalactic medium, 12% from metals and 9% from the strong H I lines, nearly identical to the percentages (78, 15 and 7) that we measured independently at z=2 from spectra taken with the Kast spectrograph on the Lick 3-m. At z=1 the low density intergalactic medium absorbs 0.037 +/- 0.004 of the flux. The error includes some but not all of the uncertainty in the continuum level. The remaining part gives relative errors of approximately 0.21 when we report the mean absorption in eight independent redshift intervals, and 0.047 when we average over all redshifts. We find 1.46 times more absorption from the low density intergalactic medium than comes from Ly-alpha lines that Bechtold et al. 2002 listed in the same spectra. The amount of absorption increases with z and can be fit by a power law in (1+z) with index 1.01. This corresponds to no change in the number of lines, of fixed rest frame equivalent widths, per unit redshift, consistent with the Janknecht et al. 2006 results on the distribution of lines. When we include similar measurements from higher redshifts, we need more degrees of freedom to fit the amount of absorption at 0 < z < 3.2. A power law with a break in slope, changing from index 1.5 at low z to 3.0 above z ~ 1.1 is a better but only marginally acceptable fit. We also calculate two other continuous statistics, the flux probability distribution function and the flux autocorrelation function that is non zero out to v ~ 500 km/sec at 0.5 < z < 1.5.
We present a technique for creating a longitude-resolved image of Jupiter's thermal radio emission. The technique has been applied to VLA data taken on 25 January 1996 at a wavelength of 2 cm. A comparison with infrared data shows a good correlation between radio hot spots and the 5 micron hot spots seen on IRTF images. The brightest spot on the radio image is most likely the hot spot through which the Galileo probe entered Jupiter's atmosphere. We derived the ammonia abundance (= volume mixing ratio) in the hot spot, which is ~ 3 x 10^{-5}, about half that seen in longitude-averaged images of the NEB, or less than 1/3 of the longitude-averaged ammonia abundance in the EZ. This low ammonia abundance probably extends down to at least the 4 bar level.
We investigate the dynamical condensation process in a magnetized thermally bistable medium. We perform one-dimensional two fluid numerical simulations that describe the neutral and ionized components in the interstellar medium with purely transverse magnetic fields. We find that the cloud that is formed by the thermal instability always has magnetic field strength on the order of a few micro Gauss irrespective of the initial strength. This shows good agreement with the measurements of the magnetic field strength in diffuse clouds. We analytically show that the final magnetic field strength in the cloud that is formed as a consequence of the thermal instability is determined by the balance between ambipolar diffusion and accumulation of the magnetic field due to the condensation.
New narrow-band HAlpha imaging and subsequent optical spectra confirm G315.1+2.7, a previously identified candidate supernova remnant (SNR), as a bona-fide Galactic SNR. Present observations are based on independent discovery of filamentary optical emission nebulosity on images of the AAO/UKST HAlpha survey of the southern Galactic plane which were found to co-incide with existing multi-frequency radio detections. Separate medium and high dispersion spectra were taken across two locations of this 11 arcmin N-S aligned optical filament. The resulting spectral signatures were found to strongly confirm the SNR identification based on standard emission line ratio discriminators which characterise emission from shock heated gas. The average observed ratios of [SII]/HAlpha=1.13, [NII]/HAlpha=1.43 and [SII] 6717/6731=1.46, together with the simultaneous detection of [OII] at 3727A, [OIII] 5007A and [OI] 6300A, all point to an SNR origin of the observed optical emission. Careful scrutiny of the low-resolution but high sensitivity SHASSA HAlpha survey also revealed a low-level but distinct optical emission arc. This arc precisely correlates with the large, 2.5 degree, north-south angular extent of the proposed new SNR also seen as a fractured structure in the extant radio data. G315.1+2.7 was detected previously at 2400 and 4800 MHz and at 408 and 1420 MHz. We also identified associated radio emission at 843 MHz from the now publicly available SUMSS survey. On the basis of optical imaging and spectra and radio observations at five frequencies, we identify G315.1+2.7 as a new Galactic SNR. The large projected angular extent of the new remnant, together with the distance estimate of ~1.7 kpc and diameter of ~80pc, make G315.1+2.7 one of the largest remnants known.
We present high angular resolution radio snap-shot observations of seven nearby low-luminosity active galaxies (LLAGN) from the NUclei of GAlaxies (NUGA) survey. The observations were conducted with MERLIN and EVN/VLBI at 18cm and 6cm. At all observed angular resolutions and frequencies, we find indications for extended emission in about ~40% of the sources, consistent with the decrease of flux with increasing angular resolution. The extended components resemble jet emission in a majority of cases, consistent with the optically thin synchrotron emission implied by their steep spectra. We consider the compact 6cm EVN/VLBI radio emission of our sources in the context of the ``fundamental plane'' that previous LLAGN studies identified within the three-dimensional parameter space of radio luminosity, X-ray luminosity, and black hole mass. We demonstrate, using NGC7217 and NGC1068 as particular examples, that high-resolution, multi-epoch radio observations offer useful information about the origin of offsets from the fundamental plane.
The coincidence problem of late cosmic acceleration gets significantly alleviated when a suitable interaction between matter and dark energy, either of phantom type or not, enters the picture. We show that a class of models featuring this interaction fares rather well when contrasted with the anisotropies of the CMBR and the matter power spectrum. The latter test is very sensible to the interaction and may be used to discriminate between different models.
In the context of averaged cosmologies, the effective equations can be written in the form of "regional" Friedmannian equations with additional sources arising from the so-called backreaction of inhomogeneities. We propose a mean field description of this backreaction in terms of a regionally homogeneous scalar field: this provides a physical motivation to the phenomenological scalar fields generically called quintessence fields. We explicitly reconstruct the potential of the scalar field for a one-parameter family of scaling solutions to the backreaction problem, showing that it entails most of the standard scalar fields including e.g. standard and phantom quintessence scenarii.
Static spherically symmetric perfect fluid solutions are studied in metric $f(R)$ theories of gravity. We show that pressure and density do not uniquely determine $f(R)$ ie. given a matter distribution and an equation state, one cannot determine the functional form of $f(R)$. However, we also show that matching the outside Schwarzschild-de Sitter-metric to the metric inside the mass distribution leads to additional constraints that severely limit the allowed fluid configurations.
The puzzling phenomenon of pulsar kicks, i.e. the observed large escape velocities of pulsars out of supernova remnants, is examined for compact stars with a strange quark matter core. The direct Urca process in quark matter is studied in the presence of a strong magnetic field. Conditions for an asymmetric emission of the produced neutrinos are worked out in detail, giving constraints on the temperature, the strength of the magnetic field and the electron chemical potential in the quark matter core. In addition, the neutrino mean free paths for quark matter and a possible hadronic mantle are considered.
The mass-radius relation of compact stars is discussed with relation to the presence of quark matter in the core. The existence of a new family of compact stars with quark matter besides white dwarfs and ordinary neutron stars is outlined.
{We study in some details the statistical properties of the turbulent 2-phase interstellar atomic gas.{We present high resolution bidimensional numerical simulations of the interstellar atomic hydrogen which describe it over 3 to 4 orders of magnitude in spatial scales.}{The simulations produce naturally small scale structures having either large or small column density. It is tempting to propose that the former are connected to the tiny small scale structures observed in the ISM. We compute the mass spectrum of CNM structures and find that ${\cal N}(M) dM \propto M ^{-1.7} dM$, which is remarkably similar to the mass spectrum inferred for the CO clumps. We propose a theoretical explanation based on a formalism inspired from the Press & Schecter (1974) approach and used the fact that the turbulence within WNM is subsonic. This theory predicts ${\cal N}(M) \propto M ^{-5/3}$ in 2D and ${\cal N}(M) \propto M ^{-16/9}$ in 3D. We compute the velocity and the density power-spectra and conclude that, although the latter is rather flat, as observed in supersonic isothermal simulations, the former follows the Kolmogorov prediction and is dominated by its solenoidal component. This is due to the bistable nature of the flow which produces large density fluctuations even when the rms Mach number (of WNM) is not large. We also find that, whereas the energy at large scales is mainly in the WNM, at smaller scales, it is dominated by the kinetic energy of the CNM fragments.}
{It is necessary to understand the dynamics of the atomic gas to use complex modeling and to carry out detailed comparisons between theoretical models and observations.}{In a companion paper, we present high resolution bidimensional numerical simulations of the interstellar atomic hydrogen. Here, we further characterize these simulations and we compare our results with various observations.}{We give statistics of the column density and velocity along the line of sight and show that they compare favorably with observations of high-latitude lines of sight. We compute synthetic HI spectra and qualitatively discuss the information that could be inferred if these spectra were observed. Finally, we extract CNM clouds and study their physical properties finding strong similarities with real clouds. In particular, we find that the clouds follow Larson-type relations, i.e. $M \propto L^\gamma$, where $\gamma \simeq 1.7$ (we speculate that in 3D, $\gamma \simeq 2.5$) and $\sqrt{<\delta v^2>} \propto L^{0.4}$. We also find that the distribution, ${\cal N}(N)$, of the column density, $N$, of the CNM structures formed in the simulation follows ${\cal N}(N) \propto N^{-1.2}$ which is marginally compatible with the observational result obtained by Heiles & Troland (2005). From the mass-size relation and the mass spectrum, we derive an exponent for the column density distribution close to the value obtained in the numerical simulation.} {We conclude that the simulations reproduce various observational features reasonably well....}
We discuss the "basic" condition for an accreting neutron star to become a microquasar, i.e. ejecting relativistic particles orthogonal to the accretion disk instead of confining disk-material down to the magnetic poles and creating the two emitting caps typical for a X-ray pulsar. Jet creation is prevented for B >/= 10^12 G independent of the accretion rate. This excludes the possibility for a classic X-ray pulsar to develop a "microquasar-phase" and is consistent with the lack of radio emission from such pulsar systems. Millisecond accretion-powered pulsars, on the contrary, may show a "microquasar-phase", where B < 10^7.5 G is valid, whereas the limit for Z sources is B < 10^8.2 G. The implication of our analysis is that the jet might be the suitable agent of angular momentum sink for millisecond accretion-powered pulsars.
Many quasars and active galactic nuclei (AGN) appear in radio, optical, and
X-ray maps, as a bright nuclear sources from which emerge single or double
long, thin jets (Thomson et al., 1993). When observed with high angular
resolution these jets show structure with bright knots separated by relatively
dark regions. High percentages of polarization, sometimes more then 50% in some
objects, indicates the nonthermal nature of the radiation which is well
explained as the synchrotron radiation of the relativistic electrons in an
ordered magnetic field.
A strong collimation of jets is most probably connected with ordered magnetic
fields. The mechanism of magnetic collimation, first suggested by
Bisnovatyi-Kogan et al. (1969), was based on the initial charge separation,
leading to creation of oscillating electrical current, which produces azimuthal
magnetic field, preventing jet expansion and disappearance. Here we consider
magnetic collimation, connected with torsional oscillations of a cylinder with
elongated magnetic field. Instead of initial blobs with charge separation, we
consider a cylinder with a periodically distributed initial rotation around the
cylinder axis. The stabilizing azimuthal magnetic field is created here by
torsional oscillations, where charge separation is not necessary. Approximate
simplified model is developed. Ordinary differential equation is derived, and
solved numerically, what gives a possibility to estimate quantitatively the
range of parameters where jets may be stabilized by torsional oscillations.
In this work we explore the idea that the high frequency QPOs observed in
LMXBs may be explained as a resonant coupling between the neutron star spin and
epicyclic modes of accretion disk oscillations. We propose a new model for
these QPOs based on forced oscillations induced in the accretion disk due to a
stellar asymmetric rotating gravitational or magnetic field. It is shown that
particles evolving in a rotating non-axisymmetric field are subject to three
kinds of resonances: a corotation resonance, a Lindblad resonance due to a
driving force, and a parametric resonance due to the time varying epicyclic
frequencies. These results are extends by means of 2D numerical simulations of
a simplified version of the accretion disk. The simulations are performed for
the Newtonian gravitational potential, as well as for a pseudo-general
relativistic potential, which enables us to explore the behavior of the
resonances around both rotating neutron stars and black holes. Density
perturbations are only significant in the region located close to the inner
edge of the disk near the ISCO where the gravitational or magnetic perturbation
is maximal. It is argued that the nearly periodic motion induced in the disk
will produce high quality factor QPOs.
Finally, applying this model to a typical neutron star, we found that the
strongest response occurs when the frequency difference of the two modes equals
either the spin frequency (for "slow rotators") or half of it (for "fast
rotators"). The two main excited modes may both be connected to vertical
oscillations of the disk. We emphasize that strong gravity is not needed to
excite the modes.
A new scheme for testing the nuclear matter (NM) equation of state (EoS) at high densities using constraints from compact star (CS) phenomenology is applied to neutron stars with a core of deconfined quark matter (QM). An acceptable EoS shall not to be in conflict with the mass measurement of 2.1 +/- 0.2 solar mass (1 sigma level) for PSR J0751+1807 and the mass radius relation deduced from the thermal emission of RX J1856-3754. Further constraints for the state of matter in CS interiors come from temperature-age data for young, nearby objects. The CS cooling theory shall agree not only with these data, but also with the mass distribution inferred via population synthesis models as well as with LogN-LogS data. The scheme is applied to a set of hybrid EsoS with a phase transition to stiff, color superconducting QM which fulfills all above constraints and is constrained otherwise from NM saturation properties and flow data of heavy-ion collisions. We extrapolate our description to low temperatures and draw conclusions for the QCD phase diagram to be explored in heavy-ion collision experiments.
The properties of strangelets are reviewed and two experiments searching for them in cosmic rays are described. The prospects for strangelets as ultra-high energy cosmic rays beyond the classical GZK-cutoff are discussed.
Almost 40 years after the discovery of pulsars -- and despite a plethora of secured data on them -- pulsar theory is still beset by a number of fundamental inconsistencies. In this short contribution, I will argue that (i) magnetars do not exist, (ii) (ordinary) pulsars turnoff (or 'die') when their wind pressure falls short of keeping the CSM at a safe distance, exceeding 10^15 cm, whereupon they can mimic magnetars, (iii) msec pulsars are born fast (in core-collapse SNe), and are much older inside globular clusters than outside of them, (iv) neutron-star corotating magnetospheres can oscillate almost in resonance with their spin frequency, giving rise to pulse drifting, and to QPOs of accreting binary X-ray sources, and (v) the dying pulsars are the dominant sources of the cosmic rays, and of the GRBs.
In this review article the current status of particle dark matter is addressed. We discuss the main theoretical extensions of the standard model which allow to explain dark matter in terms of a (yet undiscovered) elementary particle. We then discuss the theoretical predictions for the searches of particle dark matter: direct detection in low background underground experiments and indirect detection of neutrinos, gamma-rays and antimatter with terrestrial and space-borne detectors. Attention will be placed also on the discussion of the uncertainties, mainly of astrophysical origin, which affect the theoretical predictions. The constraints placed by these searches on the extensions of the standard models will be briefly addressed.
We present a systematic analysis of all the BeppoSAX data of SGR 1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ~20 days after the August 1998 giant flare and during the 10^5 sec long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term softening only with a change of the temperature of a blackbody-like component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR 1900+14 persistent emission was significantly harder and possibly detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was ~25 % lower than the historical level, suggesting that the source was entering a quiescent period.
The soft gamma repeater (SGR) 1900+14 emitted the giant flare on 27 August 1998. Most gamma-ray detectors saturated during the initial spike of the giant flare because of the intense flux. However the plasma particle detector onboard GEOTAIL observed the first 300 ms time profile with a time resolution of 5.577 ms and the initial spike of the giant flare was first resolved. The time profile shows some similarities to that of the SGR 1806-20 giant flare in 2004: the clear exponential decay and the small hump in the decay phase around 300 or 400 ms.
Both superbursters and soft X-ray transients probe the thermal structure of the crust on compact stars and are sensitive to the process of deep crustal heating. It was recently shown that the transfer of matter from crust to core in a strange star can heat the crust by deconfinement and ignite superbursts provided certain constraints on the strange quark matter equation of state are fulfilled. Corresponding constraints are derived for soft X-ray transients in a simple parameterized model assuming their quiescent emission is powered in the same way, and the time dependence of this heating mechanism in transient systems is discussed.
