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Astrophysics

astro-ph new abstracts, Tue, 21 Mar 06 01:00:12 GMT
0603483 -- 0603540 received

astro-ph/0603483 [abs, ps, pdf, other] :

Title: Detecting shock waves in cosmological smoothed particle hydrodynamics simulations
Authors: Christoph Pfrommer (1,2), Volker Springel (1), Torsten A. Ensslin (1), Martin Jubelgas (1) ((1) MPA, (2) CITA)
Comments: 20 pages, 7 figures, just appeared in MNRAS, full resolution version available at this http URL
Journal-ref: MNRAS, 2006, 367, 113

We develop a formalism for the identification and accurate estimation of the strength of structure formation shocks during cosmological smoothed particle hydrodynamics simulations. Shocks not only play a decisive role for the thermalization of gas in virialising structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. Our formalism is applicable both to ordinary non-relativistic thermal gas, and to plasmas composed of CRs and thermal gas. To this end, we derive an analytical solution to the one-dimensional Riemann shock tube problem for a composite plasma of CRs and thermal gas. We apply our methods to study the properties of structure formation shocks in high-resolution hydrodynamic simulations of the LCDM model. We find that most of the energy is dissipated in weak internal shocks with Mach numbers M~2 which are predominantly central flow shocks or merger shock waves traversing halo centres. Collapsed cosmological structures are surrounded by external shocks with much higher Mach numbers up to M~1000, but they play only a minor role in the energy balance of thermalization. We show that after the epoch of cosmic reionisation the Mach number distribution is significantly modified by an efficient suppression of strong external shock waves due to the associated increase of the sound speed of the diffuse gas. Invoking a model for CR acceleration in shock waves, we find that the average strength of shock waves responsible for CR energy injection is higher than that for shocks that dominate the thermalization of the gas. When combined with radiative dissipation and star formation, our formalism can also be used to study CR injection by supernova shocks, or to construct models for shock-induced star formation in the interstellar medium. (abridged)

 

astro-ph/0603484 [abs, ps, pdf, other] :

Title: Cosmic ray physics in calculations of cosmological structure formation
Authors: Torsten A. Ensslin (1), Christoph Pfrommer (1,2), Volker Springel (1), Martin Jubelgas (1) ((1) MPA, (2) CITA)
Comments: submitted to A&A, 18 pages, 5 figures

Cosmic rays (CRs) play a decisive role within our own Galaxy. They provide partial pressure support against gravity, they trace past energetic events such as supernovae, and they reveal the underlying structure of the baryonic matter distribution through their interactions. To study the impact of CRs on galaxy and cosmic structure formation and evolution, we develop an approximative framework for treating dynamical and radiative effects of CRs in cosmological simulations. Our guiding principle is to try to find a balance between capturing as many physical properties of CR populations as possible while at the same time requiring as little extra computational resources as possible. We approximate the CR spectrum of each fluid element by a single power-law, with spatially and temporally varying normalisation, low-energy cut-off, and spectral index. Principles of conservation of particle number, energy, and pressure are then used to derive evolution equations for the basic variables describing the CR spectrum, both due to adiabatic and non-adiabatic processes. The processes considered include compression and rarefaction, CR injection via shocks in supernova remnants, injection in structure formation shock waves, in-situ re-acceleration of CRs, CR spatial diffusion, CR energy losses due to Coulomb interactions, ionisation losses, Bremsstrahlung losses, and, finally, hadronic interactions with the background gas, including the associated gamma-ray and radio emission due to subsequent pion decay. We show that the formalism reproduces CR energy densities, pressure, and cooling rates with an accuracy of ~10% in steady state conditions where CR injection balances cooling. Our framework is therefore well suited to be included into numerical simulation schemes of galaxy and structure formation. (abridged)

 

astro-ph/0603485 [abs, ps, pdf, other] :

Title: Cosmic ray feedback in hydrodynamical simulations of galaxy formation
Authors: Martin Jubelgas (1), Volker Springel (1), Torsten A. Ensslin (1), Christoph Pfrommer (1,2) ((1) MPA, (2) CITA)
Comments: submitted to A&A, 36 pages, 27 figures (partially in reduced resolution)

It is well known that cosmic rays (CRs) contribute significantly to the pressure of the interstellar medium in our own Galaxy, suggesting that they may play an important role in regulating star formation during the formation and evolution of galaxies. We here discuss a novel numerical treatment of the physics of CRs and its implementation in the parallel smoothed particle hydrodynamics code GADGET-2. In our methodology, the non-thermal CR population of each gaseous fluid element is approximated by a simple power law spectrum in particle momentum, characterized by an amplitude, a cut-off, and a fixed slope. Adiabatic compression, and a number of physical source and sink terms are modelled which modify the CR pressure of each particle. The most important sources considered are injection by supernovae and diffusive shock acceleration, while the primary sinks are thermalization by Coulomb interactions, and catastrophic losses by hadronic interactions. We also include diffusion of CRs. Our scheme allows us to carry out the first cosmological structure formation simulations that self-consistently account for CR physics. In simulations of isolated galaxies, we find that CRs can significantly reduce the star formation efficiencies of small galaxies, with virial velocities below \~80 km/s, an effect that becomes progressively stronger towards low mass scales. In cosmological simulations at high redshift, the total mass-to-light ratio of small halos and the faint-end of the luminosity function are strongly affected. When CR acceleration in shocks is followed as well, up to ~40% of the energy dissipated at structure formation shocks can appear as CR pressure at z~3-6, but this fraction drops to ~10% at low redshifts when the shock distribution becomes increasingly dominated by lower Mach numbers. (abridged)

 

astro-ph/0603486 [abs, ps, pdf, other] :

Title: Willman 1 - A Galactic Satellite at 40 kpc With Multiple Stellar Tails
Authors: Beth Willman, Morad Masjedi, David W. Hogg, Julianne J. Dalcanton, David Martinez-Delgado, Michael Blanton, Andrew A. West, Aaron Dotter, Brian Chaboyer
Comments: 10 pages, 4 figures. Submitted to AJ

SDSSJ1049+5103, commonly known as Willman 1, is an extremely low-luminosity Milky Way companion whose properties are intermediate between those of globular clusters and dwarf spheroidals. In this paper, we use deep photometry to show that this object is old and moderately metal-poor, has a distance of 38 +/- 7 kpc, has an M_V of -2.5 mag, and has a half-light radius of 21 +/- 7 pc, consistent with previous estimates. The spatial distribution of Willman 1's main sequence stars shows 1) its total spatial extent exceeds its tidal radius for a range of assumptions about its total mass and its orbit and 2) the presence of prominent multi-directional stellar tails. The tidal interactions causing these tail features may explain the large physical size of Willman 1 relative to low-luminosity globular clusters. It is the most distant Galactic object yet known to display prominent tails, and is the only distant satellite to display multi-directional tails. Although we cannot at present determine the cause of this unusual morphology, preliminary comparisons between the morphology of Willman 1 and published simulations suggest that it may be near the apocenter of its orbit, or that it may have interacted with another halo object. We find a significant difference between the luminosity functions of stars in the center and in the tails of Willman 1, strongly suggesting mass segregation much like that seen in Palomar 5. Although Willman 1 has more pronounced tidal tails than most confirmed Milky Way dwarf galaxies, because of its very low stellar mass we cannot at present rule out the possibility that it has a dark matter halo. (Abridged)

 

astro-ph/0603487 [abs, ps, pdf, other] :

Title: Growing Live Disks Within Cosmologically Assembling Asymmetric Halos: Washing Out the Halo Prolateness
Authors: Ingo Berentzen (U. of Kentucky) Isaac Shlosman (U. of Kentucky)
Comments: 12 pp, 10 figures, 2 animations. Submitted to the Astrophysical Journal. Animations available at this http URL

We study the growth of galactic disks in live triaxial DM halos. The halos have been assembled through constrained realizations method and evolved from the linear regime using cosmological simulations. The `seed' disks have been inserted at redshift z=3 and increased in mass tenfold over various time periods, ~1-3 Gyr, with the halo responding quasi-adiabatically to this process. We follow the dynamical and secular evolution of the disk-halo system and analyze changes in the most important parameters, like 3-D DM shapes, stellar and DM radial density profiles, stellar bar development, etc. We find that a growing disk is responsible for washing out the halo prolateness and for diluting its flatness over a period of time comparable to the disk growth. Moreover, we find that a disk which contributes more to the overall rotation curve in the system is also more efficient in axisymmetrizing the halo, without accelerating the halo figure rotation. The observational corollary is that the maximal disks probably reside in nearly axisymmetric halos, while disks whose rotation is dominated by the halo at all radii are expected to reside in more prolate halos. The halo shape is sensitive to the final disk mass, but is independent of how the seed disk is introduced into the system. We also expect that the massive disks are subject to a bar instability, while light disks have this instability damped by the halo triaxiality. Implications to the cosmological evolution of disks embedded in asymmetric halos are discussed and so are the corollaries for the observed fraction of stellar bars. Finally, the halo responds to the stellar bar by developing a gravitational wake -- a `ghost' bar of its own which is almost in-phase with that in the disk.