We have performed an analysis and interpretation of the X-ray light curve of the accreting neutron star Her X-1 obtained with the ASM RXTE over the period 1996 February to 2004 September. The averaged X-ray light curves are constructed by means of adding up light curves corresponding to different 35 day cycles. A numerical model is introduced to explain the properties of the averaged light curves. We argue that a change of the tilt of the accretion disk over the 35 day period is necessary to account for the observed features and show that our numerical model can explain such a behavior of the disk and reproduce the details of the light curve.
We present model spectra and lightcurves of thermal emission from hot spots on the surface of a compact star with an unmagnetized light-element atmosphere. An application to X-ray observations of the nearest known rotation-powered millisecond pulsar (MSP) PSR J0437--4715 reveals that the thermal emission from this pulsar is fully consistent with such a model, enabling constraints on important properties of the underlying neutron star. We demonstrate that the observed thermal X-ray pulsations from J0437--4715 are incompatible with blackbody emission and require the presence of a limb-darkened, light element (most likely hydrogen) atmosphere on the neutron star surface. The morphology of the X-ray pulse profile is consistent with a global dipole configuration of the pulsar magnetic field but suggests an off-center magnetic axis, with a displacement of $\gtrsim$1 km from the stellar center. For an assumed mass of 1.4 M$_{\odot}$, the model restricts the allowed stellar radii to R=6.8-13.8 km (90% confidence) and R>6.7 km (99.9% confidence), which is consistent with standard NS equations of state and rules out an ultra-compact star. Deeper spectroscopic and timing observations of this and other nearby radio MSPs with current and future X-ray facilities (e.g., Constellation-X and XEUS) can provide further insight into the fundamental properties of neutron stars.
Shock heating and particle acceleration processes are some of the most fundamental physical phenomena of plasma physics with countless applications in laboratory physics, space physics, and astrophysics. This study is motivated by previous observations of non-thermal heating of heavy ions in astrophysical shocks (Korreck et al. 2004). Here, we focus on shocks driven by Interplanetary Coronal Mass Ejections (ICMEs) which heat the solar wind and accelerate particles. This study focuses specifically on the heating of heavy ions caused by these shocks. Previous studies have focused only on the two dynamically dominant species, H+ and He2+ . This study utilizes thermal properties measured by the Solar Wind Ion Composition Spectrometer (SWICS) aboard the Advanced Composition Explorer (ACE) spacecraft to examine heavy ion heating. This instrument provides data for many heavy ions not previously available for detailed study, such as Oxygen (O6+, O7+), Carbon (C5+, C6+), and Iron (Fe10+). The ion heating is found to depend critically on the upstream plasma
We measure the amount of absorption in the Lyman-alpha forest at 0 < z < 1.6 in HST FOS spectra of 74 QSOs. At 0 < z < 1.6 we find that 79% of the absorption is from the low density intergalactic medium, 12% from metals and 9% from the strong H I lines, nearly identical to the percentages (78, 15 and 7) that we measured independently at z=2 from spectra taken with the Kast spectrograph on the Lick 3-m. At z=1 the low density intergalactic medium absorbs 0.037 +/- 0.004 of the flux. The error includes some but not all of the uncertainty in the continuum level. The remaining part gives relative errors of approximately 0.21 when we report the mean absorption in eight independent redshift intervals, and 0.047 when we average over all redshifts. We find 1.46 times more absorption from the low density intergalactic medium than comes from Ly-alpha lines that Bechtold et al. 2002 listed in the same spectra. The amount of absorption increases with z and can be fit by a power law in (1+z) with index 1.01. This corresponds to no change in the number of lines, of fixed rest frame equivalent widths, per unit redshift, consistent with the Janknecht et al. 2006 results on the distribution of lines. When we include similar measurements from higher redshifts, we need more degrees of freedom to fit the amount of absorption at 0 < z < 3.2. A power law with a break in slope, changing from index 1.5 at low z to 3.0 above z ~ 1.1 is a better but only marginally acceptable fit. We also calculate two other continuous statistics, the flux probability distribution function and the flux autocorrelation function that is non zero out to v ~ 500 km/sec at 0.5 < z < 1.5.
We present a technique for creating a longitude-resolved image of Jupiter's thermal radio emission. The technique has been applied to VLA data taken on 25 January 1996 at a wavelength of 2 cm. A comparison with infrared data shows a good correlation between radio hot spots and the 5 micron hot spots seen on IRTF images. The brightest spot on the radio image is most likely the hot spot through which the Galileo probe entered Jupiter's atmosphere. We derived the ammonia abundance (= volume mixing ratio) in the hot spot, which is ~ 3 x 10^{-5}, about half that seen in longitude-averaged images of the NEB, or less than 1/3 of the longitude-averaged ammonia abundance in the EZ. This low ammonia abundance probably extends down to at least the 4 bar level.
We investigate the dynamical condensation process in a magnetized thermally bistable medium. We perform one-dimensional two fluid numerical simulations that describe the neutral and ionized components in the interstellar medium with purely transverse magnetic fields. We find that the cloud that is formed by the thermal instability always has magnetic field strength on the order of a few micro Gauss irrespective of the initial strength. This shows good agreement with the measurements of the magnetic field strength in diffuse clouds. We analytically show that the final magnetic field strength in the cloud that is formed as a consequence of the thermal instability is determined by the balance between ambipolar diffusion and accumulation of the magnetic field due to the condensation.
New narrow-band HAlpha imaging and subsequent optical spectra confirm G315.1+2.7, a previously identified candidate supernova remnant (SNR), as a bona-fide Galactic SNR. Present observations are based on independent discovery of filamentary optical emission nebulosity on images of the AAO/UKST HAlpha survey of the southern Galactic plane which were found to co-incide with existing multi-frequency radio detections. Separate medium and high dispersion spectra were taken across two locations of this 11 arcmin N-S aligned optical filament. The resulting spectral signatures were found to strongly confirm the SNR identification based on standard emission line ratio discriminators which characterise emission from shock heated gas. The average observed ratios of [SII]/HAlpha=1.13, [NII]/HAlpha=1.43 and [SII] 6717/6731=1.46, together with the simultaneous detection of [OII] at 3727A, [OIII] 5007A and [OI] 6300A, all point to an SNR origin of the observed optical emission. Careful scrutiny of the low-resolution but high sensitivity SHASSA HAlpha survey also revealed a low-level but distinct optical emission arc. This arc precisely correlates with the large, 2.5 degree, north-south angular extent of the proposed new SNR also seen as a fractured structure in the extant radio data. G315.1+2.7 was detected previously at 2400 and 4800 MHz and at 408 and 1420 MHz. We also identified associated radio emission at 843 MHz from the now publicly available SUMSS survey. On the basis of optical imaging and spectra and radio observations at five frequencies, we identify G315.1+2.7 as a new Galactic SNR. The large projected angular extent of the new remnant, together with the distance estimate of ~1.7 kpc and diameter of ~80pc, make G315.1+2.7 one of the largest remnants known.
We present high angular resolution radio snap-shot observations of seven nearby low-luminosity active galaxies (LLAGN) from the NUclei of GAlaxies (NUGA) survey. The observations were conducted with MERLIN and EVN/VLBI at 18cm and 6cm. At all observed angular resolutions and frequencies, we find indications for extended emission in about ~40% of the sources, consistent with the decrease of flux with increasing angular resolution. The extended components resemble jet emission in a majority of cases, consistent with the optically thin synchrotron emission implied by their steep spectra. We consider the compact 6cm EVN/VLBI radio emission of our sources in the context of the ``fundamental plane'' that previous LLAGN studies identified within the three-dimensional parameter space of radio luminosity, X-ray luminosity, and black hole mass. We demonstrate, using NGC7217 and NGC1068 as particular examples, that high-resolution, multi-epoch radio observations offer useful information about the origin of offsets from the fundamental plane.
The coincidence problem of late cosmic acceleration gets significantly alleviated when a suitable interaction between matter and dark energy, either of phantom type or not, enters the picture. We show that a class of models featuring this interaction fares rather well when contrasted with the anisotropies of the CMBR and the matter power spectrum. The latter test is very sensible to the interaction and may be used to discriminate between different models.
In the context of averaged cosmologies, the effective equations can be written in the form of "regional" Friedmannian equations with additional sources arising from the so-called backreaction of inhomogeneities. We propose a mean field description of this backreaction in terms of a regionally homogeneous scalar field: this provides a physical motivation to the phenomenological scalar fields generically called quintessence fields. We explicitly reconstruct the potential of the scalar field for a one-parameter family of scaling solutions to the backreaction problem, showing that it entails most of the standard scalar fields including e.g. standard and phantom quintessence scenarii.
Static spherically symmetric perfect fluid solutions are studied in metric $f(R)$ theories of gravity. We show that pressure and density do not uniquely determine $f(R)$ ie. given a matter distribution and an equation state, one cannot determine the functional form of $f(R)$. However, we also show that matching the outside Schwarzschild-de Sitter-metric to the metric inside the mass distribution leads to additional constraints that severely limit the allowed fluid configurations.
The puzzling phenomenon of pulsar kicks, i.e. the observed large escape velocities of pulsars out of supernova remnants, is examined for compact stars with a strange quark matter core. The direct Urca process in quark matter is studied in the presence of a strong magnetic field. Conditions for an asymmetric emission of the produced neutrinos are worked out in detail, giving constraints on the temperature, the strength of the magnetic field and the electron chemical potential in the quark matter core. In addition, the neutrino mean free paths for quark matter and a possible hadronic mantle are considered.
The mass-radius relation of compact stars is discussed with relation to the presence of quark matter in the core. The existence of a new family of compact stars with quark matter besides white dwarfs and ordinary neutron stars is outlined.
{We study in some details the statistical properties of the turbulent 2-phase interstellar atomic gas.{We present high resolution bidimensional numerical simulations of the interstellar atomic hydrogen which describe it over 3 to 4 orders of magnitude in spatial scales.}{The simulations produce naturally small scale structures having either large or small column density. It is tempting to propose that the former are connected to the tiny small scale structures observed in the ISM. We compute the mass spectrum of CNM structures and find that ${\cal N}(M) dM \propto M ^{-1.7} dM$, which is remarkably similar to the mass spectrum inferred for the CO clumps. We propose a theoretical explanation based on a formalism inspired from the Press & Schecter (1974) approach and used the fact that the turbulence within WNM is subsonic. This theory predicts ${\cal N}(M) \propto M ^{-5/3}$ in 2D and ${\cal N}(M) \propto M ^{-16/9}$ in 3D. We compute the velocity and the density power-spectra and conclude that, although the latter is rather flat, as observed in supersonic isothermal simulations, the former follows the Kolmogorov prediction and is dominated by its solenoidal component. This is due to the bistable nature of the flow which produces large density fluctuations even when the rms Mach number (of WNM) is not large. We also find that, whereas the energy at large scales is mainly in the WNM, at smaller scales, it is dominated by the kinetic energy of the CNM fragments.}
{It is necessary to understand the dynamics of the atomic gas to use complex modeling and to carry out detailed comparisons between theoretical models and observations.}{In a companion paper, we present high resolution bidimensional numerical simulations of the interstellar atomic hydrogen. Here, we further characterize these simulations and we compare our results with various observations.}{We give statistics of the column density and velocity along the line of sight and show that they compare favorably with observations of high-latitude lines of sight. We compute synthetic HI spectra and qualitatively discuss the information that could be inferred if these spectra were observed. Finally, we extract CNM clouds and study their physical properties finding strong similarities with real clouds. In particular, we find that the clouds follow Larson-type relations, i.e. $M \propto L^\gamma$, where $\gamma \simeq 1.7$ (we speculate that in 3D, $\gamma \simeq 2.5$) and $\sqrt{<\delta v^2>} \propto L^{0.4}$. We also find that the distribution, ${\cal N}(N)$, of the column density, $N$, of the CNM structures formed in the simulation follows ${\cal N}(N) \propto N^{-1.2}$ which is marginally compatible with the observational result obtained by Heiles & Troland (2005). From the mass-size relation and the mass spectrum, we derive an exponent for the column density distribution close to the value obtained in the numerical simulation.} {We conclude that the simulations reproduce various observational features reasonably well....}
We discuss the "basic" condition for an accreting neutron star to become a microquasar, i.e. ejecting relativistic particles orthogonal to the accretion disk instead of confining disk-material down to the magnetic poles and creating the two emitting caps typical for a X-ray pulsar. Jet creation is prevented for B >/= 10^12 G independent of the accretion rate. This excludes the possibility for a classic X-ray pulsar to develop a "microquasar-phase" and is consistent with the lack of radio emission from such pulsar systems. Millisecond accretion-powered pulsars, on the contrary, may show a "microquasar-phase", where B < 10^7.5 G is valid, whereas the limit for Z sources is B < 10^8.2 G. The implication of our analysis is that the jet might be the suitable agent of angular momentum sink for millisecond accretion-powered pulsars.
Many quasars and active galactic nuclei (AGN) appear in radio, optical, and
X-ray maps, as a bright nuclear sources from which emerge single or double
long, thin jets (Thomson et al., 1993). When observed with high angular
resolution these jets show structure with bright knots separated by relatively
dark regions. High percentages of polarization, sometimes more then 50% in some
objects, indicates the nonthermal nature of the radiation which is well
explained as the synchrotron radiation of the relativistic electrons in an
ordered magnetic field.
A strong collimation of jets is most probably connected with ordered magnetic
fields. The mechanism of magnetic collimation, first suggested by
Bisnovatyi-Kogan et al. (1969), was based on the initial charge separation,
leading to creation of oscillating electrical current, which produces azimuthal
magnetic field, preventing jet expansion and disappearance. Here we consider
magnetic collimation, connected with torsional oscillations of a cylinder with
elongated magnetic field. Instead of initial blobs with charge separation, we
consider a cylinder with a periodically distributed initial rotation around the
cylinder axis. The stabilizing azimuthal magnetic field is created here by
torsional oscillations, where charge separation is not necessary. Approximate
simplified model is developed. Ordinary differential equation is derived, and
solved numerically, what gives a possibility to estimate quantitatively the
range of parameters where jets may be stabilized by torsional oscillations.
In this work we explore the idea that the high frequency QPOs observed in
LMXBs may be explained as a resonant coupling between the neutron star spin and
epicyclic modes of accretion disk oscillations. We propose a new model for
these QPOs based on forced oscillations induced in the accretion disk due to a
stellar asymmetric rotating gravitational or magnetic field. It is shown that
particles evolving in a rotating non-axisymmetric field are subject to three
kinds of resonances: a corotation resonance, a Lindblad resonance due to a
driving force, and a parametric resonance due to the time varying epicyclic
frequencies. These results are extends by means of 2D numerical simulations of
a simplified version of the accretion disk. The simulations are performed for
the Newtonian gravitational potential, as well as for a pseudo-general
relativistic potential, which enables us to explore the behavior of the
resonances around both rotating neutron stars and black holes. Density
perturbations are only significant in the region located close to the inner
edge of the disk near the ISCO where the gravitational or magnetic perturbation
is maximal. It is argued that the nearly periodic motion induced in the disk
will produce high quality factor QPOs.
Finally, applying this model to a typical neutron star, we found that the
strongest response occurs when the frequency difference of the two modes equals
either the spin frequency (for "slow rotators") or half of it (for "fast
rotators"). The two main excited modes may both be connected to vertical
oscillations of the disk. We emphasize that strong gravity is not needed to
excite the modes.
A new scheme for testing the nuclear matter (NM) equation of state (EoS) at high densities using constraints from compact star (CS) phenomenology is applied to neutron stars with a core of deconfined quark matter (QM). An acceptable EoS shall not to be in conflict with the mass measurement of 2.1 +/- 0.2 solar mass (1 sigma level) for PSR J0751+1807 and the mass radius relation deduced from the thermal emission of RX J1856-3754. Further constraints for the state of matter in CS interiors come from temperature-age data for young, nearby objects. The CS cooling theory shall agree not only with these data, but also with the mass distribution inferred via population synthesis models as well as with LogN-LogS data. The scheme is applied to a set of hybrid EsoS with a phase transition to stiff, color superconducting QM which fulfills all above constraints and is constrained otherwise from NM saturation properties and flow data of heavy-ion collisions. We extrapolate our description to low temperatures and draw conclusions for the QCD phase diagram to be explored in heavy-ion collision experiments.
The properties of strangelets are reviewed and two experiments searching for them in cosmic rays are described. The prospects for strangelets as ultra-high energy cosmic rays beyond the classical GZK-cutoff are discussed.