 

astro-ph/0603488 [abs, ps, pdf, other] :

Title: The Spitzer Space Telescope Extra-Galactic First Look Survey: 24 micron data reduction, catalog, and source identification
Authors: Dario Fadda, F. R. Marleau, L. J. Storrie-Lombardi, D. Makovoz, D. T. Frayer, P. N. Appleton, L. Armus, S. C. Chapman (1), P. I. Choi, F. Fang, I. Heinrichsen, G. Helou, M. Im (2), M. Lacy, D. L. Shupe, B. T. Soifer, G. K. Squires, J. Surace, H. I. Teplitz, G. Wilson, L. Yan, (Spitzer Science Center - Caltech expect (1) Dep. of Astronomy - Caltech, (2) Seoul National University.)
Comments: 25 pages, 27 figures. 7 figures are given as png to reduce their size. Paper accepted for publication by AJ (June 2006, vol. 131). Full-resolution version of the paper and machine-readable catalogs are available at this http URL

We present the reduction of the 24 micron data obtained during the first cosmological survey performed by the Spitzer Space Telescope (First Look Survey, FLS). The survey consists of a shallow observation of 2.5x2 sq deg centered at 17h18m +59d30m (main survey) and a deeper observation of 1x0.5 sq deg centered at 17h17m +59d45m(verification survey). Issues with the reduction of the 24 micron MIPS data are discussed and solutions to attenuate instrumental effects are proposed and applied to the data. Approximately 17000 sources are extracted with a SNR greater than five. The photometry of the point sources is evaluated through PSF fitting using an empirical PSF derived from the data. Aperture corrections and the absolute calibration have been checked using stars in the field. Astrometric and photometric errors depend on the SNR of the source varying between 0.35-1 arcsec and 5-15%, respectively, for sources detected at 20-5 sigma. The flux of the 123 extended sources have been estimated through aperture photometry. The extended sources cover less than 0.3% of the total area of the survey. Based on simulations, the main and verification surveys are 50% complete at 0.3 and 0.15 mJy, respectively. Counterparts have been searched for in optical and radio catalogs. More than 80% of the 24 micron sources have a reliable optical counterpart down to R=25.5. 16% of the sources have a 20 cm counterpart down to 0.1 mJy and ~ 80% of the radio-infrared associations have a reliable optical counterpart. A residual map is obtained by subtracting point sources detected at the 3-sigma level and interpolating the regions occupied by extended sources. Several galactic clouds with low and intermediate velocities are identified by comparison with neutral Hydrogen data from this field.

 

astro-ph/0603489 [abs, ps, pdf, other] :

Title: Diffraction of Apodized Pupil Mapping Systems with Aberrations
Authors: Ruslan Belikov, N. Jeremy Kasdin, Robert J. Vanderbei
Comments: 29 pages, 11 figures, submitted to ApJ

Pupil mapping is a promising and unconventional new method for high contrast imaging being considered for terrestrial exoplanet searches. It employs two (or more) specially designed aspheric mirrors to create a high-contrast amplitude profile across the telescope pupil that does not appreciably attenuate amplitude. As such, it reaps significant benefits in light collecting efficiency and inner working angle, both critical parameters for terrestrial planet detection. While much has been published on various aspects of pupil mapping systems, the problem of sensitivity to wavefront aberrations remains an open question. In this paper, we present an efficient method for computing the sensitivity of a pupil mapped system to Zernike aberrations. We then use this method to study the sensitivity of a particular pupil mapping system and compare it to the concentric-ring shaped pupil coronagraph. In particular, we show how contrast and inner working angle degrade with increasing Zernike order and rms amplitude, which has obvious ramifications for the stability requirements and overall design of a planet-finding observatory.

 

astro-ph/0603490 [abs, ps, pdf, other] :

Title: Interstellar Scintillation of PSR J0437-4715
Authors: T.V. Smirnova, C.R. Gwinn, V.I. Shishov
Comments: 9 pages, 3 figures, 2 tables

We studied the turbulence spectrum of the local interstellar plasma in the direction of PSR J0437-4715, on the basis of our observations and those reported earlier by others. We combine these data to form a structure function for the variations of phase along the line of sight to the pulsar. For observations that did not report them, we infer modulation indices from a theoretical model. We find that all of the observations fit a power-law spectrum of turbulence with index n=3.46+/-0.20. We suggest that differences among reported values for scintillation bandwidth and timescale for this pulsar arise from differences in observing parameters. We suggest that refractive effects dominate for this line of sight, with refraction angle about twice the diffraction angle at 330 MHz observing frequency. We suggest that the scattering of this pulsar lies in a layer of enhanced turbulence, about 10 pc from the Sun. We propose that the flux variations of the extragalactic source PKS 0405-385 arise in the same scattering layer.

 

astro-ph/0603491 [abs, ps, pdf, other] :

Title: Local Group Dwarf Galaxies and the Fundamental Manifold of Spheroids
Authors: Dennis Zaritsky (U. Arizona), Anthony H. Gonzalez (U. Florida), Ann I. Zabludoff (U. Arizona)
Comments: accepted for publication in ApJ Letters (5 pages)

The fundamental manifold (FM), an extension of the fundamental plane formalism, incorporates all spheroid-dominated stellar systems from dwarf ellipticals up to the intracluster stellar populations of galaxy clusters by accounting for the continuous variation of the mass-to-light ratio within the effective radius r_e with scale. Here, we find that Local Group dwarf spheroidal and dwarf elliptical galaxies, which probe the FM relationship roughly one decade lower in r_e than previous work, lie on the extrapolation of the FM. When combined with the earlier data, these Local Group dwarfs demonstrate the validity of the empirical manifold over nearly four orders of magnitude in r_e. The continuity of the galaxy locus on the manifold and, more specifically, the overlap on the FM of dwarf ellipticals like M 32 and dwarf spheroidals like Leo II, implies that dwarf spheroidals belong to the same family of spheroids as their more massive counterparts. The only significant outliers are Ursa Minor and Draco. We explore whether the deviation of these two galaxies from the manifold reflects a breakdown in the coherence of the empirical relationship at low luminosities or rather the individual dynamical peculiarities of these two objects. We discuss some implications of our results for how the lowest mass galaxies form.

 

astro-ph/0603492 [abs, ps, pdf, other] :

Title: High-Resolution Absorption Spectroscopy of Multi-phase, High-Metallicity Gas Associated with the Luminous Quasar HE 0226-4110
Authors: Rajib Ganguly, Kenneth R. Sembach, Todd M.Tripp, Blair D. Savage, Bart P. Wakker
Comments: 25 pages, including 14 figures; uses emulateapj.cls document class; accepted for publication in The Astrophysical Journal

We present FUSE and HST/STIS observations of the absorption line system near the emission redshift of the radio-quiet, X-ray bright quasar HE0226-4110 (z = 0.495, V=15.2). The spectra cover the rest-frame wavelength range 610--1150 A, and we detect a wide range of ionization species, including four adjacent stages of oxygen (O III-VI), which reveal a striking change in gas kinematics with ionization. Examination of the O VI 1031, 1037 doublet profiles reveals no evidence for partial coverage or unresolved saturated structure. O III is only detected in a narrow feature which is also traced by H I and C III, suggesting that they arise in the same gas. Absorption at the same velocity is also present in other species N IV, O IV-VI, S IV, and possibly N VIII, but the kinematics differ from the O III, implying production in separate gaseous phases. The H I, O II-IV, and C III information in yield an estimate of both the photoionization parameter and metallicity of the O III-bearing gas: [O/H]=+0.12(-0.03/+0.16), log U=-2.29(-0.23/+0.02). We discuss two possible locations for the gas in this associated absorption-line system: the narrow emission line region of the quasar, and the halo of the quasar host galaxy. An additional narrow (thus, photoionized) component that is only detected in O VI appears 58 km/s redward of the O III-bearing gas with -0.35 < log U < 0.02. Additional structure is detected in the associated absorber in the form of two broad components which only appear in moderate to high ionization species. [highly abridged]

 

astro-ph/0603493 [abs, ps, pdf, other] :

Title: Inverting Color-Magnitude Diagrams to Access Precise Star Cluster Parameters: A Bayesian Approach
Authors: Ted von Hippel, William H. Jefferys, James Scott, Nathan Stein, D. E. Winget, Steven DeGennaro, Albert Dam, Elizabeth Jeffery
Comments: 36 pages, including 17 figures, accepted to ApJ. Higher res versions of fig 15 & 16 available upon request to first author

We demonstrate a new Bayesian technique to invert color-magnitude diagrams of main sequence and white dwarf stars to reveal the underlying cluster properties of age, distance, metallicity, and line-of-sight absorption, as well as individual stellar masses. The advantages our technique has over traditional analyses of color-magnitude diagrams are objectivity, precision, and explicit dependence on prior knowledge of cluster parameters. Within the confines of a given set of often-used models of stellar evolution, the initial-final mass relation, and white dwarf cooling, and assuming photometric errors that one could reasonably achieve with the Hubble Space Telescope, our technique yields exceptional precision for even modest numbers of cluster stars. For clusters with 50 to 400 members and one to a few dozen white dwarfs, we find typical internal errors of sigma([Fe/H]) <= 0.03 dex, sigma(m-M) <= 0.02 mag, and sigma(Av) <= 0.01 mag. We derive cluster white dwarf ages with internal errors of typically only 10% for clusters with only three white dwarfs and almost always <= 5% with ten white dwarfs. These exceptional precisions will allow us to test white dwarf cooling models and standard stellar evolution models through observations of white dwarfs in open and globular clusters.