Almost 40 years after the discovery of pulsars -- and despite a plethora of secured data on them -- pulsar theory is still beset by a number of fundamental inconsistencies. In this short contribution, I will argue that (i) magnetars do not exist, (ii) (ordinary) pulsars turnoff (or 'die') when their wind pressure falls short of keeping the CSM at a safe distance, exceeding 10^15 cm, whereupon they can mimic magnetars, (iii) msec pulsars are born fast (in core-collapse SNe), and are much older inside globular clusters than outside of them, (iv) neutron-star corotating magnetospheres can oscillate almost in resonance with their spin frequency, giving rise to pulse drifting, and to QPOs of accreting binary X-ray sources, and (v) the dying pulsars are the dominant sources of the cosmic rays, and of the GRBs.
In this review article the current status of particle dark matter is addressed. We discuss the main theoretical extensions of the standard model which allow to explain dark matter in terms of a (yet undiscovered) elementary particle. We then discuss the theoretical predictions for the searches of particle dark matter: direct detection in low background underground experiments and indirect detection of neutrinos, gamma-rays and antimatter with terrestrial and space-borne detectors. Attention will be placed also on the discussion of the uncertainties, mainly of astrophysical origin, which affect the theoretical predictions. The constraints placed by these searches on the extensions of the standard models will be briefly addressed.
We present a systematic analysis of all the BeppoSAX data of SGR 1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ~20 days after the August 1998 giant flare and during the 10^5 sec long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term softening only with a change of the temperature of a blackbody-like component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR 1900+14 persistent emission was significantly harder and possibly detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was ~25 % lower than the historical level, suggesting that the source was entering a quiescent period.
The soft gamma repeater (SGR) 1900+14 emitted the giant flare on 27 August 1998. Most gamma-ray detectors saturated during the initial spike of the giant flare because of the intense flux. However the plasma particle detector onboard GEOTAIL observed the first 300 ms time profile with a time resolution of 5.577 ms and the initial spike of the giant flare was first resolved. The time profile shows some similarities to that of the SGR 1806-20 giant flare in 2004: the clear exponential decay and the small hump in the decay phase around 300 or 400 ms.
Both superbursters and soft X-ray transients probe the thermal structure of the crust on compact stars and are sensitive to the process of deep crustal heating. It was recently shown that the transfer of matter from crust to core in a strange star can heat the crust by deconfinement and ignite superbursts provided certain constraints on the strange quark matter equation of state are fulfilled. Corresponding constraints are derived for soft X-ray transients in a simple parameterized model assuming their quiescent emission is powered in the same way, and the time dependence of this heating mechanism in transient systems is discussed.
We have performed an analysis and interpretation of the X-ray light curve of the accreting neutron star Her X-1 obtained with the ASM RXTE over the period 1996 February to 2004 September. The averaged X-ray light curves are constructed by means of adding up light curves corresponding to different 35 day cycles. A numerical model is introduced to explain the properties of the averaged light curves. We argue that a change of the tilt of the accretion disk over the 35 day period is necessary to account for the observed features and show that our numerical model can explain such a behavior of the disk and reproduce the details of the light curve.
We present model spectra and lightcurves of thermal emission from hot spots on the surface of a compact star with an unmagnetized light-element atmosphere. An application to X-ray observations of the nearest known rotation-powered millisecond pulsar (MSP) PSR J0437--4715 reveals that the thermal emission from this pulsar is fully consistent with such a model, enabling constraints on important properties of the underlying neutron star. We demonstrate that the observed thermal X-ray pulsations from J0437--4715 are incompatible with blackbody emission and require the presence of a limb-darkened, light element (most likely hydrogen) atmosphere on the neutron star surface. The morphology of the X-ray pulse profile is consistent with a global dipole configuration of the pulsar magnetic field but suggests an off-center magnetic axis, with a displacement of $\gtrsim$1 km from the stellar center. For an assumed mass of 1.4 M$_{\odot}$, the model restricts the allowed stellar radii to R=6.8-13.8 km (90% confidence) and R>6.7 km (99.9% confidence), which is consistent with standard NS equations of state and rules out an ultra-compact star. Deeper spectroscopic and timing observations of this and other nearby radio MSPs with current and future X-ray facilities (e.g., Constellation-X and XEUS) can provide further insight into the fundamental properties of neutron stars.
The backreaction of the Lorentz force on the alpha-effect is studied in the limit of small magnetic and fluid Reynolds numbers, using the first order smoothing approximation (FOSA) to solve both the induction and momentum equations. Both steady and time dependent forcings are considered. In the low Reynolds number limit, the velocity and magnetic fields can be expressed explicitly in terms of the forcing function. The nonlinear alpha-effect is then shown to be expressible in several equivalent forms in agreement with formalisms that are used in various closure schemes. On the one hand, one can express alpha completely in terms of the helical properties of the velocity field as in traditional FOSA, or, alternatively, as the sum of two terms, a so-called kinetic alpha-effect and an oppositely signed term proportional to the helical part of the small scale magnetic field. The latter alternative is similar to the formulation in other closure schemes (abridged).
The production of runaway massive binaries offers key insights into the evolution of close binary stars and open clusters. The stars HD 14633 and HD 15137 are rare examples of such runaway systems, and in this work we investigate the mechanism by which they were ejected from their parent open cluster, NGC 654. We discuss observational characteristics that can be used to distinguish supernova ejected systems from those ejected by dynamical interactions, and we present the results of a new radio pulsar search of these systems as well as estimates of their predicted X-ray flux assuming that each binary contains a compact object. Since neither pulsars nor X-ray emission are observed in these systems, we cannot conclude that these binaries contain compact companions. We also consider whether they may have been ejected by dynamical interactions in the dense environment where they formed, and our simulations of four-body interactions suggest that a dynamical origin is possible but unlikely. We recommend further X-ray observations that will conclusively identify whether HD 14633 or HD 15137 contain neutron stars.
We study the planet populations in the discovery window of the
CoRoT-space-telescope scheduled for launch on December 27th. We base the
prediction on `first principles' calculations of planet formation in the
framework of the planetesimal hypothesis.
Aims: To provide a-priori planetary initial mass functions for confrontation
with the CoRoT-planet discoveries in the entire range of sensitivity of the
CoRoT instrument, i.e. for all giant planets and down to terrestrial planet
masses.
Methods: We construct a comprehensive set of static complete-equilibrium
core-envelope protoplanets with detailed equations of state and opacity and
radiative transfer by convection and radiation. Protoplanets are calculated for
host-star masses of 0.8 to 2 solar masses and orbital periods of 1 to 16 days.
We subsequently check the stability of the planetary population by a series of
methods.
Results: We find the static planetary populations to be stable and thus a
plausible ensemble to predict the planetary IMF for orbital periods in the
specified range.
Conclusions: We predict bimodal planetary initial mass functions with shapes
depending on orbital period. The two main maxima are around a Jupiter mass and
about 50 earth masses. We predict an abundant population of Hot Neptunes and a
large population of planets that fill the solar-system gap of planetary masses
between Neptune and Saturn.
We review the contribution of extra galactic inspiralling double neutron stars, to the LISA astrophysical gravitational wave foreground. Using recent fits of the star formation rate, we show that sources beyond $z_*=0.005$ contribute to a truly continuous background, which may dominate the LISA instrumental noise in the range $3 \simeq 10^{-4}$ - $1 \times 10^{-2}$ Hz and overwhelm the galactic WD-WD confusion noise at frequencies larger than $\nu_o \simeq 2\times 10^{-3}$.
We report on the relative optical variability of the three brightest nearby quasars, 3C 273, PDS 456, and PHL 1811. All three have comparable absolute magnitudes, but PDS 456 and PHL 1811 are radio quiet. PDS 456 is a broad-line object, but PHL 1811 could be classified as a high-luminosity Narrow-Line Seyfert 1 (NLS1). Both of the radio-quiet quasars show significant variability on a timescale of a few days. The seasonal rms V-band variability amplitudes of 3C 273 and PDS 456 are indistinguishable, and the seasonal rms variability amplitude of PHL 1811 was only exceeded by 3C 273 once in 30 years of monitoring. We find no evidence that the optical variability of 3C 273 is greater than or more rapid than the variability of the comparably-bright, radio-quiet quasars. This suggests that not only do radio-loud and radio-quiet AGNs have similar spectral energy distributions, but that the variability mechanisms are also similar. The optical variability of 3C 273 is not dominated by a "blazer" component.
The conformal invariance of the Einstein field equations allows one to model hadrons as "strong gravity" black holes if one uses appropriate scaling of units and a revised gravitational coupling factor. The inner consistency of this hypothesis is demonstrated by deriving the mass of the proton from an equation that relates the angular momentum and mass of a Kerr-Newman black hole. The radius of a helium nucleus is derived in a second test.
The massive black holes in most faint active galactic nuclei (AGNs) and even normal galaxies are still accreting gases, though their accretion rates are very low. Radiatively inefficient accretion flows (RIAFs) are supposed in these faint sources, which should radiate mostly in the hard X-ray band. We calculate the contribution to the X-ray background from both the bright AGNs and the RIAFs in faint AGNs/normal galaxies. Our calculations show that both the observed intensity and spectral shape of the XRB with an energy peak at ~30$ keV can be well reproduced without including the emission of Compton-thick AGNs, if the massive black holes in faint AGNs/normal galaxies are spinning rapidly with a~0.9 and accreting at rates ~1.0-3.0\times 10^{-4}. It indicates that less than ~5 per cent of local massive black hole mass density was accreted during radiatively inefficient accretion phases, which is obviously only an upper limit, because Compton-thick AGNs have not been considered. If the same number of the Compton-thick AGNs with log N_H=24-25 as those with log N_H=23-24 is considered, the fraction of local black hole mass density accumulated during inefficient accretion phases should be lower than ~2 per cent.
I present new comparisons of AGN optical, UV, and X-ray variations. These reveal complex relationships between the different passbands that can change with time in a given object. While there is evidence from several objects that X-ray and optical activity levels are correlated on long timescales, variations on shorter timescales can occur independently. It is proposed that the combination of correlated and uncorrelated short-timescale variability is a consequence of anisotropic high-energy emission. It is also argued that the correlation between X-ray and optical variability on long timescales must be due to a common underlying factor and not to reprocessing of X-ray radiation.
Based on quintessence models with anti-correlation between the quintessence fluctuations and adiabatic perturbations in the other matter components, we show that if the quintessence potential is sufficiently steep at the end of inflation, the quintessence fluctuations can be large enough to sufficiently suppress the CMB power spectrum at low multipoles without excess gravitational waves. The leaping kinetic term quintessence and the crossover quintessence models, can realize such steep potential at the end of inflation, and therefore can give rise to a low CMB quadrupole as required by observations.
The first results from a near-contemporaneous optical and infrared spectroscopic observing program designed to probe the detailed density structure of classical Be circumstellar disks are presented. We report the discovery of asymmetrical infrared emission lines of He I, O I, Fe II, and the Brackett, Paschen, and Pfund series lines of H I which exhibit an opposite V/R orientation (V $>$ R) to that observed for the optical Balmer H$\alpha$ line (V $<$ R) in the classical Be star $\zeta$ Tau. We interpret these data as evidence that the density wave which characterizes $\zeta$ Tau's disk has a significantly different average azimuthal morphology in the inner disk region as compared to the outer disk region. A follow-up multi-wavelength observational campaign to trace the temporal evolution of these line profile morphologies, along with detailed theoretical modeling, is suggested to test this hypothesis.
We compare N-body simulations of isolated galaxies performed in both frameworks of modified Newtonian dynamics (MOND) and Newtonian gravity with dark matter (DM). We have developed a multigrid code able to efficiently solve the modified Poisson equation derived from the Lagrangian formalism AQUAL. We take particular care of the boundary conditions that are a crucial point in MOND. The 3-dimensional dynamics of initially identical stellar discs is studied in both models. In Newtonian gravity the live DM halo is chosen to fit the rotation curve of the MOND galaxy. For the same value of the Toomre parameter (Q_T), galactic discs in MOND develop a bar instability sooner than in the DM model. In a second phase the MOND bars weaken while the DM bars continue to grow by exchanging angular momentum with the halo. The bar pattern speed evolves quite differently in the two models: there is no dynamical friction on the MOND bars so they keep a constant pattern speed while the DM bars slow down significantly. This affects the position of resonance like the corotation and the peanut. The peanut lobes in the DM model move radially outward while they keep the same position in MOND. Simulations of (only stellar) galaxies of different types on the Hubble sequence lead to a statistical bar frequency that is closer to observations for the MOND than the DM model.
Using cosmological hydrodynamic simulations we measure the mean transmitted flux in the Lyman alpha forest for quasar sightlines that pass near a foreground quasar. We find that the trend of absorption with pixel-quasar separation distance can be fitted using a simple power law form including the usual correlation function parameters r_{0} and \gamma so that (<F(r)> = \sum exp(-tau_eff*(1+(r/r_{0})^(-\gamma)))). From the simulations we find the relation between r_{0} and quasar mass and formulate this as a way to estimate quasar host dark matter halo masses, quantifying uncertainties due to cosmological and IGM parameters, and redshift errors. With this method, we examine data for ~3000 quasars from the Sloan Digital Sky Survey (SDSS) Data Release 3, assuming that the effect of ionizing radiation from quasars (the so-called transverse proximity effect) is unimportant (no evidence for it is seen in the data.) We find that the best fit host halo mass for SDSS quasars with mean redshift z=3 and absolute G band magnitude -27.5 is log10(M/M_sun) = 12.48^{+0.53}_{-0.89}. We also use the Lyman-Break Galaxy (LBG) and Lyman alpha forest data of Adelberger et al in a similar fashion to constrain the halo mass of LBGs to be log10(M/M_sun) = 11.13^{+0.39}_{-0.55}, a factor of ~20 lower than the bright quasars. In addition, we study the redshift distortions of the Lyman alpha forest around quasars, using the simulations. We use the quadrupole to monopole ratio of the quasar-Lyman alpha forest correlation function as a measure of the squashing effect. We find that this does not have a measurable dependence on halo mass, but may be useful for constraining cosmic geometry.
Here in this work we propose a modified gravity with the action of $f(R) = \sqrt{R^2 - R_0^2}$ instead of Einstein-Hilbert action to describe the late time acceleration of the universe. We obtain the equation of the modified gravity both in the metric and Palatini formalisms. An asymptotic solution of gravity equations corresponding to a constant Ricci scalar causes a late time acceleration of the universe. We do a conformal transformation in the action of the modified gravity and obtain the equivalent minimally coupled scalar-tensor gravity. The equivalent Brans-Dicke gravity of this model is also studied. To examine this model with the observation, the perihelion Precession of the Mercury is compared with our prediction and we put an upper constraint of $R_0<H_0^2$. This range for $R_0$ is also in agreement with the cosmological acceleration at the present time. Finally we show that this action has instability for the small perturbations of the metric in vacuum solution in which adding a quadratic term of Ricci scalar can stabilize it.
The process of reheating the universe after hybrid inflation is extremely violent. It proceeds through the nucleation and subsequent collision of large concentrations of energy density in bubble-like structures, which generate a significant fraction of energy in the form of gravitational waves. We study the power spectrum of the stochastic background of gravitational waves produced at reheating after hybrid inflation. We find that the amplitude could be significant for high-scale models, although the typical frequencies are well beyond what could be reached by planned gravitational wave observatories like LIGO, LISA or BBO. On the other hand, low-scale models could still produce a detectable stochastic background at frequencies accesible to those detectors. The discovery of such a background would open a new window into the very early universe.
An outstanding issue in braneworld theory concerns the setting up of proper boundary conditions for the brane-bulk system. Boundary conditions (BC's) employing regulatory branes or demanding that the bulk metric be nonsingular have yet to be implemented in full generality. In this paper, we take a different route and specify boundary conditions directly on the brane thereby arriving at a local and closed system of equations (on the brane). We consider a one-parameter family of boundary conditions involving the anisotropic stress of the projection of the bulk Weyl tensor on the brane and derive an exact system of equations describing scalar cosmological perturbations on a generic braneworld with induced gravity. Depending upon our choice of boundary conditions, perturbations on the brane either grow moderately (region of stability) or rapidly (instability). In the instability region, the evolution of perturbations usually depends upon the scale: small scale perturbations grow much more rapidly than those on larger scales. This instability is caused by a peculiar gravitational interaction between dark radiation and matter on the brane. Generalizing the boundary conditions introduced by Koyama and Maartens, we find for the Dvali-Gabadadze-Porrati (DGP) model an instability, which leads to a dramatic scale-dependence of the evolution of density perturbations in matter and dark radiation. A different set of BC's, however, leads to a more moderate and scale-independent growth of perturbations. For the mimicry braneworld, which expands like LCDM, this class of BC's can lead to an earlier epoch of structure formation.
Path length changes through the atmosphere cause significant errors for astronomical radio interferometry at high frequencies (e.g. 100 GHz). Path length differences typically give rise to a differential excess path of 1mm for antennas separated by 1km, and have fluctuation time scales of greater than 10 seconds. To measure these fluctuations, we are building a four-channel radiometer centred on the 22 GHz water line. By sensing the water vapour emission, the excess path can be deduced and corrected. Multiple channels give us robustness against various systematic errors, but gain stability of the radiometer of 1 pair in 10^4 is still required.
This article provides a concise review of the problem of neutrino radiation from dense matter. The subjects addressed include quantum kinetic equations for neutrino transport, collision integrals describing neutrino radiation through charged and neutral current interactions, radiation rates from pair-correlated baryonic and color superconducting quark matter.
Since its discovery, Malin 1 has been considered the prototype and most extreme example of the class of giant low surface brightness disk galaxies. Examination of an archival Hubble Space Telescope I-band image reveals that Malin 1 contains a normal stellar disk that was not previously recognized, having a central I-band surface brightness of mu_0 = 20.1 mag arcsec^-2 and a scale length of 4.8 kpc. Out to a radius of ~10 kpc, the structure of Malin 1 is that of a typical SB0/a galaxy. The remarkably extended, faint outer structure detected out to r~100 kpc appears to be a photometrically distinct component and not a simple extension of the inner disk. In terms of its disk scale length and central surface brightness, Malin~1 was originally found to be a very remote outlier relative to all other known disk galaxies. The presence of a disk of normal size and surface brightness in Malin 1 suggests that such extreme outliers in disk properties probably do not exist, but underscores the importance of the extended outer disk regions for a full understanding of the structure and formation of spiral galaxies.
It has recently been suggested that observed galaxy rotation curves can be accounted for by general relativity without recourse to dark-matter halos. A number of objections have been raised, which have been addressed by the authors. Here, the calculation of tangential velocity is questioned.
The Atacama Cosmology Telescope is a 6-meter telescope designed to map the Cosmic Microwave Background simultaneously at 145 GHz, 215 GHz, and 280 GHz with arcminute resolution. Each frequency will have a 32 by 32 element focal plane array of TES bolometers. This paper describes the design of the telescope and the cold reimaging optics, which is optimized for millimeter-wave observations with these sensitive detectors.
We present Global VLBI and HSA images of the gravitational lens B2016+112 at 18, 6 and 3.6 cm. Previous VLBI observations showed that images A and B (which are clearly lensed images of a single background source) and the elongated region C are each divided into components. Our new high-resolution maps reveal more components in images A and B, clearly demonstrating their expected opposite parities. According to the scenario of Koopmans et al. (2002), the arc-like region C consists of two merging, partial images (``C1-C2'') of just a small region of the same background source, seen with high lens magnification. We have determined the spectra and relative positions of the components within all four images in order to test this scenario. We find that the outer north-west components in images A and B do indeed have radio spectra similar to the components seen in C1 and C2.
Protostellar outflows crisscross the regions of star cluster formation, stirring turbulence and altering the evolution of the forming cluster. We model the stirring of turbulent motions by protostellar outflows, building on an observation that the scaling law of supersonic turbulence implies a momentum cascade analogous to the energy cascade in Kolmogorov turbulence. We then generalize this model to account for a diversity of outflow strengths, and for outflow collimation, both of which enhance turbulence. For a single value of its coupling coefficient the model is consistent with turbulence simulations by Li & Nakamura and, plausibly, with observations of the NGC 1333 cluster-forming region. Outflow-driven turbulence is strong enough to stall collapse in cluster-forming regions for several crossing times, relieving the mismatch between star formation and turbulent decay rates. The predicted line-width-size scaling implies radial density indices between -1 and -2 for regions supported by outflow-driven turbulence, with a tendency for steeper profiles in regions that are more massive or have higher column densities.
We present a spectral variability analysis of the X-ray emission of the
Narrow Line Seyfert 1 galaxy Ark 564 using the data from a
~100 ks XMM-Newton observation. Taking advantage of the high sensitivity of
this long observation and the simple spectral shape of Ark 564, we determine
accurately the spectral variability patterns in the source.
We use standard cross-correlation methods to investigate the correlations
between the soft and hard energy band light curves. We also generated 200
energy spectra from data stretches of 500 s duration each and fitted each one
of them with a power law plus a bremsstrahlung component (for the soft excess)
and we investigated the correlations between the various best fit model
parameter values. The ``power law plus bremsstrahlung'' model describes the
spectrum well at all times. The iron line and the absorption features, which
are found in the time-averaged spectrum of the source are too weak to effect
the results of the time resolved spectral fits. We find that the power law and
the soft excess flux are variable, on all measured time scales. The power law
slope is also variable, and leads the flux variations of both the power law and
the bremsstrahlung components. Our results can be explained in the framework of
time-dependent Comptonization models. They are consistent with a picture where
instabilities propagate through an extended X-ray source, affecting first the
soft and then the hard photons producing regions. The soft excess could
correspond to ionized disc reflection emission, in which case it responds fast
to the primary continuum variations. The time scales are such that light travel
times might additionally influence the observed variability structure.
(Abridged) In these lectures aimed for non-specialists, I review progress in understanding how galaxies form and evolve. Both the star formation history and assembly of stellar mass can be empirically traced from redshifts z~6 to the present, but how the various distant populations inter-relate and how stellar assembly is regulated by feedback and environmental processes remains unclear. I also discuss how these studies are being extended to locate and characterize the earlier sources beyond z~6. Did early star-forming galaxies contribute significantly to the reionization process and over what period did this occur? Neither theory nor observations are well-developed in this frontier topic but the first results presented here provide important guidance on how we will use more powerful future facilities.
The photospheric emission of a white dwarf (WD) is not expected to be detectable in hard X-rays or the mid-IR. Hard X-ray (~1 keV) emission associated with a WD is usually attributed to a binary companion; however, emission at 1 keV has been detected from three WDs without companions: KPD 0005+5106, PG 1159, and WD 2226-210. The origin of their hard X-ray emission is unknown, although it has been suggested that WD 2226-210 has a late-type companion whose coronal activity is responsible for the hard X-rays. Recent Spitzer observations of WD 2226-210 revealed mid-IR excess emission indicative of the existence of a dust disk. It now becomes much less clear whether WD 2226-210's hard X-ray emission originates from the corona of a late-type companion or from the accretion of the disk material. High-quality X-ray observations and mid-IR observations of KPD 0005+5106 and PG 1159 are needed to help us understand the origin of their hard X-ray emission.
Evidence for triggered star formation is difficult to establish because energy feedback from massive stars tend to erase the interstellar conditions that led to the star formation. Young stellar objects (YSOs) mark sites of {\it current} star formation whose ambient conditions have not been significantly altered. Spitzer observations of the Large Magellanic Cloud (LMC) effectively reveal massive YSOs. The inventory of massive YSOs, in conjunction with surveys of interstellar medium, allows us to examine the conditions for star formation: spontaneous or triggered. We examine the relationship between star formation and gravitational instability on a global scale, and we present evidence of triggered star formation on local scales in the LMC.
We have calculated the cosmic ray (CR) acceleration at young remnants from Type Ia supernovae expanding into a uniform interstellar medium (ISM). Adopting quasi-parallel magnetic fields, gasdynamic equations and the diffusion convection equation for the particle distribution function are solved in a comoving spherical grid which expands with the shock. Bohm-type diffusion due to self-excited Alfven waves, drift and dissipation of these waves in the precursor and thermal leakage injection were included. With magnetic fields amplified by the CR streaming instability, the particle energy can reach up to 10^{16}Z eV at young supernova remnants (SNRs) of several thousand years old. The fraction of the explosion energy transferred to the CR component asymptotes to 40-50 % by that time. For a typical SNR in a warm ISM, the accelerated CR energy spectrum should exhibit a concave curvature with the power-law slope flattening from 2 to 1.6 at E>0.1 TeV.
A correlation between the metallicity, [M/H], and rest-frame MgII equivalent width, EW, is found from 49 DLAs and strong sub-DLAs drawn from the literature over the redshift range 0.2<z_abs<2.6. The correlation is significant at 4.2 sigma and improves to 4.7 sigma when the mild evolution of [M/H] with redshift is taken into account. Even when including only the 26 DLAs (i.e. excluding sub-DLAs) which have Zn metallicities and EW>0.7A, the correlation remains at >3 sigma significance. Since the MgII2796 transition is predominantly saturated in DLAs (which always have EW greater than 0.3A), EW is far more sensitive to the kinematic spread of the metal velocity components across the absorption profile than it is to [M/H]. Thus, the observed [M/H]--EW correlation points to a strong link between the absorber metallicity and the mechanism for producing and dispersing the velocity components. We also note that approximately half of the 13 known molecular hydrogen absorbers have very high EW and very broad velocity structures which show characteristics usually associated with outflows. Follow-up ultraviolet- and blue-sensitive high-resolution spectra of high-EW systems, initially identified in low-resolution spectra, may therefore yield a large number of new H_2 discoveries.
With numerical experiments we explore the feasibility of using high frequency waves for probing the magnetic fields in the photosphere and the chromosphere of the Sun. We track a plane-parallel, monochromatic wave that propagates through a non-stationary, realistic atmosphere, from the convection-zone through the photosphere into the magnetically dominated chromosphere, where it gets refracted and reflected. We compare the wave travel time between two fixed geometrical height levels in the atmosphere (representing the formation height of two spectral lines) with the topography of the surface of equal magnetic and thermal energy density (the magnetic canopy or beta=1 contour) and find good correspondence between the two. We conclude that high frequency waves indeed bear information on the topography of the `magnetic canopy'.
The magnetorotational instability (MRI) plays a key role in the formation of stars and black holes, by enabling outward angular momentum transport in accretion disks. The use of combined axial and azimuthal magnetic fields allows the investigation of this effect in liquid metal flows at moderate Reynolds and Hartmann numbers. A variety of experimental results is presented showing evidence for the occurrence of the MRI in a Taylor-Couette flow using the liquid metal alloy GaInSn.
Several pairs of observable properties of Gamma Ray Bursts (GRBs) are known to be correlated. Many such correlations are straightforward predictions of the 'cannonball' model of GRBs. We extend our previous discussions of the subject to a wealth of new data, and to correlations between 'lag-time', 'variability' and 'minimum rise-time', with other observables. Schaefer's recent systematic analysis of the observations of many GRBs of known red-shift gives us a good and updated data-basis for our study.
Aims. Continuing the systematic determination of the electron temperature of H II regions using the Balmer and/or Paschen discontinuities by Guseva et al. (2006) we focus here on 3.6m ESO telescope observations of a large new sample of 69 H II regions in 45 blue compact dwarf (BCD) galaxies. This data set spans a wide range in metallicity (Zsun/60<Z<Zsun/3) and, combined with the sample of 47 H II regions from Guseva et al. (2006), yields the largest spectroscopic data set ever used to derive the electron temperature in the H+ zone. Methods. In the same way as in Guseva et al. (2006) we have used a Monte Carlo technique to vary free parameters and to calculate a series of model spectral energy distributions (SEDs) for each H II region. The electron temperature in the H+ zones was derived from the best fitting synthetic and observed SEDs in the wavelength range ~3200-5100A, which includes the Balmer jump. Results. On the base of the present large spectroscopic sample we find that in hot (Te(H+)>11000 K) H II regions the temperature of the O2+ zone, determined from doubly ionised oxygen forbidden lines, does not differ statistically from the temperature of the H+ zone. Thus, we confirm and strengthen the finding by Guseva et al. (2006). We emphasize that due to a number of modelling assumptions and the observational uncertainties for individual objects, only a large, homogeneous sample, as the one used here, can enable a conclusive study of the relation between Te(H+) and Te(O III).
Recent observations have revealed the existence of enormously energetic \~10^61 erg AGN outbursts in three relatively distant galaxy clusters. These outbursts have produced cavities in the intra-cluster medium, apparently supported by pressure from relativistic particles. Here we argue that these particles are very likely protons and nuclei, rather than electrons, and that the gamma-ray emission from these objects, arising from the interactions of these hadrons in the intra-cluster medium, may be detectable with instruments such as GLAST and H.E.S.S.
We present high resolution VLT UVES and low resolution FORS optical spectroscopy of supernova 2006aj and its host galaxy, associated with the nearby (z = 0.03342) gamma-ray burst GRB 060218. This host galaxy is a unique case, as it is one of the few nearby GRB host galaxies known, and it is only the second time high resolution spectra have been taken of a nearby GRB host galaxy (after GRB 980425). The resolution, wavelength range and S/N of the UVES spectrum combined with low resolution FORS spectra allow a detailed analysis of the circumburst and host galaxy environments. We analyse the emission and absorption lines in the spectrum, combining the high resolution UVES spectrum with low resolution FORS spectra and find the metallicity and chemical abundances in the host. We probe the geometry of the host by studying the emission line profiles. Our spectral analysis shows that the star forming region in the host is metal poor with 12 + log(O/H) = 7.54 (+0.17, -0.10) (~0.07 Z_sun), placing it among the most metal deficient subset of emission-line galaxies. It is also the lowest metallicity found so far for a GRB host from an emission-line analysis. Given the stellar mass of the galaxy of ~10^7 M_sun and the SFR (H alpha) = 0.065 +/- 0.005 M_sun/yr, the high specific star formation rate indicates an age for the galaxy of less than ~200 Myr. The brightest emission lines are clearly asymmetric and are well fit by two Gaussian components separated by ~22$ km/s. We detect two discrete Na I and Ca II absorption components at the same redshifts as the emission components. We tentatively interpret the two components as arising from two different starforming regions in the host, but high resolution imaging is necessary to confirm this.
An analysis is presented of a numerical investigation of the dynamics and geometry of accretion discs in binary systems with mass ratios q < 0.1, applicable to ultra-compact X-ray binaries, AM CVn stars and very short period cataclysmic variables. The steady-state geometry of the disc in the binary reference frame is found to be quite different from that expected at higher mass ratios. For q ~ 0.1, the disc takes on the usual elliptical shape, with the major axis aligned perpendicular to the line of centres of the two stars. However, at smaller mass ratios the elliptical gaseous orbits in the outer regions of the disc are rotated in the binary plane. The angle of rotation increases with gas temperature, but is found to vary inversely with q. At q = 0.01, the major axis of these orbits is aligned almost parallel to the line of centres of the two stars. These effects may be responsible for the similar disc structure inferred from Doppler tomography of the AM CVn star GP Com (Morales-Rueda et al. 2003), which has q = 0.02. The steady-state geometry at low mass ratios is not predicted by an inviscid, restricted three-body model of gaseous orbits; it is related to the effects of tidal-viscous truncation of the disc near the Roche lobe boundary. Since the disc geometry can be inferred observationally for some systems, it is proposed that this may offer a useful diagnostic for the determination of mass ratios in ultra-compact binaries.
Water vortices are known to develop polygon structures inside their cores. The apexes of the polygonal manifestations are the result of satellite vortices attached to the parent vortex. Exploiting the analogy between the shallow water hydraulics and the two-dimensional compressible gas flows we arrive to the following line of reasoning concerning the spiral galactic structure. The backward free surface fore ripples of the advancing pressure disturbance in the hydraulic system should appear as high-density spirals in the gaseous galactic disk. Since the number of galactic arms is equal to the number of satellite eddies in the parent vortex, spiral galaxies with say two arms will possess two nuclei. The last appears to be in complete agreement with the latest observations regarding M 31 and Mrk 315 galaxies. If the present hypothesis is accurate then a closer look at the central regions of multi-tentacle spiral galaxies should also reveal that these have multiple nuclei.
We have used the ionisation equilibrium equation to derive the electron
density in interstellar clouds in the direction to 13 stars. A linear relation
was found, that allows the determination of the electron density from the Mg I
and Mg II column densities in interstellar medium.
The comparison of normalised equivalent width of 12 DIBs with the electron
density shows that the DIBs equivalent width do not change with varying
electron density. Therefore the DIBs carriers (1) can be observed only in one
ionisation stage, or (2) the DIBs are arising in cloud regions (cores or cloud
coronas) for which we can not determine the electron density.