 

astro-ph/0603494 [abs, ps, pdf, other] :

Title: Massive neutrinos and cosmology
Authors: Julien Lesgourgues, Sergio Pastor
Comments: 120 pages, 23 figures, review article submitted to Physics Reports

The present experimental results on neutrino flavour oscillations provide evidence for non-zero neutrino masses, but give no hint on their absolute mass scale, which is the target of beta decay and neutrinoless double-beta decay experiments. Crucial complementary information on neutrino masses can be obtained from the analysis of data on cosmological observables, such as the anisotropies of the cosmic microwave background or the distribution of large-scale structure. In this review we describe in detail how free-streaming massive neutrinos affect the evolution of cosmological perturbations. We summarize the current bounds on the sum of neutrino masses that can be derived from various combinations of cosmological data, including the most recent analysis by the WMAP team. We also discuss how future cosmological experiments are expected to be sensitive to neutrino masses well into the sub-eV range.

 

astro-ph/0603495 [abs, ps, pdf, other] :

Title: Supernova 2006aj and the associated X-Ray Flash 060218
Authors: J. Sollerman (1,2), A. O. Jaunsen (3), J. P. U. Fynbo (1), J. Hjorth (1), P. Jakobsson (1), M. Stritzinger (1), C. Feron (1), P. Laursen (1), J.-E. Ovaldsen (3), J. Selj (3), C. C. Thone (1), D. Xu (1), T. Davis (1), J. Gorosabel (4), D. Watson (1), R. Duro (3), N. Lysfjord (3), I. Ilyin (5), M. Wold (3), B. L. Jensen (1), S. Walch (7) ((1) Dark Cosmology Centre, Copenhagen (2) Department of Astronomy, Stockholm (3) Institute of theoretical astrophysics, Oslo (4) Instituto de Astrofisica de Andalucia, Granada (5) Astrophysikalisches Institut, Potsdam (6) ESO, Garching (7) University Observatory Munich, Munich)
Comments: This draft was submitted to A&A main journal on February 17, 6 figures, comments welcome

We present optical lightcurves and spectra of the afterglow of the gamma-ray burst (GRB) of February 18, 2006. GRB 060218 is a nearby long GRB which is clearly associated with a supernova - dubbed SN 2006aj. Our optical lightcurves define the rise times, the lightcurve shapes and the absolute magnitudes in the U, V and R bands, and we compare these data with data for other relevant supernovae. SN 2006aj evolved quite fast, somewhat similar to SN 2002ap, but not as fast as SN 1994I. Our spectra show the evolution of the supernova over the peak, when the U-band portion of the spectrum rapidly fades due to extensive line blanketing. We compare to similar spectra of very energetic Type Ic supernovae. Our first spectra are earlier than spectra for any other GRB-SN. The spectrum taken 12 days after burst in the rest frame is similar to somewhat later spectra of both SN 1998bw and SN 2003dh, implying a rapid early evolution. This is consistent with the fast lightcurve. From the narrow emission lines from the host galaxy we derive a redshift of z=0.0331+-0.0007. The flux of these lines indicate a high-excitation state, and a modest metallicity and star formation rate of the host galaxy.

 

astro-ph/0603496 [abs, ps, pdf, other] :

Title: The shortest modulation period Blazhko RR Lyrae star: SS Cnc
Authors: J. Jurcsik, B. Szeidl, Á. Sódor, I. Dékány, Zs. Hurta, K. Posztobányi, K. Vida, M. Váradi, A. Szing
Comments: 23 pages, 9 figures, 2 tables. To appear in AJ

Extended BV(RI)c CCD observations of SS Cnc, a short period RRab star are presented. Nearly 1400 data points in each band have been obtained spanning over 79 days during the spring of 2005. The star exhibits light curve modulation, the so called Blazhko effect with small amplitude (B maximum brightness varies 0.1 mag) and with the shortest modulation period (5.309 d) ever observed. In the Fourier spectrum of the V light curve the pulsation frequency components are detected up to the 24th harmonic order, and modulation side lobe frequencies with significantly asymmetric amplitudes are seen up to the 15th and 9th orders for the lower and higher frequency components, respectively. Detailed comparison of the modulation behavior of SS Cnc and RR Gem, the two recently discovered small amplitude, short modulation period Blazhko stars is presented. The modulation frequency (f_m) appears in the Fourier spectrum of both stars with similar amplitude. We also demonstrate that the modulation frequencies have basically different properties as the pulsation and modulation side lobe frequencies have, indicating that the physics behind these frequency components are not the same. The discovery of small amplitude modulations of RRab stars cautions that the large photometric surveys (MACHO, OGLE) may seriously underestimate the number of modulated RR Lyrae stars.

 

astro-ph/0603497 [abs, ps, pdf, other] :

Title: The Dissipative Merger Progenitors of Elliptical Galaxies
Authors: Avishai Dekel (HU Jerusalem), Thomas, J. Cox (CfA Harvard)
Comments: 9 pages, 4 figures

We address the deviations of the scaling relations of elliptical galaxies from the expectations based on the virial theorem and homology, including the "tilt" of the "fundamental plane" and the steep decline of density with mass. We show that such tilts result from dissipative major mergers once the gas fraction available for dissipation declines with progenitor mass, and derive the scaling properties of the progenitors. We use hydrodynamical simulations to quantify the effects of major mergers with different gas fractions on the structural properties of galaxies. The tilts are driven by the differential shrinkage of the effective stellar radius as a function of dissipation in the merger, while the correlated smaller enhancements in internal velocity and stellar mass keep the slope of the velocity-stellar mass relation near V \pr M_*^{1/4}. The progenitors match a straightforward model of disc formation in LCDM haloes. Their total to stellar mass ratio within the effective radius varies as M/M_* \pr M_*^-0.25, consistent with supernova feedback. They are nearly homologous in the sense that the dark-matter fractions within the effective and virial radii scale with mass in a similar way, with only a weak decline of density with mass. The progenitor radius is roughly R \pr M_*^0.3, compatible with today's intermediate late-type galaxies. This indicates that the latest wet mergers involved relatively big discs. The dissipative gas to stellar mass ratio is predicted to decline \pr M_*^-0.5, similar to the observed trend in today's blue sequence galaxies. Such a trend should be observed in relatively massive gaseous galaxies at z~1-4. The corresponding "baryonic" relations are consistent with homology and spherical virial equilibrium, V \pr R \pr M_b^1/3.

 

astro-ph/0603498 [abs, ps, pdf, other] :

Title: Magnetospheric Accretion in Classical T Tauri Stars
Authors: J. Bouvier, S.H.P. Alencar, T.J. Harries, C.M. Johns-Krull, M.M. Romanova
Comments: PPV conference paper, 16 pages, 10 figures

The inner 0.1 AU around accreting T Tauri stars hold clues to many physical processes that characterize the early evolution of solar-type stars. The accretion-ejection connection takes place at least in part in this compact magnetized region around the central star, with the inner disk edge interacting with the star's magnetosphere thus leading simultaneously to magnetically channeled accretion flows and to high velocity winds and outflows. The magnetic star-disk interaction is thought to have strong implications for the angular momentum evolution of the central system, the inner structure of the disk, and possibly for halting the migration of young planets close to the stellar surface. We review here the current status of magnetic field measurements in T Tauri stars, the recent modeling efforts of the magnetospheric accretion process, including both radiative transfer and multi-D numerical simulations, and summarize current evidence supporting the concept of magnetically-channeled accretion in young stars. We also discuss the limits of the models and highlight observational results which suggest that the star-disk interaction is a highly dynamical and time variable process in young stars.

 

astro-ph/0603499 [abs, ps, pdf, other] :

Title: A Viscous Heating Mechanism for the Hot Plasma in the Galactic Center Region
Authors: R. Belmont, M. Tagger
Comments: 17 pages, 6 figures, accepted for publication in A&A

In addition to lines originating in a soft phase at ~0.8 keV and to cold molecular clouds, the X-ray spectra from the Galactic center region also exhibit properties similar to those of a diffuse, thin, very hot plasma at 8 keV on a scale of hundreds of parsecs. This phase is surprising for more than one reason. First, such a hot plasma should not be bound to the Galactic plane and the power needed to sustain the escaping matter would be higher then any known source. Second, there is no known mechanism able to heat the plasma to more than a few keV. Recently we have suggested that, hydrogen having escaped, the hot plasma could be a helium plasma, heavy enough to be gravitationally confined. In this case, the required power is much more reasonable. We present here a possible heating mechanism which taps the gravitational energy of the molecular clouds. We note that the 8 keV plasma is highly viscous and we show how viscous friction of molecular clouds flowing within the hot phase can dissipate energy in the gas and heat it. We detail the MHD wake of a spherical cloud by considering the different MHD waves the cloud can excite. We find that most of the energy is dissipated by the damping of Alfvenic perturbations in two possible manners, namely by non-linear effects and by a large scale curvature of the field lines. Depending on the field strength, this heating can balance the radiative cooling. We note that the plasma parameters may be optimal to make the dissipation most efficient, suggesting a self-regulation mechanism. The loss of kinetic and gravitational energy also causes accretion of the clouds and may have significant action on the gas dynamics in this region between the large scale, bar dominated flow and the central accretion to the massive black hole.