We have used the VLBI High Sensitivity Array (VLBA with VLA, Green Bank Telescope, and Arecibo) to search for young radio supernovae in three nearby Wolf Rayet dwarf galaxies containing Super Star Clusters (SSCs) and signs of extreme star formation in the last few million years. No milliarcsecond radio sources were detected in II Zw 40, He 2-10, or NGC 5253, implying that these galaxies contain few radio supernovae, despite the fact that they have at least some star formation going back to 10 million years ago. The upper limits of the source powers range from 6 x 10^17 W/Hz to ~2 x 10^18 W/Hz at 5 GHz, roughly 0.6 to 2.2 times the power of the galactic supernova remnant Cassiopeia A. Comparison with the radio supernova population in Arp 299 implies that the current supernova rates in the three dwarf galaxies are below 10^{-2}/yr, consistent with standard star formation models that predict supernova rates of 10^{-3}/yr or less in our targets. In He 2-10, the VLBI non-detection of a compact VLA source with a significant nonthermal component indicates that this source may be dominated by one or more supernova remnants with ages of a few hundred years or more, which are comparable to Cas~A in power, and size.
We report on the results of a study to obtain limits on the absorbing columns to wards an initial sample of 10 long Gamma-Ray Bursts observed with BeppoSAX, using a new approach to SED fitting to nIR, optical and X-ray afterglow data, in count space and including the effects of metallicity. When testing MW, LMC and SMC extinction laws we find that SMC-like extinction provides the best fit in most cases. A MW-like ext inction curve is not preferred for any of these sources, largely since the 2175A bump, in principle detectable in all these afterglows, is not present in the data. We rule out an SMC-like gas-to-dust ratio or lower value for 4 of the hosts analysed here (assuming SMC metallicity and extinction law) whilst the remainder of the sample have too large an error to discriminate. We provide an accurate estimate of the line-of-sight extinction, improving upon the uncertainties for the majority of the extinction measurements made in previous studies of this sample.
By combining the 0.12 square degree F814W Hubble Space Telescope (HST) and Spitzer MIPS 24 micron imaging in the First Look Survey (FLS), we investigate the properties of interacting and merging Mid-Infrared bright and faint sources at 0.2< z <1.3. We find a marginally significant increase in the pair fraction for MIPS 24 micron detected, optically selected close pairs, pair fraction=0.25+/-0.10 at z~1, in contrast to 0.11+/-0.08 at z~0.4, while galaxies below our 24 micron MIPS detection limit show a pair fraction consistent with zero at all redshifts. Additionally, 24 micron detected galaxies with fluxes >0.1mJy are on average five times more likely to be in a close galaxy pair between 0.2< z <1.3 than galaxies below this flux limit. Using the 24 micron flux to derive the total Far-IR luminosity we find that paired galaxies (early stage mergers) are responsible for 27% +/-9% of the IR luminosity density resulting from star formation at z~1 while morphologically classified (late stage) mergers make up 34%+/-11%. This implies that 61%+/-14% of the infrared luminosity density and in turn ~40% of the star formation rate density at z~1 can be attributed to galaxies at some stage of a major merger or interaction. We argue that, close pairs/mergers in a LIRG/ULIRG phase become increasingly important contributers to the IR luminosity and star formation rate density of the Universe at z>0.7.
We present constraints on the dark energy equation-of-state parameter, w=P/(rho c^2), using 60 Type Ia supernovae (SNe Ia) from the ESSENCE supernova survey. We derive a set of constraints on the nature of the dark energy assuming a flat Universe. By including constraints on (Omega_M, w) from baryon acoustic oscillations, we obtain a value for a static equation-of-state parameter w=-1.05^{+0.13}_{-0.12} (stat; 1 sigma) +- 0.11 (sys) and Omega_M=0.274^{+0.033}_{-0.020} (stat; 1 sigma) with a best-fit chi^2/DoF of 0.96. These results are consistent with those reported by the SuperNova Legacy Survey in a similar program measuring supernova distances and redshifts. We evaluate sources of systematic error that afflict supernova observations and present Monte Carlo simulations that explore these effects. Currently, the largest systematic currently with the potential to affect our measurements is the treatment of extinction due to dust in the supernova host galaxies. Combining our set of ESSENCE SNe Ia with the SuperNova Legacy Survey SNe Ia, we obtain a joint constraint of w=-1.07^{+0.09}_{-0.09} (stat; 1 sigma) +- 0.12 (sys), Omega_M=0.267^{+0.028}_{-0.018} (stat; 1 sigma) with a best-fit chi^2/DoF of 0.91. The current SN Ia data are fully consistent with a cosmological constant.
We show that the Lyman-alpha (Ly-alpha) optical depth statistics in the proximity regions of quasar spectra depend sensitively on the mass of the dark matter halos hosting the quasars. This is owing to both the overdensity around the quasars and the associated infall of gas toward them. For a fiducial quasar host halo mass of (3.0 +/- 1.6) h^-1 x 10^12 M_sun, as inferred by Croom et al. from clustering in the 2dF QSO Redshift Survey, we show that estimates of the ionizing background (Gamma^bkg) from proximity effect measurements that neglect these effects could be biased high by a factor of ~2.5 at z=3. The clustering of galaxies and other active galactic nuclei around the proximity effect quasars enhances the local background, but is not expected to skew measurements by more than a few percent. Assuming the measurements of Gamma^bkg based on the mean flux decrement in the Ly-alpha forest to be free of bias, we demonstrate how the proximity effect analysis can be inverted to measure the mass of the dark matter halos hosting quasars. In ideal conditions, such a measurement could be made with a precision comparable to the best clustering constraints to date from a modest sample of only about 100 spectra. Existing line-of-sight proximity effect measurements of Gamma^bkg (which have assumed that the quasars lie in random locations of the Universe) are a factor of 2-3 higher than the independent flux decrement measurements at z~3. This work thus provides tantalizing evidence for a picture in which proximity effect and flux decrement measurements of Gamma^bkg, as well as clustering measurements of quasar host halo masses, are all consistent with each other when the proximity regions of quasars are realistically modeled as being part of overdense regions and opens the way to proximity effect measurements of dark matter halo masses.
We describe the implementation and optimization of the ESSENCE supernova survey, which we have undertaken to measure the equation of state parameter of the dark energy. We present a method for optimizing the survey exposure times and cadence to maximize our sensitivity to the dark energy equation of state parameter w=P/rho c^2 for a given fixed amount of telescope time. For our survey on the CTIO 4m telescope, measuring the luminosity distances and redshifts for supernovae at modest redshifts (z~0.5 +- 0.2) is optimal for determining w. We describe the data analysis pipeline based on using reliable and robust image subtraction to find supernovae automatically and in near real-time. Since making cosmological inferences with supernovae relies crucially on accurate measurement of their brightnesses, we describe our efforts to establish a thorough calibration of the CTIO 4m natural photometric system. In its first four years, ESSENCE has discovered and spectroscopically confirmed 102 type Ia SNe, at redshifts from 0.10 to 0.78, identified through an impartial, effective methodology for spectroscopic classification and redshift determination. We present the resulting light curves for the all type Ia supernovae found by ESSENCE and used in our measurement of w, presented in Wood-Vasey et al, 2007.
We study the motion of stars in a star cluster which revolves in a circular orbit about its parent galaxy. The star cluster is modelled as an ellipsoid of uniform spatial density. We exhibit two 2-parameter families of self-consistent equilibrium models in which the velocity at each point is confined to a line in velocity space. We exhibit the link between this problem and that of a uniform rotating ellipsoidal galaxy. With minimal adaptation, Freeman's bar models yield a third family.
We have selected 14 J-dropout Lyman Break Galaxy (LBG) candidates with J110 - H160 > 2.5 from the NICMOS Parallel Imaging Survey. This survey consists of 135 square arcminutes of imaging in 228 independent sight lines, reaching average 5 sigma sensitivities of J110 = 25.8 and H160 = 25.6 (AB). Distinguishing these candidates from dust reddened star forming galaxies at z ~ 2-3 is difficult, and will require longer wavelength observations. We consider the likelihood that any J-dropout LBGs exist in this survey, and find that if L*(z=9.5) is significantly brighter than L*(z=6) (a factor of four), then a few J-dropout LBGs are likely. A similar increase in luminosity has been suggested by Eyles et al. and Yan et al., but the magnitude of this increase is uncertain.
The Swift X-ray Telescope (XRT) has discovered that flares are quite common in early X-ray afterglows of Gamma-Ray Bursts (GRBs), being observed in roughly 50% of afterglows with prompt followup observations. The flares range in fluence from a few percent to ~ 100% of the fluence of the prompt emission (the GRB). Repetitive flares are seen, with more than 4 successive flares detected by the XRT in some afterglows. The rise and fall times of the flares are typically considerably smaller than the time since the burst. These characteristics suggest that the flares are related to the prompt emission mechanism, but at lower photon energies. We conclude that the most likely cause of these flares is late-time activity of the GRB central engine.
We summarize some of the new results from contributions made to the Galactic Centre Workshop that took place in Bad Honnef, Germany, on April 18-22, 2006.
Close-in giant planets are thought to have formed in the cold outer regions of planetary systems and migrated inward, passing through the orbital parameter space occupied by the terrestrial planets in our own Solar System. We present dynamical simulations of the effects of a migrating giant planet on a disk of protoplanetary material and the subsequent evolution of the planetary system. We numerically investigate the dynamics of post-migration planetary systems over 200 million years using models with a single migrating giant planet, one migrating and one non-migrating giant planet, and excluding the effects of a gas disk. Material that is shepherded in front of the migrating giant planet by moving mean motion resonances accretes into "hot Earths", but survival of these bodies is strongly dependent on dynamical damping. Furthermore, a significant amount of material scattered outward by the giant planet survives in highly excited orbits; the orbits of these scattered bodies are then damped by gas drag and dynamical friction over the remaining accretion time. In all simulations Earth-mass planets accrete on approximately 100 Myr timescales, often with orbits in the Habitable Zone. These planets range in mass and water content, with both quantities increasing with the presence of a gas disk and decreasing with the presence of an outer giant planet. We use scaling arguments and previous results to derive a simple recipe that constrains which giant planet systems are able to form and harbor Earth-like planets in the Habitable Zone, demonstrating that roughly one third of the known planetary systems are potentially habitable.
Direct identification of the progenitors of supernovae (SNe) is rare because of the required spatial resolution and depth of the archival data prior to the SN explosions. Here we report the identification of the progenitors of two nearby SNe in the Virgo cluster: SN 2006my in NGC 4651 and SN 2006ov in M61. We obtained high-quality ground-based images of SN 2006my with the Canada-France-Hawaii Telescope, and are able to locate the site of the SN on pre-SN {\it Hubble Space Telescope} ({\it HST}) Wide Field Planetary Camera 2 (WFPC2) images to a high precision (1$\sigma$ uncertainty of $\pm0\farcs$05). We pinpoint the site of SN 2006ov to within 0$\farcs$02 from {\it HST} Advanced Camera for Surveys (ACS) images of the SN. We detected a red supergiant progenitor for each SN within the error circles, with an inferred zero-age main-sequence mass of 7--15 $M_\odot$ and 12--20 $M_\odot$ for the progenitor of SNe 2006my and 2006ov, respectively. The mass estimates for the progenitors of both SNe confirm an early trend that the most common Type II-plateau SNe originate from low-mass supergiants (8--20 $M_\odot$).
The magnetic field within a few hundred parsecs of the center of the Galaxy is an essential component of any description of that region. The field has several pronounced observational manifestations: 1) morphological structures such as nonthermal radio filaments (NTFs) -- magnetic flux tubes illuminated by synchrotron emission from relativistic electrons -- and a remarkable, large-scale, helically wound structure, 2) relatively strong polarization of thermal dust emission from molecular clouds, presumably resulting from magnetic alignment of the rotating dust grains, and 3) synchrotron emission from cosmic rays. Because most of the NTFs are roughly perpendicular to the Galactic plane, the implied large-scale geometry of the magnetic field is dipolar. Estimates of the mean field strength vary from tens of microgauss to ~ a milligauss. The merits and weaknesses of the various estimations are discussed here. If the field strength is comparable to a milligauss, then the magnetic field is able to exert a strong influence on the dynamics of molecular clouds, on the collimation of a Galactic wind, and on the lifetimes and bulk motions of relativistic particles. Related to the question of field strength is the question of whether the field is pervasive throughout the central zone of the Galaxy, or whether its manifestations are predominantly localized phenomena. Current evidence favors the pervasive model.
In this contribution initial results from colour-magnitude diagrams for five dEs in the M81 group are presented. The colour-magnitude diagrams, derived from HST/ACS images, reach well below the red giant branch tip and allow evaluation of distances and mean metallicities. Further, the intermediate-age upper-AGB stars seen in the diagrams allow estimates of the epochs of the last significant episode of star formation in the dEs. These epochs, and the relative numbers of upper-AGB to red giant branch stars, vary significantly from dE to dE. Preliminary inferences from similar HST/ACS data for five early-type dwarfs in the Sculptor group are also discussed.
We briefly summarize and update a class of inflationary models from the early eighties based on a quartic (Coleman-Weinberg) potential for a gauge singlet scalar (inflaton) field. For vacuum energy scales comparable to the grand unification scale, the scalar spectral index n_s=0.94-0.97, in very good agreement with the WMAP three year results. The tensor to scalar ratio r<~0.14 while alpha=dn_s/d ln k=~-10^-3. For vacuum energy scales >~10^16 GeV, the inflationary scenario switches from `new' to `large-field' (V\propto\phi^2) inflation. An SO(10) version naturally explains the observed baryon asymmetry via non-thermal leptogenesis.
We present first results of near infrared J and H+K ESO-SINFONI integral field spectroscopy of the composite starburst/Seyfert 1.8 galaxy Mrk 609. The data were taken during the science verification period of SINFONI. We aim to investigate the morphology and excitation conditions within the central 2 kpc. Additional Nobeyama 45 m CO(1-0) data are presented, which we used to estimate the molecular gas mass. The source was selected from a sample of adaptive optics suitable, SDSS/ROSAT based, X-ray bright AGN with redshifts of 0.03 < z < 1. This sample allows for a detailed study of the NIR properties of the nuclear and host environments with high spectral and spatial resolution. Our NIR data reveal a complex emission-line morphology, possibly associated with a nuclear bar seen in the reconstructed continuum images. The detections of [SiVI] and a broad Pa alpha component are clear indicators for the presence of an accreting super-massive black hole at the center of Mrk 609. In agreement with previous observations we find that the circum-nuclear emission is not significantly extincted. The analysis of the high angular resolution rotational-vibrational molecular hydrogen and forbidden [FeII] emission reveals a LINER character of the nucleus. The large H_2 gas mass deduced from the CO(1-0) observation provides the fuel needed to feed the starburst and Seyfert activity in Mrk 609. High angular resolution imaging spectroscopy provides an ideal tool to resolve the nuclear and starburst contribution in active galaxies. We show that Mrk 609 exhibits LINER features, that appear to be hidden in larger aperture visible/NIR spectra.
Magnetic fields are an important but largely unknown ingredient of planetary nebulae. They have been detected in oxygen-rich AGB and post-AGB stars, and may play a role in the shaping of their nebulae. Here we present SCUBA sub-millimeter polarimetric observations of four bipolar planetary nebulae and post-AGB stars, including two oxygen-rich and two carbon-rich nebulae, to determine the geometry of the magnetic field by dust alignment. Three of the four sources (NGC 7027, NGC 6537 and NGC 6302) present a well-defined toroidal magnetic field oriented along their equatorial torus or disk. NGC 6302 may also show field lines along the bipolar outflow. CRL 2688 shows a complex field structure, where part of the field aligns with the torus, whilst an other part approximately aligns with the polar outflow. It also presents marked asymmetries in its magnetic structure. NGC 7027 shows evidence for a disorganized field in the south-west corner, where the SCUBA shows an indication for an outflow. The findings show a clear correlation between field orientation and nebular structure.