 

astro-ph/0603500 [abs, ps, pdf, other] :

Title: Carmeli's cosmology fits data for an accelerating and decelerating universe without dark matter nor dark energy
Authors: Firmin J. Oliveira, John G. Hartnett
Comments: 19 pages, 9 figures

A new relation for the density parameter \Omega is derived as a function of expansion velocity v based on Carmeli's cosmology. This density function is used in the luminosity distance relation D_{L}. A heretofore neglected source luminosity correction factor (1-(v/c)^2)^{-1/2} is now included in D_{L}. These relations are used to fit type Ia supernovae (SNe Ia) data, giving consistent, well behaved fits over a broad range of redshift 0.1 < z < 2. The best fit to the data for the local density parameter is \Omega_m = 0.0401 \pm 0.0199. From this local density it is determined that the redshift where the universe expansion transitions from acceleration to deceleration is z_{t}= 1.095 {}^{+0.264}_{-0.155}. Because \Omega_m is within the baryonic budget there is no need for any additional dark matter to account for the SNe Ia redshift luminosity data. And, from the fact that the predicted transition redshift z_{t} is well within the redshift range of the data, there also is no need for any dark energy to account for the expansion rate transition.

 

astro-ph/0603501 [abs, ps, pdf, other] :

Title: New Results from High Energy Gamma-Ray Astronomy
Authors: Heinrich J. Völk
Comments: 10 pages, 6 figures, Invited paper at IAU Symposium No.230, 2005, in Dublin (Ireland); E.J.A. Meurs, G. Fabbiano, eds.; in press (2006)

High energy gamma-ray astronomy has recently made significant progresss through ground-based instruments like the {\it H.E.S.S.} array of imaging atmospheric Cherenkov telescopes. The unprecedented angular resolution and the large field of view has allowed to spatially resolve for the first time the morphology of gamma-ray sources in the TeV energy range. The experimental technique is described and the types of sources detected and still expected are discussed. Selected results include objects as different as a Galactic binary Pulsar, the Galactic Center and Supernova Remnants but they also concern the diffuse extragalactic optical/infrared radiation field. Finally, a scan of the Galactic plane in TeV gamma rays is described which has led to a significant number of new TeV sources, many of which are still unidentified in other wavelengths. The field has a close connection with X-ray astronomy which allows the study of the synchrotron emission from these very high energy sources.

 

astro-ph/0603502 [abs, ps, pdf, other] :

Title: Shell-type Supernova Remnants
Authors: Heinrich J. Völk
Comments: 17 pages, 10 Figures, Invited paper at conference ``Cherenkov 2005'', Towards a Network of Atmospheric Cherenkov Detectors VII, at Ecole Polytechnique, Palaiseau (France), April 27-29, 2005; Editors: B. Degrange, G. Fontaine, pp. 233-245 (2006)

The role of Supernova Remnants (SNRs) for the production of the Galactic Cosmic Rays is reviewed from the point of view of theory and very high energy gamma-ray experiments. The point is made that theory can describe young SNRs very well, if the evidence from the synchrotron emission is used to empirically determine several parameters of the theory, and thus theory can predict the relative contributions of hadronic and leptonic gamma rays at TeV energies. This is exemplified for several objects that have been observed intensively during the last years. Future key observations are discussed.

 

astro-ph/0603503 [abs, ps, pdf, other] :

Title: Slow evolution of elliptical galaxies induced by dynamical friction
Authors: S.E. Arena, G. Bertin, T. Liseikina, F. Pegoraro
Comments: 13 pages, 5 figures, Accepted for publication in A&A

Many astrophysical problems, ranging from structure formation in cosmology to dynamics of elliptical galaxies, refer to slow processes of evolution of essentially collisionless self-gravitating systems. In order to determine the relevant quasi-equilibrium configuration at time t from given initial conditions, it is often argued that such slow evolution may be approximated in terms of adiabatic evolution, for the calculation of which efficient semi--analytical techniques are available. Here we focus on the slow process of evolution, induced by dynamical friction of a host stellar system on a minority component of "satellites", that we have investigated in a previous paper, to determine to what extent an adiabatic description might be applied. The study is realized by comparing directly N--body simulations of the stellar system evolution (in two significantly different models) from initial to final conditions in a controlled numerical environment. We demonstrate that for the examined process the adiabatic description is going to provide incorrect answers, not only quantitatively, but also qualitatively. The two classes of models considered exhibit generally similar trends in evolution, with one exception noted in relation to the evolution of the total density profile. This simple conclusion should be taken as a warning against the indiscriminate use of adiabatic growth prescriptions in studies of structure of galaxies.

 

astro-ph/0603504 [abs, ps, pdf, other] :

Title: Near-Infrared Photometry of Carbon Stars
Authors: Patricia A. Whitelock, Michael W. Feast, Freddy Marang, M.A.T. Groenewegen
Comments: 35 pages, 21 figs, accepted for publication in MNRAS. Large data table will be available on-line only

Near-infrared, JHKL, photometry of 239 Galactic carbon-rich variable stars is presented and discussed. From these and published data the stars were classified as Mira or non-Mira variables and amplitudes and pulsation periods, ranging from 222 to 948 days for the Miras, were determined for most of them. A comparison of the colour and period relations with those of similar stars in the Large Magellanic Cloud indicates minor differences, which may be the consequence of sample selection effects. Apparent bolometric magnitudes were determined by combining the mean JHKL fluxes with mid-infrared photometry from IRAS and MSX. Then, using the Mira period luminosity relation to set the absolute magnitudes, distances were determined -- to greater accuracy than has hitherto been possible for this type of star. Bolometric corrections to the K magnitude were calculated and prescriptions derived for calculating these from various colours. Mass-loss rates were also calculated and compared to values in the literature.
Approximately one third of the C-rich Miras and an unknown fraction of the non-Miras exhibit apparently random obscuration events that are reminiscent of the phenomena exhibited by the hydrogen deficient RCB stars. The underlying cause of this is unclear, but it may be that mass loss, and consequently dust formation, is very easily triggered from these very extended atmospheres.

 

astro-ph/0603505 [abs, ps, pdf, other] :

Title: Carbon-Rich Mira Variables: Radial Velocities and Distances
Authors: John W. Menzies, Michael W. Feast, Patricia A. Whitelock
Comments: 11 pages, accepted for publication in MNRAS

Optical radial velocities have been measured for 38 C-type Mira variables. These data together with others in the literature are used to study the differences between optical and CO mm observations for C-Miras and the necessary corrections to the optical velocities are derived in order to obtain the true radial velocities of the variables. The difference between absorption and emission line velocities is also examined. A particularly large difference (+30 km\s) is found in the case of the H-alpha emission line. A catalogue is given of 177 C-Miras with estimated distances and radial velocities. The distances are based on bolometric magnitudes derived in Paper I using SAAO observations or (for 60 of the stars) using non-SAAO photometry. In the latter case the necessary transformations to the SAAO system are derived. These data will be used in paper III to study the kinematics of the C-Miras.

 

astro-ph/0603506 [abs, ps, pdf, other] :

Title: Carbon-Rich Mira Variables: Kinematics and Absolute Magnitudes
Authors: Michael W. Feast, Patricia A. Whitelock, John W. Menzies
Comments: 8 pages, 2 figures, accepted for publication in MNRAS

The kinematics of galactic C-Miras are discussed on the basis of the bolometric magnitudes and radial velocities of Papers I and II of this series. Differential galactic rotation is used to derive a zero-point for the bolometric period-luminosity relation which is in satisfactory agreement with that inferred from the LMC C-Miras. We find for the galactic Miras, Mbol = -2.54logP + 2.06 (+/- 0.24), where the slope is taken from the LMC. The mean velocity dispersion, together with the data of Nordstroem et al. and the Padova models, leads to a mean age for our sample of C-Miras of 1.8 +/- 0.4 Gyr and a mean initial mass of 1.8 +/-0.2 solar masses. Evidence for a variation of velocity dispersion with period is found, indicating a dependence of period on age and initial mass, the longer period stars being younger. We discuss the relation between the O- and C-Miras and also their relative numbers in different systems.

 

astro-ph/0603507 [abs, ps, pdf, other] :

Title: Indirect signatures for axion(-like) particles
Authors: K. Zioutas, K. Dennerl, M. Grande, D.H.H. Hoffmann, J. Huovelin, B. Lakic, S. Orlando, A. Ortiz, Th. Papaevangelou, Y. Semertzidis, Sp. Tzamarias, O. Vilhu
Comments: 9 pages, 2 Figures, TAUP2005 conf. proc. (extended version)

Magnetic field dependent transient solar observations are suggestive for axion-photon oscillations with light axion(-like) particle involvement. Novel dark-moon measurements with the SMART X-ray detectors can be conclusive for radiatively decaying massive exotica like the generic solar Kaluza-Klein axions. Furthermore, the predicted intrinsic strong solar magnetic fields could be the reason of enhanced low energy axion production. Such an axion component could be the as yet unknown origin of the strong quiet Sun X-ray luminosity at energies below 1 keV. Solar axion telescopes should lower their threshold, aiming to copy processes that might occur near the solar surface, be it due to spontaneous or magnetically induced radiative decay of axion(-like) particles. This is motivated also by the recent claim of an axion-like particle detection by the laser experiment PVLAS.

 

astro-ph/0603508 [abs, ps, pdf, other] :

Title: Past and Future of CG J1720-67.8: Constraints from Observations and Models
Authors: S. Temporin (1,2), W. Kapferer (2) ((1) INAF-Brera Astronomical Observatory, (2) Institute of Astro- and Particle Physics, Univ. Innsbruck)
Comments: 5 pages, 3 (degraded) figures. Proc. ESO Workshop "Groups of galaxies in the nearby Universe", Santiago, Chile, 5-9 Dec. 2005, ESO Astrophysics Symposia, eds. I. Saviane, V. Ivanov & J. Borissova, Springer-Verlag

We discuss the evolution of the peculiar, nearby (z = 0.045), compact galaxy group CG J1720-67.8, by interpreting a large amount of observational information on the basis of our recent results from spectrophotometric evolutionary synthesis models and new N-body/SPH simulations. The group, that is composed of two spiral galaxies with a mass ratio approximately 4:1 and an S0 galaxy in a particularly compact configuration, is undergoing an active pre-merging phase. Several tidal features are signposts of the complex dynamics of the system. We suggest that the observed structure of the tidal features can be explained only if all three galaxies are involved in a strong interaction process.

 

astro-ph/0603509 [abs, ps, pdf, other] :

Title: Mass spectrum of primordial black holes from inflationary perturbation in the Randall-Sundrum braneworld: a limit on blue spectra
Authors: Yuuiti Sendouda (1), Shigehiro Nagataki (2), Katsuhiko Sato (1) ((1) University of Tokyo, (2) Kyoto University)
Comments: 19 pages, 6 figures

The mass spectrum of the primordial black holes formed by density perturbation in the radiation-dominated era of the Randall-Sundrum type-2 cosmology is given. The spectrum coincides with standard four-dimensional one on large scales but the deviation is apparent on smaller scales. The mass spectrum is initially softer than standard four-dimensional one, while after accretion during the earliest era it becomes harder than that. We also show expected extragalactic diffuse photon background spectra varying the initial perturbation power-law power spectrum and give constraints on the blue spectra and/or the reheating temperature. The most recent observations on the small scale density perturbation from WMAP, SDSS and Lyman-\alpha Forest are used. What we get are interpreted as constraints on the smaller scale inflation on the brane connected to the larger one at the scale of Lyman-\alpha Forest. If we set the bulk curvature radius to be 0.1 mm and assume the reheating temperature is higher than 10^6 GeV, the scalar spectral index from the smaller scale inflation is constrained to be n \lesssim 1.3. Typically, the constraints are tighter than standard four-dimensional one, which is also revised by us using the most recent observations.

 

astro-ph/0603510 [abs, ps, pdf, other] :

Title: RHESSI Observation of Chromospheric Evaporation
Authors: Wei Liu, Siming Liu, Yan Wei Jiang, Vahe' Petrosian
Comments: 19 pages, 12 figures (submitted to ApJ)

We present analyses of the spatial and spectral evolution of hard X-ray emission observed by {\it RHESSI} during the impulsive phase of an M1.7 flare on 2003 November 13. In general, as expected, the loop top (LT) source dominates at low energies while the footpoint (FP) sources dominate the high energy emission. At intermediate energies, both the LT and FPs may be seen, but during certain intervals emission from the legs of the loop dominates, in contrast to the commonly observed LT and FP emission. The hard X-ray emission tends to rise above the FPs and eventually merge into a single LT source. This evolution starts first at low energies and proceeds to higher energies. The spectrum of the resultant LT source becomes more and more dominated by a thermal component with an increasing emission measure as the flare proceeds. The soft and hard X-rays show a Neupert-type behavior. With a non-thermal bremsstrahlung model the brightness profile along the loop is used to determine the density profile and its evolution, which reveals a gradual increase of the gas density in the loop. These results are evidence for chromospheric evaporation and are consistent with the qualitative features of hydrodynamic simulations of this phenomenon. However, some observed source morphology and its evolution cannot be accounted for by previous simulations. Therefore simulations with more realistic physical conditions are required to explain the results and the particle acceleration and plasma heating processes.

 

astro-ph/0603511 [abs, ps, pdf, other] :

Title: The Luminosity Function of Nearby Galaxy Clusters II: Redshifts and Luminosity Function for Galaxies in the Region of the Centaurus Cluster
Authors: K. Chiboucas, M. Mateo
Comments: 16 pages, 12 figures, accepted by AJ

We acquired spectra for a random sample of galaxies within a 0.83 square degree region centered on the core of the Centaurus cluster. Radial velocities were obtained for 225 galaxies to limiting magnitudes of V < 19.5. Of the galaxies for which velocities were obtained, we find 35% to be member galaxies. Of the 78 member galaxies, magnitudes range from 11.8 < V < 18.5 (-21.6 < M_{V} < -14.9 for H_o = 70 km s^-1 Mpc^-1) with a limiting central surface brightness of \mu_o < 22.5 mag arcsec^-2. We constructed the cluster galaxy luminosity function by using these spectroscopic results to calculate the expected fraction of cluster members in each magnitude bin. The faint-end slope of the luminosity function using this method is shallower than the one obtained using a statistical method to correct for background galaxy contamination. We also use the spectroscopy results to define surface brightness criteria to establish membership for the full sample. Using these criteria, we find a luminosity function very similar to the one constructed with the statistical background correction. For both, we find a faint-end slope alpha ~ -1.4. Adjusting the surface brightness membership criteria we find that the data are consistent with a faint-end slope as shallow as -1.22 or as steep as -1.50. We describe in this paper some of the limitations of using these methods for constructing the galaxy luminosity function.

 

astro-ph/0603512 [abs, ps, pdf, other] :

Title: Magnetic fields in our Galaxy: How much do we know? III. Progress in the last decade
Authors: J.L. Han (NAOC)
Comments: 8 pages, 4 figures. Invited Talk at "2005 Hanas Pulsar Symposium". To be published in Chinese Journal of Astronomy and Astrophysics

A decade ago, there was very limited knowledge of magnetic fields of our Galaxy. The local fields in the Solar vicinity were known to be directed towards a Galactic longitude $l\sim~90^{\circ}$ with reversed directions at smaller Galacto-radii. The regular field strength was found to be about 2~$\mu$G. The filaments near the Galactic Center show the possible poloidal fields there. There was no information about the magnetic fields in the Galactic halo. In last decade, there has been significant progress on measurements of the Galactic magnetic fields. In the Galactic disk, from the RMs of a large number of newly observed pulsars, large-scale magnetic fields along the spiral arms have been delineated in a much larger region then ever before, with alternating directions in the arm and interarm regions. The toroidal fields in the Galactic halo were revealed to have opposite directions below and above the Galactic plane, which is an indication of A0 dynamo operating in the halo. The strength of large-scale fields also has been found from pulsar RM data to exponentially increase at smaller Galacto-radii. Compared to the steep Kolmogorov spectrum of magnetic energy at small scales, the large-scale magnetic fields show a shallow broken spatial magnetic energy spectrum.

 

astro-ph/0603513 [abs, ps, pdf, other] :

Title: Evidence for a population of beamed radio intermediate quasars
Authors: Tinggui Wang (USTC), Hongyan Zhou (USTC), Junxian Wang (USTC), Youjun Lu (UCB), Yu Lu (USTC)
Comments: 15 pages, 4 figures, 1 table, Accepted to the Astrophysical Journal

Whether radio intermediate quasars possess relativistic jets as radio-loud quasars is an important issue in the understanding of the origin of radio emission in quasars. In this letter, using the two-epoch radio data obtained during Faint Image of Radio Sky at Twenty centimeter sky (FIRST) and NOAO VLA Sky Survey (NVSS), we identify 89 radio variable sources in the Sloan Digital Sky Survey. Among them, more than half are radio intermediate quasars (RL=f2cm/f2500A<250). For all objects with available multiple band radio observations, the radio spectra are either flat or inverted. The brightness temperature inferred from the variability is larger than the synchrotron-self Compton limit for a stationary source in 87 objects, indicating of relativistic beaming. Considering the sample selection and viewing angle effect, we conclude that relativistic jets probably exist in a substantianl fraction of radio intermediate quasars.

 

astro-ph/0603514 [abs, ps, pdf, other] :

Title: The black hole fundamental plane from a uniform sample of radio and X-ray emitting broad line AGNs
Authors: Ran Wang (PKU), Xue-Bing Wu (PKU), Min-Zhi Kong (NAOC)
Comments: 23 pages, 7 figures, ApJ accepted

We derived the black hole fundamental plane relationship among the 1.4GHz radio luminosity (L_r), 0.1-2.4keV X-ray luminosity (L_X), and black hole mass (M) from a uniform broad line SDSS AGN sample including both radio loud and radio quiet X-ray emitting sources. We found in our sample that the fundamental plane relation has a very weak dependence on the black hole mass, and a tight correlation also exists between the Eddington luminosity scaled X-ray and radio luminosities for the radio quiet subsample. Additionally, we noticed that the radio quiet and radio loud AGNs have different power-law slopes in the radio--X-ray non-linear relationship. The radio loud sample displays a slope of 1.39, which seems consistent with the jet dominated X-ray model. However, it may also be partly due to the relativistic beaming effect. For radio quiet sample the slope of the radio--X-ray relationship is about 0.85, which is possibly consistent with the theoretical prediction from the accretion flow dominated X-ray model. We briefly discuss the reason why our derived relationship is different from some previous works and expect the future spectral studies in radio and X-ray bands on individual sources in our sample to confirm our result.