We present the activity and kinematics of a representative volume-limited (20 pc) sample of 152 late-M and L dwarfs (M7--L8) photometrically selected from the Two Micron All-Sky Survey (2MASS). Using new proper motion measurements and spectrophotometric distance estimates, we calculate tangential velocities. The sample has a mean tangential velocity of <V_tan> = 31.5 km/s, a velocity dispersion of sigma_tan = 20.7 km/s, and a maximum tangential velocity of V_tan = 138.8 km/s. These kinematic results are in excellent agreement with previous studies of ultracool dwarfs in the local solar neighborhood. H_alpha emission, an indicator of chromospheric activity, was detected in 63 of 81 late-M dwarfs and 16 of 69 L dwarfs examined. We find a lack of correlation between activity strength, measured by log(F_H_alpha/F_bol), and V_tan, though velocity distributions suggest that the active dwarfs in our sample are slightly younger than the inactive dwarfs. Consistent with previous studies of activity in ultracool dwarfs, we find that the fraction of H$\alpha$ emitting objects per spectral type peaks at spectral type M7 and declines through mid-L dwarfs. Activity strength is similarly correlated with spectral type for spectral types later than M7. Eleven dwarfs out of 150 show evidence of variability, ranging from small fluctuations to large flare events. We estimate a flare cycle of ~5% for late-M dwarfs and ~2% for L dwarfs. Observations of strong, variable activity on the L1 dwarf 2MASS J10224821+5825453 and an amazing flare event on the the M7 dwarf 2MASS J1028404$-$143843 are discussed.
Large scale dynamo-generated fields are a combination of interlocked poloidal and toroidal fields. Such fields possess magnetic helicity that needs to be regenerated and destroyed during each cycle. A number of numerical experiments now suggests that stars may do this by shedding magnetic helicity. In addition to plain bulk motions, a favorite mechanism involves magnetic helicity flux along lines of constant rotation. We also know that the sun does shed the required amount of magnetic helicity mostly in the form of coronal mass ejections. Solar-like stars without cycles do not face such strong constraints imposed by magnetic helicity evolution and may not display coronal activity to that same extent. I discuss the evidence leading to this line of argument. In particular, I discuss simulations showing the generation of strong mean toroidal fields provided the outer boundary condition is left open so as to allow magnetic helicity to escape. Control experiments with closed boundaries do not produce strong mean fields.
The outer surface layers of the sun show a clear deceleration at low latitudes. This is generally thought to be the result of a strong dominance of vertical turbulent motions associated with strong downdrafts. This strong negative radial shear should not only contribute to amplifying the toroidal field locally and to expelling magnetic helicity, but it may also be responsible for producing a strong prograde pattern speed in the supergranulation layer. Using simulations of rotating stratified convection in cartesian boxes located at low latitudes around the equator it is shown that in the surface layers patterns move in the prograde direction on top of a retrograde mean background flow. These patterns may also be associated with magnetic tracers and even sunspot proper motions that are known to be prograde relative to the much slower surface plasma.
We provide an overview of the Spitzer Legacy Program ``Formation and
Evolution of Planetary Systems" (FEPS) which was proposed in 2000, begun in
2001, and executed aboard the Spitzer Space Telescope between 2003 and 2006.
This program exploits the sensitivity of Spitzer to carry out mid-infrared
spectrophotometric observations of solar-type stars. With a sample of ~ 328
stars ranging in age from ~ 3 Myr to ~ 3 Gyr, we trace the evolution of
circumstellar gas and dust from primordial planet-building stages in young
circumstellar disks through to older collisionally generated debris disks. When
completed, our program will help define the time scales over which terrestrial
and gas giant planets are built, constrain the frequency of planetesimal
collisions as a function of time, and establish the diversity of mature
planetary architectures.
In addition to the observational program, we have coordinated a concomitant
theoretical effort aimed at understanding the dynamics of circumstellar dust
with and without the effects of embedded planets, dust spectral energy
distributions, and atomic and molecular gas line emission. Together with the
observations, these efforts will provide astronomical context for understanding
whether our Solar System - and its habitable planet - is a common or a rare
circumstance. Additional information about the FEPS project can be found on the
team website: feps.as.arizona.edu
We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.
We have modeled the rotational modulation of X-ray emission from T Tauri stars assuming that they have isothermal, magnetically confined coronae. By extrapolating surface magnetograms we find that T Tauri coronae are compact and clumpy, such that rotational modulation arises from X-ray emitting regions being eclipsed as the star rotates. Emitting regions are close to the stellar surface and inhomogeneously distributed about the star. However some regions of the stellar surface, which contain wind bearing open field lines, are dark in X-rays. From simulated X-ray light curves, obtained using stellar parameters from the Chandra Orion Ultradeep Project, we calculate X-ray periods and make comparisons with optically determined rotation periods. We find that X-ray periods are typically equal to, or are half of, the optical periods. Further, we find that X-ray periods are dependent upon the stellar inclination, but that the ratio of X-ray to optical period is independent of stellar mass and radius.
An extraordinary event took place recently in Ireland. A group of independent and professional researchers met to discuss an old heterodox topic with important consequences in astrophysics and, especially, in cosmology: possible causes of the redshifts in the spectra of astrophysical objects other than a Doppler or expanding universe mechanism. Many decades of work have been devoted to this kind of research, most of it forgotten by the greater part of the astrophysical community nowadays. But the question is still open, the debate is still alive, as was shown by the participants in the present Workshop. There is no smoke without fire, and the existence of many facts and theories on alternative origins of redshifts may point to some new pathways in physics that deserve further attention. This was precisely the aim of this meeting. (...)
Asymptotic Giant Branch (AGB) stars are important players in the chemical evolution modelling of galaxies, because they are major producers of several chemical elements and excellent tracers of the structure and of the star formation activity of their parent galaxies. A few examples on the importance of AGB stars are presented in this review, together with a number of open problems affecting chemical evolution model predictions related to the element enrichment by AGB stars: the evolution of $^4$He and Na in globular clusters, the evolution of $^3$He and the carbon isotopes in the Galactic disk, and the evolution of N and O in different types of galaxies. The need of homogeneous and complete sets of yields is emphasized.
The levitation height of a dust particle layer within a RF discharge plasma sheath is known to be related to the DC bias, the background pressure, and the Debye length. In this paper, a new experimental technique for measurement of the Debye length is introduced. This technique is based on the relationship between an externally applied DC bias and the particle levitation height and shows that under appropriate conditions, the addition of an externally applied DC bias provides a mechanism for evaluation of the Debye length. When compared with existing techniques, this new method appears to be simpler to implement in some cases.
We compute the distribution of velocities of the particles ejected by the
impact of the projectile released from NASA Deep Impact spacecraft on the
nucleus of comet 9P/Tempel 1 on the successive 20 hours following the
collision. This is performed by the development and use of an ill-conditioned
inverse problem approach, whose main ingredients are a set of observations
taken by the Narrow Angle Camera (NAC) of OSIRIS onboard the Rosetta
spacecraft, and a set of simple models of the expansion of the dust ejecta
plume for different velocities. Terminal velocities are derived using a maximum
likelihood estimator.
We compare our results with published estimates of the expansion velocity of
the dust cloud. Our approach and models reproduce well the velocity
distribution of the ejected particles. We consider these successful comparisons
of the velocities as an evidence for the appropriateness of the approach. This
analysis provides a more thorough understanding of the properties of the Deep
Impact dust cloud.
Many models for ultra-high energy cosmic rays postulate exotic scenarios to explain the sources or the nature of these particles. A characteristic feature of these models is the prediction of a significant flux of photons at ultra-high energy. The Pierre Auger Observatory offers a great potential to search for such photons. We present shower observables with sensitivity to photons and the search strategy employed. An upper limit to photon primaries is derived from first Auger data. Prospects for constraining theoretical source models are discussed.
A survey of 49 HST WFPC2 pointings in M31 has resulted in a photometric catalog of 344 disk clusters ("open clusters"). We have analyzed the color-magnitude diagram, the luminosity function, the size distribution and the age distribution of the clusters, together with correlations between these characteristics and the environment of the clusters within M31's spiral structure.
Context: The very young sigma Orionis cluster (about 3 Ma) is a cornerstone for the understanding of the formation of stars and substellar objects down to planetary masses. However, its stellar population is far to be completely known. Aims: This study has the purpose of identyfing and characterising the most massive stars of sigma Orionis to complement current and future deep searches for brown dwarfs and planetary-mass objects in the cluster. Methods: I have cross-correlated the sources in the Tycho and 2MASS catalogues in a region of 30 arcmin radius with centre in the O-type star sigma Ori A. In the area, I have studied the membership in the Ori OB 1b Association of the brightest stars in the optical using astrometric, X-ray and infrared and optical photometric data from public catalogues and spectroscopic data from the literature. Results: A list of 26 young stars, four candidate young stars and 16 probable foreground stars has arised from the study. Seven young stars probably harbour discs (four are new). There is no mass-dependence of the disc frequency in the cluster. I have derived for the first time the mass spectrum in sigma Orionis from 1.1 to 24 Msol (alpha = +2.0+0.2-0.1; roughly Salpeter-like). I have also provided additional proofs on the existence of several spatially superimposed stellar populations in the direction of sigma Orionis. Finally, the cluster may be closer and older than previously considered.
The All Sky Automated Survey (ASAS) monitors bright stars (8 mag < V < 14 mag) south of declination +28 deg. The ASAS Catalogue of Variable Stars (ACVS) presently contains 50,099 objects; among them are 2212 objects classified as RR Lyrae pulsating variables. We use ASAS photometric V band data to search for multiperiodicity in those stars. We find that 73 of 1435 RRab stars and 49 of 756 RRc stars exhibit the Blazhko effect. We observe a deficiency of RRab Blazhko variables with main pulsation periods greater than 0.65 days. The Blazhko periods of RRc stars exhibit a strongly bimodal distribution. During our study we discovered the Blazhko effect with multiple periods in object ASAS 050747-3351.9 = SU Col. Blazhko periods of 89.3 d and 65.8 d and a candidate of 29.5 d were identified with periodogram peaks near the first three harmonics of the main pulsation. These observations may inspire new models of the Blazhko effect, which has eluded a consistent theory since its discovery about one hundred years ago. Long term lightcurve changes were found in 29 stars. We also found 19 Galactic double mode pulsators (RRd), of which 4 are new discoveries, raising the number of ASAS discoveries of such objects to 16, out of 27 known in the field of our Galaxy.
The field of the extended TeV source HESS J1804-216 was serendipitously observed with the Chandra ACIS detector. The data reveal several X-ray sources within the bright part of HESS J1804-216. The brightest of these objects, CXOU J180432.4-214009, which has been also detected with Swift and Suzaku, is consistent with being a point-like source, with the 0.3-7 keV flux of (1.7\pm0.2)\times10^{-13} ergs s^{-1} cm^{-2}. Its hard and strongly absorbed spectrum can be fitted by the absorbed power-law model with the best-fit photon index of 0.45 and hydrogen column density of 4\times10^{22} cm^{-2}, both with large uncertainties due to the strong correlation between these parameters. A search for pulsations resulted in a 106 s period candidate, which however has a low significance of 97.9%. We found no infrared-optical counterparts for this source. The second brightest source, CXOU J180441.9-214224, which has been detected with Suzaku, is either extended or multiple, with the flux of about 10^{-13} ergs cm^{-2} s^{-1}. We found a nearby M dwarf within the X-ray source extension, which could contribute a fraction of the observed X-ray flux. The remaining sources are very faint (<3\times 10^{-14} ergs cm^{-2} s^{-1}), and at least some of them are likely associated with nearby stars. Although one or both of the two brighter X-ray sources could be faint accreting binaries or remote pulsars with pulsar wind nebulae (hence possible TeV sources), their relation to HESS J1804-216 remains elusive. The possibility that HESS J1804-216 is powered by the relativistic wind from the young pulsar B1800-21, located at a distance of about 10 pc from the TeV source, still remains a more plausible option.
We report on the discovery and analysis of the transient X-ray pulsar CXO/XMMU J073709.13+653544 detected in the 2004 August-October Chandra and XMM observations of the nearby spiral galaxy NGC2403. The source exhibits X-ray pulsations with a period P~18 s, a nearly sinusoidal pulse shape and pulsed fraction 46-70%. The source shows a rapid decrease of the pulsation period from 18.25 s on Aug. 9 to 17.93 s on Sep. 12 and 17.56 s on Oct. 3, 2004. The X-ray spectra of the source are hard and are well fitted with an absorbed simple power law of photon index 0.9~1.2. The X-ray properties of the source and the absence of an optical/UV counterpart allow us to identify CXO/XMMU J073709.13+653544 as accreting X-ray pulsar in NGC2403. The maximum unabsorbed luminosity of the source in the 0.3-7 keV range, ~2.6x10e38 erg/s at 3.2 Mpc, is at least 260 times higher than its quiescent luminosity. The corresponding luminosity in the 0.3-100 keV energy range could be as high as ~1.2x10e39 erg/s, assuming the typical pulsar energy spectrum with high-energy cut-off at 10-20 keV. The rate of decrease of the pulsation period of the source (-10e-7 s/s) is the fastest observed among accreting pulsars. The evolution of the pulsation period suggests that it is dominated by the intrinsic spin-up of the compact object. The accretion rate implied by X-ray luminosity of CXO/XMMU J073709.13+653544 could account for the observed spin-up rate, assuming that the X-ray source is powered by disk accretion onto highly magnetized neutron star. Based on the transient behavior and overall X-ray properties of the source, we conclude that it could be an X-ray pulsar belonging to either a Be binary system or a low-mass system similar to GRO J1744-28.
The shifting of spectral lines due to induced correlation effect, discovered first by Wolf for the single scattering case which mimics the Doppler mechanism has been extended and developed further by the present authors known as Dynamic Multiple scattering(DMS). We have explored DMS theory for explaining anomalous redshifts in quasars. Our recent work, based on the statistical analysis of the V\'eron-Cetty data(2003) supports that quasar redshifts fit the overall Hubble expansion law, as in the case of galaxies, for z less than equal to 0.295 but not for higher redshifts, indicating clearly the inadequacy of the Doppler effect as the sole mechanism in explaining the redshifts for high redshift quasars for z greater than equal to 0.295. We found that the redshift posseses an additive, discordant component due to frequency shifting from the correlation induced mechanism which increases gradually for ~ 0.295 < z < 3.0, however, appearing to follow the evolutionary picture of the universe with absolute dependence on the physical characteristics i.e., environmental aspects of the relevant sources through which the light rays pass, after being multiply scattered.
The MOJAVE blazar sample consists of the 133 brightest, most compact AGN in the northern sky, and is selected on the basis of 15 GHz VLBA flux density. Since 1994 we have been gathering VLBA data on the sample to measure superluminal jet speeds and to better understand the parsec$-$scale kinematics of AGN jets. We have obtained 1.4 GHz VLA$-$A configuration data on 57 of these sources to investigate whether the extended luminosity of blazars is correlated with parsec$-$scale jet speed, and also to determine what other parsec$-$scale properties are related to extended morphology, such as optical emission line strength and gamma$-$ray emission. We present images and measurements of the kilo-parsec scale emission from the VLA data, which will be used in subsequent statistical studies of the MOJAVE sample.
The true nature of dark energy remains unclear: It is either a strange fluid in the Universe, with a negative effective pressure, or a breakdown in General Relativity on large scales. This question can only be answered through a suite of different observations as a function of redshift. In this paper, I will briefly review our attempts to achieve this goal using data from the Sloan Digital Sky Survey (SDSS). In particular, I will present new measurements of the Baryon Acoustic Oscillations (BAO) from the SDSS DR5 galaxy redshift survey as well as outline the on-going SDSSII Supernova Survey, which has already detected (in 2005-06) over 300 SN Ia's over the redshift range 0.05<z<0.4. I will also discuss the latest measurements of the Integrated Sachs-Wolfe (ISW) effect that now probe the density of dark energy at z~1.5. All these measurements are still consistent with a lambda-dominated universe.
We report the GMRT detection of HI 21cm absorption from the $z \sim 3.39$ damped Lyman-$\alpha$ absorber (DLA) towards PKS 0201+113, the highest redshift at which 21cm absorption has been detected in a DLA. The absorption is spread over $\sim 115$ km s$^{-1}$ and has two components, at $z = 3.387144 (17)$ and $z = 3.386141 (45)$. The stronger component has a redshift and velocity width in agreement with the tentative detection of Briggs et al. (1997), but a significantly lower optical depth. The core size and DLA covering factor are estimated to be $\lesssim 100$ pc and $f \sim 0.69$, respectively, from a VLBA 328 MHz image. If one makes the conventional assumption that the HI column densities towards the optical and radio cores are the same, this optical depth corresponds to a spin temperature of $\ts \sim [(955 \pm 160) \times (f/0.69)] $ K. However, this assumption may not be correct, given that no metal-line absorption is seen at the redshift of the stronger 21cm component, indicating that this component does not arise along the line of sight to the optical QSO, and that there is structure in the 21cm absorbing gas on scales smaller than the size of the radio core. We model the 21cm absorbing gas as having a two-phase structure with cold dense gas randomly distributed within a diffuse envelope of warm gas. For such a model, our radio data indicate that, even if the optical QSO lies along a line-of-sight with a fortuitously high ($\sim 50$%) cold gas fraction, the average cold gas fraction is low, ($\lesssim 17%$), when averaged over the the spatial extent of the radio core. Finally, the large mismatch between peak 21cm and optical redshifts and the complexity of both profiles makes it unlikely that the $z \sim 3.39$ DLA will be useful in tests of fundamental constant evolution.