 

astro-ph/0603515 [abs, ps, pdf, other] :

Title: Modeling the gas-phase chemistry of the transitional disk around HD 141569A
Authors: B. Jonkheid, I. Kamp, J.-C. Augereau, E.F. van Dishoeck
Comments: 11 pages, 9 figures. Accepted for publication in A&A

Aims: The chemistry, distribution and mass of the gas in the transitional disk around the 5 Myr old B9.5 V star HD 141569A are constrained.
Methods: A quasi 2-dimensional (2D) chemistry code for photon dominated regions (PDR) is used to calculate the chemistry and gas temperatures in the disk. The calculations are performed for several gas distributions, PAH abundances and values of the total gas mass. The resulting CO J=2-1 and J=3-2 emission lines are computed with a 2D radiative transfer code and are compared to observations.
Results: The CO abundance is very sensitive to the total disk mass because the disk is in a regime where self-shielding just sets in. The observed CO emission lines are best fit by a power-law gas distribution of 80 M_earth starting at 80 AU from the central star, indicating that there is some gas in the inner hole. Predictions are made for intensities of atomic fine-structure lines. [C I], which is the dominant form of carbon in large parts of the disk, is found to be a good alternative tracer of the gas mass.

 

astro-ph/0603516 [abs, ps, pdf, other] :

Title: Models for the Type Ic Hypernova SN 2003lw associated with GRB 031203
Authors: Paolo A. Mazzali, Jinsong Deng, Elena Pian, Daniele Malesani, Nozomu Tominaga, Keiichi Maeda, Ken'ichi Nomoto, Guido Chincarini, Stefano Covino, Massimo Della Valle, Dino Fugazza, Gianpiero Tagliaferri, Avishay Gal-Yam
Comments: 19 pages, 8 figures, accepted for publication in ApJ

The Gamma-Ray Burst 031203 at a redshift z=0.1055 revealed a highly reddened Type Ic Supernova, SN 2003lw, in its afterglow light. This is the third well established case of a link between a long-duration GRB and a type Ic SN. The SN light curve is obtained subtracting the galaxy contribution and is modelled together with two spectra at near-maximum epochs. A red VLT grism 150I spectrum of the SN near peak is used to extend the spectral coverage, and in particular to constrain the uncertain reddening, the most likely value for which is E_{G+H}(B-V) about 1.07 +/- 0.05. Accounting for reddening, SN 2003lw is about 0.3 mag brighter than the prototypical GRB-SN 1998bw. Light curve models yield a 56Ni mass of about 0.55 solar mass. The optimal explosion model is somewhat more massive (ejecta mass about 13 solar mass) and energetic (kinetic energy about 6 times 10^52 erg) than the model for SN 1998bw, implying a massive progenitor (40 - 50 solar mass). The mass at high velocity is not very large (1.4 solar mass above 30000 km/s, but only 0.1 solar mass above 60000 km/s), but is sufficient to cause the observed broad lines. The similarity of SNe 2003lw and 1998bw and the weakness of their related GRBs, GRB031203 and GRB980425, suggest that both GRBs may be normal events viewed slightly off-axis or a weaker but possibly more frequent type of GRB.

 

astro-ph/0603517 [abs, ps, pdf, other] :

Title: Beta decay rates for nuclei with 115 < A < 140 for r-process nucleosynthesis
Authors: Kamales Kar (1), Soumya Chakravarti (2), V.R. Manfredi (3) ((1) Calcutta, India, (2) Pomona, USA, (3) Padova, Italy)
Comments: To be published in Pramana - Journal of Physics (Indian Academy of Sciences). 8 pages LaTeX

For r-process nucleosynthesis the beta decay rates for a number of neutron-rich intermediate heavy nuclei are calculated. The model for the beta strength function is able to reproduce the observed half~lives quite well.

 

astro-ph/0603518 [abs, ps, pdf, other] :

Title: Simulating Cosmic Reionization at Large Scales II: the 21-cm Emission Features and Statistical Signals
Authors: Garrelt Mellema (1,2), Ilian T. Iliev (3), Ue-Li Pen (3), Paul R. Shapiro (4) ((1) ASTRON, (2) Sterrewacht Leiden, (3) CITA, (4) Dept. Astronomy, U. Texas Austin)
Comments: 15 pages, 14 figures, submitted to MNRAS

We present detailed predictions for the redshifted 21cm signal from the epoch of reionization. These predictions are obtained from radiative transfer calculations on the results of large scale (100/h Mpc), high dynamic range, cosmological simulations. We consider several scenarios for the reionization history, of both early and extended reionization. From the simulations we construct and analyze a range of observational characteristics, from the global signal, via detailed images and spectra, to statistical representations of rms fluctuations, angular power spectra, and probability distribution functions to characterize the non-gaussianity of the 21cm signal. (abbreviated abstract)

 

astro-ph/0603519 [abs, ps, pdf, other] :

Title: The GRB060218/SN 2006aj link to Supernova-GRBs blazing and re-brightening by precessing showering Jets
Authors: D.Fargion, M.Grossi
Comments: 9 pages, 8 figures, Submitted for pubblication

A list of puzzles are unanswered by Fireball (even milli-steradiant beamed) explosive GRB and Magnetar spherical one-shoot SGR models. The early GRB 980425 and the last longest GRB060218 are the most emblematic GRBs out of the tune of any Fireball cone models. Too nearby, too soft, too underluminous and too long events. The huge flare of SGR 1806-20 and its radio rebrightening disagree with Magnetar model. Only a persistent, thin (even less than micro steradiant) precessing and spinning gamma jet evolution explains X-gamma time structure and afterglow bumps. The late relic neutron star, X-ray pulsar jet, its spinning and precessing lepton-gamma jet is the candidate blazing sources as anomalous X-ray Pulsars (AXRPs) and Soft Gamma-Ray Repeaters (SGRs). Precessing jet are like SS433 spiral jets. At SN power and in-axis they are GRBs. Late (weeks-months) GRB blazing jets are seldom orphan of their bright SN-OT. The last GRB060218 occurred within its SN2006aj smoothly and soft (because off-axis), ruled by outer jet component and slow by large impact angle. We foresaw OT and radio bumps and re-brightening, in analogy to the third nearest GRB030329-SN2003 event. Late decayed Jets are XRFs or brief GRBs and mostly in galaxy or Local Group distances as SGRs and AXRPs. Electron pairs beams are showering and feeding gamma-X jet by Synchrotron (or Inverse Compton Scattering) far from the dense SN star (or a Neutron Star magnetic fields): energetic and penetrating PeVs muon pairs bundle are the progenitors able to escape the Supernova shells matter and photon opacity decaying far away into PeV electron pairs (and gamma) and neutrinos. The mysterious GRBs (and SGRs) are not the most explosive event of the Universe, but just the most beamed ones.

 

astro-ph/0603520 [abs, ps, pdf, other] :

Title: Vega is a rapidly rotating star
Authors: D. M. Peterson (1), C. A. Hummel (2, 4), T. A. Pauls (3), J. T. Armstrong (3), J. A. Benson (4), G. C. Gilbreath (3), R. B. Hindsley (3), D. J. Hutter (4), K. J. Johnston (4), D. Mozurkewich (5), H. R. Schmitt (3, 6), ((1) Stony Brook, (2) ESO, (3) NRL, (4) USNO, (5) Seabrook Engineering, (6) Interferometrics Inc)
Comments: 10 pages, 2 figures, a Letter to Nature, tentatively scheduled for April 13

Vega, the second brightest star in the northern hemisphere, serves as a primary spectral type standard. While its spectrum is dominated by broad hydrogen lines, the narrower lines of the heavy elements suggested slow to moderate rotation, giving confidence that the ground-based calibration of its visibile spectrum could be safely extrapolated into the ultraviolet and near-infrared (through atmosphere models), where it also serves as the primary photometric calibrator. But there have been problems: the star is too bright compared to its peers and it has unusually shaped absorption line profiles, leading some to suggest that it is a distorted, rapidly rotating star seen pole-on. Here we report optical interferometric observations of Vega which detect the asymmetric brightness distribution of the bright, slightly offset polar axis of a star rotating at 93% of breakup speed. In addition to explaining the unusual brightness and line shape pecularities, this result leads to the prediction of an excess of near-infrared emission compared to the visible, in agreement with observations. The large temperature differences predicted across its surface call into question composition determinations, adding uncertainty to Vega's age and opening the possibility that its debris disk could be substantially older than previously thought.

 

astro-ph/0603521 [abs, ps, pdf, other] :

Title: ChaMP Serendipitous Galaxy Cluster Survey
Authors: W. A. Barkhouse, P. J. Green, A. Vikhlinin, D.-W. Kim, D. Perley, R. Cameron, J. Silverman, A. Mossman, R. Burenin, B. T. Jannuzi, M. Kim, M. G. Smith, R. C. Smith, H. Tananbaum, B. J. Wilkes
Comments: 64 pages, 20 figures, accepted for publication in ApJ

We present a survey of serendipitous extended X-ray sources and optical cluster candidates from the Chandra Multi-wavelength Project (ChaMP). Our main goal is to make an unbiased comparison of X-ray and optical cluster detection methods. In 130 archival Chandra pointings covering 13 square degrees, we use a wavelet decomposition technique to detect 55 extended sources, of which 6 are nearby single galaxies. Our X-ray cluster catalog reaches a typical flux limit of about ~10^-14 erg s^-1 cm^-2, with a median cluster core radius of 21 arcsec. For 56 of the 130 X-ray fields, we use the ChaMP's deep NOAO/4m MOSAIC g, r, and i imaging to independently detect cluster candidates using a Voronoi tessellation and percolation (VTP) method. Red-sequence filtering decreases the galaxy fore/background contamination and provides photometric redshifts to z~0.7. From the overlapping 6.1 square degree X-ray/optical imaging, we find 115 optical clusters (of which 11% are in the X-ray catalog) and 28 X-ray clusters (of which 46% are in the optical VTP catalog). The median redshift of the 13 X-ray/optical clusters is 0.41, and their median X-ray luminosity (0.5-2 keV) is L_X=(2.65\pm0.19)x10^43 ergs s^-1. The clusters in our sample that are only detected in our optical data are poorer on average (~4sigma) than the X-ray/optically matched clusters, which may partially explain the difference in the detection fractions.

 

astro-ph/0603522 [abs, ps, pdf, other] :

Title: Low surface brightness galaxies rotation curves in the low energy limit of $R^n$ gravity : no need for dark matter?
Authors: S. Capozziello, V.F. Cardone, A.- Troisi
Comments: 15, 3 figures

We investigate the possibility that the observed flatness of the rotation curves of spiral galaxies is not an evidence for the existence of dark matter haloes, but rather a signal of the breakdown of General Relativity. To this aim, we consider power - law fourth order theories of gravity obtained by replacing the scalar curvature $R$ with $f(R) = f_0 R^n$ in the gravity Lagrangian. We show that, in the low energy limit, the gravitational potential generated by a pointlike source may be written as $\Phi(r) \propto r^{-1} \left [ 1 + (r/r_c)^{\beta} \right ]$ with $\beta$ a function of the slope $n$ of the gravity Lagrangian and $r_c$ a scalelength depending on the gravitating system properties. In order to apply the model to realistic systems, we compute the modified potential and the rotation curve for spherically symmetric and for thin disk mass distributions. It turns out that the potential is still asymptotically decreasing, but the corrected rotation curve, although not flat, is higher than the Newtonian one thus offering the possibility to fit rotation curves without dark matter. To test the viability of the model, we consider a sample of 15 low surface brightness (LSB) galaxies with combined HI and H$\alpha$ measurements of the rotation curve extending in the putative dark matter dominated region. We find a very good agreement between the theoretical rotation curve and the data using only stellar disk and interstellar gas. Considering the results from the different fits, we find $\beta = 0.58 \pm 0.15$ leading to $1.34 \le n \le 2.41$ as conservative estimate of $n$. The excellent agreement among theoretical and observed rotation curves and the relatively small scatter in $\beta$ makes us confident that $R^n$ gravity may represent a good candidate to solve the dark matter problem.

 

astro-ph/0603523 [abs, ps, pdf, other] :

Title: The dark matter halos of the bluest low surface brightness galaxies
Authors: E. Zackrisson, N. Bergvall, T. Marquart, G. Ostlin
Comments: 14 pages, 9 figures, accepted for publication in Astronomy & Astrophysics

We present BVI photometry and long-slit Halpha rotation curve data obtained with ESO VLT/FORS2 for six low surface brightness galaxies with extremely blue colours and very faint central regions. We find no evidence for a steep central density cusp of the type predicted by many N-body simulations of cold dark matter (CDM) halos. Our observations are instead consistent with dark matter halos characterized by cores of roughly constant density, in agreement with previous investigations. While unremarkable in terms of the central density slope, these galaxies appear very challenging for existing CDM halo models in terms of average central halo density, as measured by the Delta_(V/2) parameter. Since most of our target galaxies are bulgeless disks, our observations also disfavour a recently suggested mechanism for lowering the central mass concentration of the halo by means of a fast collapse phase, as this scenario predicts that the original CDM profile should still be detectable in bulgeless galaxies. Other potential ways of reconciling the CDM predictions with these observations are discussed.

 

astro-ph/0603524 [abs, ps, pdf, other] :

Title: A search for ultra-compact dwarf galaxies in the NGC 1023 group of galaxies
Authors: S. Mieske, M. J. West, C. Mendes de Oliveira
Comments: 5 pages, 4 figures, to appear in the proceedings of ESO Astrophysics Symposia: "Groups of Galaxies in the Nearby Universe", eds. I. Saviane, V. Ivanov, J. Borissova

We present a photometric search for UCD candidates in the nearby galaxy group NGC 1023 (d=11 Mpc) -- the poorest environment searched for UCDs yet --, based on wide field imaging with CFHT. After photometric and morphological selection, we obtain a sample of 21 UCD candidates with -12<M_V<-11 mag, if located at NGC 1023's distance. From spectroscopy taken at Calar Alto observatory, we identify the UCD candidate in closest projection to NGC 1023 as an emission line background galaxy. Our photometric data show that in the NGC 1023 group, the mass spectrum of analogs to Fornax/Virgo UCD is restricted to about 1/4 of the maximum Fornax/Virgo UCD mass. More spectroscopy is needed to further constrain the mass range of UCDs in this galaxy group.

 

astro-ph/0603525 [abs, ps, pdf, other] :

Title: Submillimeter corrections to gravity and the metastability of white dwarf and neutron stars
Authors: Mofazzal Azam, M. Sami
Comments: 5 pages, no figures

The string inspired higher dimensional theories suggest modification of Newton's law at submillimeter length scales. Inter-particle distances in white dwarf and neutron stars are $10^{-10} cms$ and $10^{-13} cms$ respectively, and therefore, the effects of of short distance corrections to gravity deserve investigation. We show, by carrying out explicit analytical many-body calculations that, in the presence of corrections, the normal state of these compact stars become metastable. The actual quantum mechanical ground state of the stars turns out to be unstable. However, the tunneling probability to the unstable ground state is so small that the stars may remain trapped in the metastable state practically for ever.

 

astro-ph/0603526 [abs, ps, pdf, other] :

Title: Bursts from the very early universe
Authors: J. Silk, L. Stodolsky
Comments: eight pages, no figures, typo in metadata corrected

Bursts of weakly interacting particles such as neutrinos or even more weakly interacting particles such as wimps and gravitons from the very early universe would offer a much deeper ``look back time'' to early epochs than is possible with photons.
We consider some of the issues related to the existence of such bursts and their detectability. Characterizing the burst rate by a probability $\cal P$ per Hubble four-volume we find, for events in the radiation-dominated era, that the natural unit of description is the present intensity of the CMB times $\cal P$. The existence of such bursts would make the observation of phenomena associated with very early times in cosmology at least conceptually possible. One might even hope to probe the transplanckian epoch if complexes more weakly interacting than the graviton can exist. Other conceivable applications include the potential detectability of the formation of "pocket" universes'' in a multiverse.

 

astro-ph/0603527 [abs, ps, pdf, other] :

Title: Deep CFHT Photometric Survey of the Entire M33 Galaxy I: Catalogue of 36000 Variable Point Sources
Authors: J.D.Hartman, D.Bersier, K.Z.Stanek, J.-P.Beaulieu, J.Kaluzny, J.-B.Marquette, P.B.Stetson
Comments: Submitted to MNRAS. 20 pages, 16 figures. Catalogue and light curves are available at this http URL animations associated with this paper are available at this http URL a version of the paper with full-resolution images is available at this http URL

We have conducted a variability survey of the local group galaxy M33 using g', r', and i' observations from 27 nights spanning 17 months made with the MegaPrime/MegaCam instrument on the 3.6 m CFHT telescope. We identify more than 36000 variable sources with g',r',i' < 24 out of approximately 2 million point sources in a one square degree field of view. This increases the number of known variables in this galaxy by more than a factor of 20. In this paper we provide a brief description of the data and a general overview of the variable star population which includes more than 800 candidate variable blue and red supergiant stars, more than 2000 Cepheids, and more than 19000 long period variable AGB and RGB stars.

 

astro-ph/0603528 [abs, ps, pdf, other] :

Title: Hubble Space Telescope Identification of the Optical Counterparts of Ultraluminous X-ray Sources in M51
Authors: Yuichi Terashima, Hirohiko Inoue (ISAS/JAXA), Andrew S. Wilson (Univ. of Maryland)
Comments: 10 pages, 5 figures, accepted for publication in ApJ

We present the results of a search for optical identifications of ultraluminous X-ray sources (ULXs) in M51 by using mosaic images taken with the Hubble Space Telescope Advanced Camera for Surveys in filters F435W (B), F555W (V), F814W (I), and F658N (Halpha). Our sample consisting of nine ULXs is defined by analyzing the three Chandra observations of M51 performed in 2000 June, 2001 June, and 2003 Aug. We found four ULXs have one or two candidates for counterparts, while two have multiple stars within their error circles. The other three have no candidate counterparts. Four ULXs are located near or in a star cluster, while others have no association with a cluster. These results indicate that the companion star, environment, and origin of ULXs are probably heterogeneous.