We present results from a survey of weak MgII absorbers in the VLT/UVES spectra of 81 QSOs obtained from the ESO archive. In this survey, we identified 112 weak MgII systems within the redshift interval 0.4 < z < 2.4 with 86% completeness down to a rest-frame equivalent width of W_r(2796) = 0.02A, covering a cumulative redshift path length of deltaZ=77.3. From this sample, we estimate that the number of weak absorbers per unit redshift dN/dz increases from 1.06 +/- 0.04 at <z>=1.9 to 1.76 +/- 0.08 at <z>=1.2 and thereafter decreases to 1.51 +/- 0.09 at <z>=0.9 and 1.06 +/- 0.10 at <z>=0.6. Thus we find evidence for an evolution in the population of weak MgII absorbers, with their number density peaking at z=1.2. We also determine the equivalent width distribution of weak systems at <z>=0.9 and <z>=1.9. At 0.4 < z < 1.4, there is evidence for a turnover from a powerlaw of the form n(W_r) \propto W_r^{-1.04} at W_r(2796) < 0.1A. This turnover is more extreme at 1.4 < z < 2.4, where the equivalent width distribution is close to an extrapolation of the exponential distribution function found for strong MgII absorbers. Based on these results, we discuss the possibility that some fraction of weak MgII absorbers, particularly single cloud systems, are related to satellite clouds surrounding strong MgII systems. These structures could also be analogs to Milky Way high velocity clouds. In this context, the paucity of high redshift weak MgII absorbers is caused by a lack of isolated accreting clouds on to galaxies during that epoch.
Quasars are notable for the luminous power they emit across decades in frequency from the far-infrared through hard X-rays; emission at different frequencies emerges from physical scales ranging from AUs to parsecs. Each wavelength regime thus offers a different line of sight into the central engine and a separate probe of outflowing material. Therefore, obtaining a complete accounting of the physical characteristics and kinetic power of quasar winds requires a panchromatic approach. X-ray and infrared studies are particularly powerful for covering the range of interesting physical scales and ionization states of the outflow. We present a stratified wind picture based on a synthesis of multiwavelength research programs designed to constrain the nature of mass ejection from radio-quiet quasars. This wind comprises three zones: the highly ionized shielding gas, the UV broad absorption line wind, and the cold dusty outflow. The primary launching mechanism for the wind likely varies in each zone. While radiative acceleration on resonance lines dominates for the UV absorbing wind, the shielding gas may instead be driven by magnetic forces. Ultraviolet continuum radiative pressure, perhaps coupled with magnetic launching, accelerates a dusty outflow that obscures the inner broad line region in unification schemes.
We present results from our 830 ksec observation of the globular cluster 47 Tucanae with the Chandra X-ray Observatory's High Resolution Camera-S. We limit our analysis here to the 19 previously known, localized millisecond pulsars (MSPs) in the cluster. This work more than doubles the sample of X-ray-detected MSPs observed with sensitivity to rotational variability; it is also the first survey of a large group of radio-discovered MSPs for which no previous X-ray pulsations have been detected and is therefore an unbiased survey of the X-ray properties of radio-discovered MSPs. We find that only 47 Tuc D, O and R show significant pulsations at the >~ 4-sigma level, but there is statistical evidence for rotational variability in five additional MSPs. Furthermore, we constrain the pulsed magnetospheric emission of 7 more MSPs using Monte Carlo simulations. The result is that the majority of the 47 Tuc MSPs are characterized by low pulsed fractions, <~ 50%. In cases where larger pulsed fractions are measured the folded pulse profiles show relatively large duty cycles. When considered with previous spectroscopic studies, this suggests that the X-ray emission arises from the neutron star's heated polar caps, and in some cases, from intra-binary shocks, but generally not directly from the star's magnetosphere. We discuss the impact of these results on our understanding of high energy emission from MSPs.
We have investigated the gamma-ray bursts pulses assumed to arise from relativistically expending fireballs. We find, due to the curvature effect, the evolutionary curve of the raw hardness ratio (when the background count is included) varies significantly, depending on the hardness of a burst. For a soft burst, an upside-down pulse of its raw hardness ratio curve (HRC) would be observed; for a hard burst, its raw HRC shows a pulse-like profile with a sinkage in its decaying phase; for a very hard burst, the raw HRC possesses a pulse-like profile without a sinkage in its decaying phase. For a pulse-like raw HRC as shown in the case of the hard and very hard bursts, its peak would appear in advance of that of the corresponding light curve. We have studied here the HRC of GRB 920216, GRB 920830 and GRB 990816 in detail. The features of the raw HRC expected in the hard burst are observed in these bursts. A fit to the three bursts shows that the curvature effect alone could indeed account for the predicted characteristics of HRCs. In addition, we find that the observed hardness ratio tends to be harder at the beginning of the pulses than what the curvature effect could predict and be softer at the late time of the pulses. We believe this is an evidence showing the existence of intrinsic hard-to-soft radiation.
We present the cosmological distance errors achievable using the baryon acoustic oscillations as a standard ruler. We begin from a Fisher matrix formalism that is upgraded from Seo & Eisenstein (2003). We isolate the information from the baryonic peaks by excluding distance information from other less robust sources. Meanwhile we accommodate the Lagrangian displacement distribution into the Fisher matrix calculation to reflect the gradual loss of information in scale and in time due to nonlinear growth, nonlinear bias, and nonlinear redshift distortions. We then show that we can contract the multi-dimensional Fisher matrix calculations into a 2-dimensional or even 1-dimensional formalism with physically motivated approximations. We present the resulting fitting formula for the cosmological distance errors from galaxy redshift surveys as a function of survey parameters and nonlinearity, which saves us going through the 12-dimensional Fisher matrix calculations. Finally, we show excellent agreement between the distance error estimates from the revised Fisher matrix and the precision on the distance scale recovered from N-body simulations.
We explore the usefulness of future gravitational microlensing surveys in the study of binary properties such as the binary fraction and the distributions of binary separation and mass ratio by using the binary sample detectable through a channel of repeating events. For this, we estimate the rate of repeating microlensing eventstoward the Galactic bulge field based on standard models of dynamical and physical distributions of Galactic matter combined with models of binary separation and mass function. From this, we find that the total number of repeating events expected to be detected from $\sim 4$-year space-based surveys will be $\sim 200$--400, that is $\sim 40$--50 times higher than the rate of current surveys. We find that the high detection rate is due to the greatly improved sensitivity to events associated with faint source stars and low-magnification events. We find that the separation range of the binaries to be covered by the repeating events will extend up to 100 AU. Therefore, the future lensing surveys will provide a homogeneous sample that will allow to investigate the statistical properties of Galactic binaries unbiased by brightness of the binary components.
The gravitational core collapse of a star produces a huge burst of neutrinos of all flavors. A number of detectors worldwide are sensitive to such a burst; its detection would yield information about both particle physics and astrophysics. Sensitivity to all flavors, and ability to tag different interactions, will be key for extraction of information. Here I will survey the capabilities of current and future detectors for detection of supernova neutrinos from the Milky Way and beyond.
We report the results of a diffraction-limited, photometric variability study of the central 5"x5" of the Galaxy conducted over the past 10 years using speckle imaging techniques on the W. M. Keck I 10 m telescope. Within our limiting magnitude of mK < 16 mag for images made from a single night of data, we find a minimum of 15 K[2.2 micron]-band variable stars out of 131 monitored stars. The only periodic source in our sample is the previously identified variable IRS 16SW, for which we measure an orbital period of 19.448 +- 0.002 days. In contrast to recent results, our data on IRS 16SW show an asymmetric phased light curve with a much steeper fall-time than rise-time, which may be due to tidal deformations caused by the proximity of the stars in their orbits. We also identify a possible wind colliding binary (IRS 29N) based on its photometric variation over a few year time-scale which is likely due to episodic dust production. None of the 4 LBV candidates in our sample show the characteristic large increase or decrease in luminosity, however, our time baseline is too short to rule them out as LBVs. Among the remaining variable stars, the majority are early-type stars and three are possibly variable due to line of sight extinction variations. For the 7 OB stars at the center of our field of view that have well-determined 3-dimensional orbits, we see no evidence of flares or dimming of their light, which limits the possibility of a cold, geometrically-thin inactive accretion disk around the supermassive black hole, Sgr A*.
The compact remnants of core collapse supernovae - neutron stars and black holes - have properties that reflect both the structure of their stellar progenitors and the physics of the explosion. In particular, the masses of these remnants are sensitive to the density structure of the presupernova star and to the explosion energy. To a considerable extent, the final mass is determined by the ``fallback'', during the explosion, of matter that initially moves outwards, yet ultimately fails to escape. We consider here the simulated explosion of a large number of massive stars (10 to 100 \Msun) of Population I (solar metallicity) and III (zero metallicity), and find systematic differences in the remnant mass distributions. As pointed out by Chevalier(1989), supernovae in more compact progenitor stars have stronger reverse shocks and experience more fallback. For Population III stars above about 25 \Msun and explosion energies less than $1.5 \times 10^{51}$ erg, black holes are a common outcome, with masses that increase monotonically with increasing main sequence mass up to a maximum hole mass of about 35 \Msun. If such stars produce primary nitrogen, however, their black holes are systematically smaller. For modern supernovae with nearly solar metallicity, black hole production is much less frequent and the typical masses, which depend sensitively on explosion energy, are smaller. We explore the neutron star initial mass function for both populations and, for reasonable assumptions about the initial mass cut of the explosion, find good agreement with the average of observed masses of neutron stars in binaries. We also find evidence for a bimodal distribution of neutron star masses with a spike around 1.2 \Msun (gravitational mass) and a broader distribution peaked around 1.4 \Msun.
Modern investigations of magnetic chemically peculiar stars reveal a variety of complex processes in their atmospheres. Realistic spectrum synthesis modelling of these objects has to take into account anomalous chemical composition, strong magnetic field and chemical stratification. These effects complicate calculation of theoretical spectra, especially when one has to deal with large number of lines and wide spectral regions. To overcome the formidable problem of comparing model and observed spectra for magnetic chemically peculiar stars, a new suite of spectrum synthesis programs was developed. Here we describe in detail the synthesis codes, Synth3 and Synthmag and present examples of their application to various aspects of the peculiar-star surface phenomena. The new codes proved to be reliable tools for the line identification, magnetic field determination, chemical abundance and stratification analysis.
In previous papers we proposed a model that high-frequency quasi-periodic oscillations (QPOs) observed in black-hole and neutron-star X-ray binaries are disk oscillations (inertial-acoustic and/or g-mode oscillations) resonantly excited on warped disks. In this paper we examine whether time variations of the QPOs and their frequency correlations observed in neutron-star X-ray binaries can be accounted for by this disk-oscillation model. By assuming that a warp has a time-dependent precession, we can well describe observed frequency correlations among kHz QPOs and LF QPOs in a wide range of frequencies.
Cool weakly ionized gaseous rotating disk, are considered by many models as the origin of the evolution of protoplanetary clouds. Instabilities against perturbations in such disks play an important role in the theory of the formation of stars and planets. Thus, a hierarchy of successive fragmentations into smaller and smaller pieces as a part of the Kant-Laplace theory of formation of the planetary system remains valid also for contemporary cosmogony. Traditionally, axisymmetric magnetohydrodynamic (MHD), and recently Hall-MHD instabilities have been thoroughly studied as providers of an efficient mechanism for radial transfer of angular momentum, and of density radial stratification. In the current work, the Hall instability against nonaxisymmetric perturbations in compressible rotating fluids in external magnetic field is proposed as a viable mechanism for the azimuthal fragmentation of the protoplanetary disk and thus perhaps initiating the road to planet formation. The Hall instability is excited due to the combined effect of the radial stratification of the disk and the Hall electric field, and its growth rate is of the order of the rotation period.
We present our analysis of the multiwavelength photometric & spectroscopic observations of GRB 060210 and discuss the results in the overall context of current GRB models. All available optical data underwent a simultaneous temporal fit, while X-ray and gamma-ray observations were analysed temporally & spectrally. The results were compared to each other and to possible GRB models. The X-ray afterglow is best described by a smoothly broken power-law with a break at 7.4 hours. The late optical afterglow has a well constrained single power-law index which has a value between the two X-ray indices, though it does agree with a single power-law fit to the X-ray. An evolution of the hardness of the high-energy emission is demonstrated and we imply a minimum host extinction from a comparison of the extrapolated X-ray flux to that measured in the optical. We find that the flaring gamma-ray and X-ray emission is likely due to internal shocks while the flat optical light curve at that time is due to the external shock. The late afterglow is best explained by a cooling break between the optical and X-rays and continued central engine activity up to the time of the break. The required collimation corrected energy of ~ 2x10^52 erg, while at the high end of the known energy distribution, is not unprecedented.
The stratification-driven Hall instability in a weakly ionized polytropic plasma is investigated in the local approximation within an equilibrium Keplerian disk of a small aspect ratio. The leading order of the asymptotic expansions in the aspect ratio is applied to both equilibrium as well as the perturbation problems. The equilibrium disk with an embedded purely toroidal magnetic field is found to be stable to radial, and unstable to vertical short-wave perturbations. The marginal stability surface is found in the space of the local Hall and inverse plasma beta parameters, as well as the free parameter of the model which is related to the total current through the disk. To estimate the minimal values of the equilibrium magnetic field that leads to instability, the latter is constructed as a sum of a current free magnetic field and the simplest approximation for magnetic field created by a distributed electric current.
We consider the issue of hemispherical power asymmetry in the three-year WMAP data, adopting the modulation framework introduced by Spergel et al. (2006), with some improvements and extensions. Important improvements include increased angular resolution, a more accurate likelihood definition, more natural parameter choices, and analysis of single-frequency maps, while the two extensions consist of the explicit evaluation of Bayesian evidence and the assessment of frequentist probabilities. With these tools, we find that the model consisiting of an isotropic CMB sky, modulated by a dipole field, gives a substantially better fit to the observations than the purely isotropic model does, even when including the penalty of a larger prior volume. For the ILC map, the Bayesian log-evidence difference is ~1.8 in favour of the modulated model, and the raw improvement in maximum log-likelihood is 6.1. The best-fit modulation dipole axis points toward (l,b) = (225 deg,-27 deg), and the modulation amplitude is 0.114, in excellent agreement with the results from the first-year analyses. The frequentist probability of obtaining such a high modulation amplitude in an isotropic universe is ~1%. These results are not sensitive to data set or sky cut. In conclusion, the statistical evidence for a power asymmetry anomaly is both substantial and robust, although not decisive, for the currently available data. Increased sky coverage through better foreground handling and full-sky and high-sensitivity polarization maps may shed further light on this issue.
Polarimetry remains a largely unexploited technique in observational X-ray astronomy which could provide insight in the study of the strong gravity and magnetic fields at the core of the Constellation-X observational program. Adding a polarization capability to the Constellation-X instrumentation would be immensely powerful. It would make Constellation the first space observatory to simultaneously measure all astrophysically relevant parameters of source X-ray photons; their position (imaging), energy (spectroscopy), arrival time (timing), and polarization. Astrophysical polarimetry requires sensitive well-calibrated instruments. Many exciting objects are extra-galactic (i.e. faint) and may have small polarization. Recent advances in efficiency and bandpass make it attractive to consider a polarimetry Science Enhancement Package for the Constellation-X mission.
We have developed and tested an antireflection (AR) coating method for silicon lenses at cryogenic temperatures and millimeter wavelengths. Our particular application is a measurement of the cosmic microwave background. The coating consists of machined pieces of Cirlex glued to the silicon. The measured reflection from an AR coated flat piece is less than 1.5% at the design wavelength. The coating has been applied to flats and lenses and has survived multiple thermal cycles from 300 to 4 K. We present the manufacturing method, the material properties, the tests performed, and estimates of the loss that can be achieved in practical lenses.
Using archival X-ray data, we find that the catalog location of the X-ray binary Scutum X-1 (Sct X-1) is incorrect, and that the correct location is that of the X-ray source AX J183528-0737, which is 15' to the west. Our identification is made on the basis of the 112-s pulse period for this object detected in an XMM-Newton observation, as well as spatial coincidence between AX J183528-0737 and previous X-ray observations. Based on the XMM-Newton data and archival RXTE data, we confirm secular spin-down of three observations over 17 years with period derivative Pdot~3.9e-9 s/s, but do not detect a previously reported X-ray iron fluorescence line. We identify a bright (Ks=6.55), red (J-Ks=5.51), optical and infrared counterpart to AX J183528-0737 from 2MASS, a number of mid-IR surveys, and deep optical observations, which we use to constrain the extinction to and distance of Sct X-1. From these data, as well as limited near-IR spectroscopy, we conclude that Sct X-1 is most likely a binary system comprised of a late-type giant or supergiant and a neutron star.
A remarkable correlation is found in radio-loud quasars and BLLacs when the directly observed angular motions, u, of features ejected in the innermost regions of their jets are plotted on logarithmic scales versus the directly observed 15 GHz flux density, S, of their central engines: an abrupt upper envelope cut-off with a slope of 0.5 is obtained. This upper envelope and slope can be explained in a simple non-relativistic ejection model if (a), radio-loud quasars are radio standard candles and (b), for the sources defining the cut-off, the features are all ejected with similar speeds. The upper envelope is then due to the maximum projected velocity seen when the accretion disk is edge-on, and ejections are in the plane of the sky. In our simple ejection model, where S is a good measure of relative distance, the observed distribution of angular motions can be explained if the radio luminosity of the source is a function of viewing angle, increasing towards face-on. Here we show that when u is plotted versus redshift, z, the same upper envelope cut-off is seen. It is not as sharply defined, since, in this simple model, the u upper envelope will be smeared out by sources lying at different cosmological distances, z_(c). Normalizing all sources to the same distance (1 Jy) using the flux density, S, removes this smearing and improves the sharpness of the upper envelope, supporting our assumption that S is a measure of relative distance. In this model the redshift of quasars cannot be a reliable indication of their distance. (abridged)
In a previous work, Ulysses data was analyzed to build a complete axisymmetric MHD solution for the solar wind at minimum including rotation and the initial flaring of the solar wind in the low corona. This model has some problems in reproducing the values of magnetic field at 1 AU despite the correct values of the velocity. Here, we intend to extend the previous analysis to another type of solutions and to improve our modelling of the wind from the solar surface to 1 AU. We compare the previous results to those obtained with a fully helicoidal model and construct a hybrid model combining both previous solutions, keeping the flexibility of the parent models in the appropriate domain. From the solar surface to the Alfven, point, a three component solution for velocity and magnetic field is used, reproducing the complex wind geometry and the well-known flaring of the field lines observed in coronal holes. From the Alfven radius to 1 AU and further, the hybrid model keeps the latitudinal dependences as flexible as possible, in order to deal with the sharp variations near the equator and we use the helicoidal solution, turning the poloidal streamlines into radial ones. Despite the absence of the initial flaring, the helicoidal model and the first hybrid solution suffer from the same low values of the magnetic field at 1 AU. However, by adjusting the parameters with a second hybrid solution, we are able to reproduce both the velocity and magnetic profiles observed by Ulysses and a reasonable description of the low corona, provided that a certain amount of energy deposit exists along the flow. The present paper shows that analytical axisymmetric solutions can be constructed to reproduce the solar structure and dynamics from 1 solar radius up to 1 AU.
We report on optical and NIR observations obtained during and after the 2004 December discovery outburst of the X-ray transient and accretion-powered millisecond pulsar IGR J00291+5934. Our observations monitored the evolution of the brightness and the spectral properties of J00291 during the outburst decay towards quiescence. We also present optical, NIR and Chandra observations obtained during true quiescence. Photometry of the field during outburst reveals an optical and NIR counterpart that brightened from R~23 to R~17 and from K=19 to K~16. Spectral analysis of the RIJHK broadband photometry shows excess in the NIR bands that may be due to synchrotron emission. The Halpha emission line profile suggests the orbital inclination is ~22-32 degrees. The preferred range for the reddening towards the source is 0.7 < E(B-V) < 0.9, which is equivalent to 4.06E21 cm^-2 < NH < 5.22E21 cm^-2. The Chandra observations of the pulsar in its quiescent state gave an unabsorbed 0.5-10 keV flux for the best-fitting power-law model to the source spectrum of (7.0 +/- 0.9)E-14 ergs/cm^2/s (adopting a hydrogen column of 4.6E21 cm^-2. The fit resulted in a power-law photon index of 2.4 +/- 0.5. The (R-K)o color observed during quiescence supports an irradiated donor star and accretion disk. We estimate a distance of 2 to 4 kpc towards J00291 by using the outburst X-ray light curve and the estimated critical X-ray luminosity necessary to keep the outer parts of the accretion disk ionized. Using the quiescent X-ray luminosity and the spin period, we constrain the magnetic field of the neutron star to be < 3E8 Gauss.
We revisit the longstanding question of whether first brightest cluster
galaxies are statistically drawn from the same distribution as other cluster
galaxies or are "special", using the new non-parametric, empirically based
model presented in Vale&Ostriker (2006) for associating galaxy luminosity with
halo/subhalo masses. We introduce scatter in galaxy luminosity at fixed halo
mass into this model, building a conditional luminosity function (CLF) by
considering two possible models: a simple lognormal and a model based on the
distribution of concentration in haloes of a given mass. We show that this
model naturally allows an identification of halo/subhalo systems with groups
and clusters of galaxies, giving rise to a clear central/satellite galaxy
distinction.
We then use these results to build up the dependence of brightest cluster
galaxy (BCG) magnitudes on cluster luminosity, focusing on two statistical
indicators, the dispersion in BCG magnitude and the magnitude difference
between first and second brightest galaxies. We compare our results with two
simple models for BCGs: a statistical hypothesis that the BCGs are drawn from a
universal distribution, and a cannibalism scenario merging two galaxies from
this distribution. The statistical model is known to fail from work as far back
as Tremaine&Richstone (1977). We show that neither the statistical model nor
the simplest possibility of cannibalism provide a good match for observations.
Our CLF models both give similar results, in good agreement with observations.
Specifically, we find <m_1> between -25 and -25.5 in the K-band,
sigma(m_1)~0.25 and <Delta_12> between 0.6 and 0.8, for cluster luminosities in
the range of 10^12 to 10^13 h^-2 L_sun.
The Hough transformation has been used successfully for more than four
decades. Originally used for tracking particle traces in bubble chamber images,
this work shows a novel approach turning the initial idea into a powerful tool
to incoherently detect millisecond pulsars in binary orbits.
This poster presents the method used, a discussion on how to treat the time
domain data from radio receivers and create the input "image" for the Hough
transformation, details about the advantages and disadvantages of this
approach, and finally some results from pulsars in 47 Tucanae.
GCRT J1745-3009 is a transient bursting radio source located in the direction of the Galactic center. It was discovered in a 330 MHz VLA observation from 2002 September 30--October 1 and subsequently rediscovered in a 330 MHz GMRT observation from 2003 September 28 by Hyman et al. Here we report a new radio detection of the source in 330 MHz GMRT data taken on 2004 March 20. The observed properties of the single burst detected differ significantly from those measured previously, suggesting that GCRT J1745-3009 was detected in a new physical state. The 2004 flux density was ~0.05 Jy, ~10x weaker than the single 2003 burst and ~30x weaker than the five bursts detected in 2002. We derive a very steep spectral index, alpha = -13.5 +/- 3.0, across the bandpass, a new result previously not detectable due to limitations in the analysis of the 2002 and 2003 observations. Also, the burst was detected for only ~2 min., in contrast to the 10 min. duration observed in the earlier bursts. Due to sparse sampling, only the single burst was detected in 2004, as in the 2003 epoch, and we cannot rule out additional undetected bursts that may have occurred with the same ~77 min. periodicity observed in 2002 or with a different periodicity. Considering our total time on source throughout both our archival and active monitoring campaigns, we estimate the source exhibits detectable bursting activity ~7% of the time.
Relational databases (DBs) are ideal tools to manage bulky and structured
data archives. In particular for Astronomy they can be used to fulfill all the
requirements of a complex project, i.e. the management of: documents, software
(s/w) packages and logs, observation schedules, object catalogues, quick-look,
simulated, raw and processed data, etc. All the information gathered in a
relational DB is easily and simultaneously accessible either from an
interactive tool or a batch program. The user does not need to deal with
traditional files I/O or editing, but has only to build the appropriate (SQL)
query which will return the desired information/data, eventually producing the
aforementioned files or even plots, tables, etc. in a variety of formats. What
is then important for a generic user is to have the tools to easily and quickly
develop, in any desired programming language, the custom s/w which can
import/export the information into/from the DB. An example could be a Web
interface which presents the available data and allows the user to
select/retrieve (or even process) the data subset of interest.
In the last years we have been implementing a package called MCS (see
dedicated paper in this proceedings) which allows users to interact with MySQL
based DBs through any programming language. MCS has a multi-thread (socket)
architecture which means that several clients can submit queries to a server
which in turn manages the communication with the MySQL server and other MCS
servers. Here we'll focus on a the real-world case of the robotic IR-optical
telescope REM (placed at La Silla, Chile) which performs real time images
acquisition, processing and archiving by using some of the MCS capabilities.
I present a brief review of theory of winds in active galactic nuclei (AGN). Magnetic, radiation, and thermal driving likely operate in AGN. In many cases, it is difficult to distinguish, both from observational and theoretical point of view, which of these wind driving mechanisms dominates in producing winds. Therefore, I focus on specific theoretical predictions which could help to improve our understanding of the physics of AGN winds.
The Pulsar Virtual Observatory will provide a means for scientists in all fields to access and analyze the large data sets stored in pulsar surveys without specific knowledge about the data or the processing mechanisms. This is achieved by moving the data and processing tools to a grid resource where the details of the processing are seen by the users as abstract tasks. By developing intelligent scheduling middle-ware the issues of interconnecting tasks and allocating resources are removed from the user domain. This opens up large sets of radio time-series data to a wider audience, enabling greater cross field astronomy, in line with the virtual observatory concept. Implementation of the Pulsar Virtual Observatory is underway, utilising the UK National Grid Service as the principal grid resource.
Today's astronomical projects need computational systems capable to store and analyze large amounts of scientific data, to effectively share data with other research Institutes and to easily implement information services to present data for different purposes (scientific, maintenance, outreach, etc.). Due to the wide scenario of astronomical projects there isn't yet a standardized approach to implement the software needed to support all the requirements of a project. The new approach we propose here is the use of a unified model where all data are stored into the same data base becoming available in different forms, to different users with different privileges.
We report the results of simultaneous observations of the Vela pulsar in X-rays and radio from the RXTE satellite and the Mount Pleasant Radio Observatory in Tasmania. We sought correlations between the Vela's X-ray and radio flux densities and radio arrival times on a pulse by pulse basis. We found significantly higher flux density in Vela's main X-ray peak during radio pulses that arrived early. This excess flux shifts to the 'trough' following the 2nd X-ray peak during radio pulses that arrive later. We suggest that the mechanism producing the radio pulses is intimately connected to the mechanism producing X-rays. Current models using resonant absorption in the outer magnetosphere as a cause of the radio emission, and less directly of the X-ray emission, are explored as a possible explanation for the correlation.
We present results from multi-epoch spectral analysis of XMM-Newton and Chandra observations of the mini broad absorption line (BAL) quasar PG 1115+080. This is one of the few X-ray detected mini-BAL quasars to date that is bright enough in the X-ray band, mostly due to large gravitational-lensing magnifications, to allow in-depth spectral analysis. The present XMM-Newton observations of PG 1115+080 have provided the highest signal-to-noise X-ray spectra of a mini-BAL quasar obtained to date. By modeling the spectra of PG 1115+080 we have obtained constraints on the column density and ionization state of its outflowing absorbing gas. A comparison between these constraints over several epochs indicates significant variability in the properties of the outflowing absorbers in PG 1115+080. The depths of the high-energy broad absorption features in PG 1115+080 show a significant decrease between the first two observation epochs separated by a rest-frame timescale of ~ 1 year. This variability supports the intrinsic nature of these absorbers. Assuming the interpretation that the high-energy absorption features arise from highly ionized Fe XXV we constrain the fraction of the total bolometric energy released by quasars PG 1115+080 and APM 08279+5225 into the IGM in the form of kinetic energy to be epsilon_k = 0.64(-0.40,+0.52) (68% confidence), and epsilon_k =0.09(-0.05,+0.07), respectively. According to recent theoretical studies this range of efficiencies is large enough to influence significantly the formation of the host galaxy and to regulate the growth of the central black hole.
Pulse-to-pulse intensity variations are a common property of pulsar radio emission. For some of the objects single pulses are often 10-times stronger than their average pulse. The most dramatic events are so-called giant radio pulses (GRPs). They can be thousand times stronger than the regular single pulses from the pulsar. Giant pulses are a rare phenomenon, occurring in very few pulsars which split into two groups. The first group contains very young and energetic pulsars like the Crab pulsar, and its twin (PSR B0540-69) in the Large Magellanic Cloud (LMC), while the second group is represented by old, recycled millisecond pulsars like PSR B1937+21, PSR B1821-24, PSR B1957+20 and PSR J0218+4232 (the only millisecond pulsar detected in gamma-rays). We compare the characteristics of GRPs for these two pulsar groups. Moreover, our latest findings of new features in the Crab GRPs are presented. Analysis of our Effelsberg data at 8.35 GHz shows that GRPs do occur in all phases of its ordinary radio emission, including the phases of the two high frequency components (HFCs) visible only between 5 and 9 GHz.
The Parkes Multibeam Survey led to the identification of a number of long-period radio pulsars with magnetic field well above the 'quantum critical field' of ~ 4.4x10^13 G (HBRPs). The HBRPs have similar spin parameters to magnetars, but their emission properties are different, and contradict those theories that predict that radio emission should be suppressed above this critical field. Our observations support the suggestion that initial neutron star spin periods depend on their magnetic fields; in particular, there is a tendency for high-field systems to be born as slow rotators. The aim of this project is to understand the emission properties of HBRPs, using multiple radio frequencies and high time resolution data. One specific objective is to identify HBRPs radio emission characteristics that are different from those of normal pulsars.
We perform a brief census of velocities of isolated versus binary millisecond pulsars. We find the velocities of the two populations are indistinguishable. However, the scale height of the binary population is twice that of the isolated population and the luminosity functions of the two populations are different. We suggest that the scale height difference may be an artifact of the luminosity difference. We examine the magnetic fields of the two populations as a possible source of the luminosity difference.
We present an extraordinary variation of the X-ray spectrum of the obscured AGN in NGC 1365, which was observed by Chandra to change from Compton-thin to Compton-thick and back to Compton-thin in four days. This fast variation imply a a size of ~10^14 cm for the emitting region, and an extremely compact size (~10^16 cm) of the clumpy circumnuclear absorber.
We review some of the main physical and statistical properties of the X-ray absorber in AGNs. In particular, we review the distribution of the absorbing column density inferred from X-ray observations of various AGN samples. We discuss the location of the X-ray absorber and the relation with the dust absorption at optical and infrared wavelengths. Finally, we shortly review the recent findings on X-ray absorption at high luminosities and at high redshift.
We use high resolution spectra obtained with FUSE and STIS to obtain interstellar column densities of H I, D I, O I, S II, Fe II and P II toward the QSO HE 0226-4110 ( l = 253.4 deg , b = -65.77 deg). We obtain D/H = 21(+8, -6) ppm. Correcting for a small amount of contamination from D and H in the Local Bubble, we obtain D/H = 22 (+8, -6) for the warm neutral medium of the lower Galactic halo. The medium has [O/H] = 0.12(+0.41, -0.20) and [Fe/H] = -1.01 (+0.10, -0.09). This suggests the abundances in the halo toward HE 0226-4110 are not affected by the infall of low metallicity gas and that the gas originates in the disk and is elevated into the halo by energetic processes which erode but do not totally destroy the dust grains. We compare our result to measured values of D/H in other astrophysical sites. The value we measure in the halo gas is consistent with the hypothesis that for many Galactic disk lines of sight D is incorporated into dust. The high average value of D/H = 23.1+/-2.4 ppm measured along 5 sight lines through disk gas in the Solar neighborhood is similar to D/H in the lower Galactic halo. These observations imply the abundance of deuterium in the Galaxy has only been reduced by a factor of 1.12+/-0.13 since its formation.