 

astro-ph/0603529 [abs, ps, pdf, other] :

Title: Discovery of VHE gamma-ray emission from 1ES1218+30.4
Authors: MAGIC collaboration: J. Albert, E. Aliu, H. Anderhub, P. Antoranz, A. Armada, M. Asensio, C. Baixeras, J. A. Barrio, M. Bartelt, H. Bartko, D. Bastieri, S. R. Bavikadi, W. Bednarek, K. Berger, C. Bigongiari, A. Biland, E. Bisesi, R. K. Bock, T. Bretz, I. Britvitch, M. Camara, A. Chilingarian, S. Ciprini, J. A. Coarasa, S. Commichau, J. L. Contreras, J. Cortina, V. Curtef, V. Danielyan, F. Dazzi, A. De Angelis, R. de los Reyes, B. De Lotto, E. Domingo-Santamaria, D. Dorner, M. Doro, M. Errando, M. Fagiolini, D. Ferenc, E. Fernandez, R. Firpo, J. Flix, M. V. Fonseca, L. Font, N. Galante, M. Garczarczyk, M. Gaug, M. Giller, F. Goebel, D. Hakobyan, M. Hayashida, T. Hengstebeck, D. Hoehne, J. Hose, P. Jacon, O. Kalekin, D. Kranich, A. Laille, T. Lenisa, P. Liebing, E. Lindfors, et al
Comments: 5 pages, 4 figures, submitted to ApJ

The MAGIC collaboration has studied the high peaked BL-Lac object 1ES1218+30.4 at a redshift z = 0.182, using the MAGIC imaging air Cherenkov telescope located on the Canary island of La Palma. A gamma-ray signal was observed with 6.4sigma significance. The differential energy spectrum for an energy threshold of 120GeV can be fitted by a simple power law yielding F_E(E) = (8.1+-2.1)*10^-7 (E/250GeV)^(-3.0+-0.4) TeV^-1 m^-2 s^-1. During the six days of observation in January 2005 no time variability on time scales of days was found within the statistical errors. The observed integral flux above 350GeV is nearly a factor two below the the upper limit reported by the Whipple Collaboration in 2003.

 

astro-ph/0603530 [abs, ps, pdf, other] :

Title: Gamma-Ray Burst associated Supernovae: Outliers become Mainstream
Authors: E. Pian (1,2), P.A. Mazzali (1,2,3), N. Masetti (4), P. Ferrero (5), et al. ((1) INAF-OATs, Italy, (2) KITP-UCSB, CA, (3) MPA, Germany, (4) INAF-IASF, Bologna, Italy, (5) TLS, Germany)
Comments: Submitted to Nature

During the last eight years a clear connection has been established between the two most powerful explosions in our Universe: core-collapse supernovae (SNe) and long gamma ray bursts (GRBs). Theory suggests that every GRB is simultaneously accompanied by a SN, but in only a few nearby cases have these two phenomena been observed together. We report the discovery and daily monitoring of SN2006aj associated with the GRB060218. Because the event was the second closest GRB, both explosions could be examined in detail. GRB060218 had an unusually soft spectrum, long duration, and a total energy 100 to 1000 times less than most other GRBs. Yet SN2006aj was similar to those in other GRBs, aside from rising more rapidly and being ~40% fainter. Taken together, these observations suggest that GRBs have two components: a broad, energetic, but only mildly relativistic outflow that makes a SN, and a more narrowly focused, highly relativistic jet responsible for the GRB. The properties of the GRB jet apparently vary greatly from event to event, while the broad SN outflow varies much less. Low energy transients like GRB060218 may be the most common events in the Universe.

 

astro-ph/0603531 [abs, ps, pdf, other] :

Title: Magnetic Field Structure from Synchrotron Polarization
Authors: Rainer Beck (MPI fuer Radioastronomie, Bonn, Germany)
Comments: 18 pages, 9 figures. To be published in "Polarisation 2005" (Proc. of the conference held in Paris, 12-15 Sept. 2005), eds. F. Boulanger and M.A. Miville-Deschenes, EAS Publications Series

Total magnetic fields in spiral galaxies, as observed through their total synchrotron emission, are strongest (up to \simeq 30\mu G) in the spiral arms. The degree of radio polarization is low; the field in the arms must be mostly turbulent or tangled. Polarized synchrotron emission shows that the resolved regular fields are generally strongest in the interarm regions (up to \simeq 15\mu G), sometimes forming 'magnetic arms' parallel to the optical arms. The field structure is spiral in almost every galaxy, even in flocculent and bright irregular types which lack spiral arms. The observed large-scale patterns of Faraday rotation in several massive spiral galaxies reveal coherent regular fields, as predicted by dynamo models. However, in most galaxies observed so far no simple patterns of Faraday rotation could be found. Either many dynamo modes are superimposed and cannot be resolved by present-day telescopes, or most of the apparently regular field is in fact anisotropic random, with frequent reversals, due to shearing and compressing gas flows. In galaxies with massive bars, the polarization pattern follows the gas flow. However, around strong shocks in bars, the compression of the regular field is much lower than that of the gas; the regular field decouples from the cold gas and is strong enough to affect the flow of the diffuse warm gas. -- The average strength of the total magnetic field in the Milky Way is 6\mu G near the sun and increases to 20-40\mu G in the Galactic center region. The Galactic field is mostly parallel to the plane, except in the center region. Rotation measure data from pulsars indicate several field reversals, unlike external galaxies, but some reversals could be due to distortions of the nearby field.

 

astro-ph/0603532 [abs, pdf] :

Title: The Eclipsing ULX in NGC 3379
Authors: G. Fabbiano, D.-W. Kim, T. Fragos, V. Kalogera, A. R. King, L. Angelini, R. L. Davies, J. S. Gallagher, S. Pellegrini, G. Trinchieri, S. E. Zepf, A. Zezas
Comments: Submitted to ApJ, 16 pages, 3 color figures

We report recent Chandra observations of the ULX in the elliptical galaxy NGC3379 that clearly detect two flux variability cycles. Comparing these data with the Chandra observation of ~5yr ago, we measure a flux modulation with a period of ~12.6hr. Moreover, we find that the emission undergoes a correlated spectral modulation, becoming softer at low flux. We argue that our results establish this source as a ULX binary in NGC3379. Given the old stellar population of this galaxy, the ULX is likely to be a soft transient, however historical X-ray sampling suggests that the current on phase has lasted ~10yr. We discuss our results in terms of ADC and wind-feedback models. We constrain the donor mass and orbital period at the onset of mass transfer within 1.15-1.4M and 12.5-16hr, respectively. The duration of the mass-transfer phase so far is probably ~1Gyr and the binary has been a soft X-ray transient throughout this time. These constraints are insensitive to the mass of the accretor.

 

astro-ph/0603533 [abs, ps, pdf, other] :

Title: High resolution HI and radio continuum observations of the SNR G290.1-0.8
Authors: Estela M. Reynoso, Simon Johnston, Anne J. Green, Baerbel S. Koribalski
Comments: Accepted in Monthly Notices of the Royal Astronomical Society

We have observed the supernova remnant (SNR) G290.1-0.8 in the 21-cm HI line and the 20-cm radio continuum using the Australia Telescope Compact Array (ATCA). The HI data were combined with data from the Southern Galactic Plane Survey to recover the shortest spatial frequencies. In contrast, HI absorption was analyzed by filtering extended HI emission, with spatial frequencies shorter than 1.1 k-lambda. The low-resolution ATCA radio continuum image of the remnant shows considerable internal structure, resembling a network of filaments across its 13 arcmin diameter. A high-resolution ATCA radio continuum image was also constructed to study the small scale structure in the SNR. It shows that there are no structures smaller than ~17", except perhaps for a bright knot to the south, which is probably an unrelated object. The HI absorption study shows that the gas distribution and kinematics in front of SNR G290.1-0.8 are complex. We estimate that the SNR probably lies in the Carina arm, at a distance 7 (+/- 1) kpc. In addition, we have studied nearby sources in the observed field using archival multiwavelength data to determine their characteristics.

 

astro-ph/0603534 [abs, ps, pdf, other] :

Title: Higher order contributions to the primordial non-gaussianity
Authors: Ignacio Zaballa, Yeinzon Rodriguez, David H. Lyth
Comments: 6 pages. 2 figures

In this paper we calculate additional contributions to that part of the non-Gaussianity of the curvature perturbation, which come from the three-point correlator of the field perturbations. We estimate this contribution in the following models for its origin: single-component inflation, multi-component chaotic inflation, a two-component "hybrid" inflationary model, and the curvaton scenario. In all of these models, the additional contributions to the primordial non-gaussianity considered here, are too small to be ever detected.

 

astro-ph/0603535 [abs, ps, pdf, other] :

Title: Towards a Cosmological Hubble Diagram for Type II-P Supernovae
Authors: Peter Nugent (1), Mark Sullivan (2), Richard Ellis (3), Avishay Gal-Yam (3 and 4), Douglas C. Leonard (3 and 5), D. Andrew Howell (2), Pierre Astier (6), Raymond G. Carlberg (2), Alex Conley (2), Sebastien Fabbro (7), Dominique Fouchez (8), James D. Neill (9), Reynald Pain (6), Kathy Perrett (2), Chris J. Pritchet (9), Nicolas Regnault (6) ((1) Lawrence Berkeley National Laboratory, (2) University of Toronto, (3) California Institute of Technology, (4) Hubble Postdoctoral Fellow, (5) NSF Astronomy and Astrophysics Postdoctoral Fellow, (6) LPNHE, CNRS-IN2P3 and University of Paris VI & VII, (7) CENTRA, (8) CPPM, CNRS-IN2P3 and University Aix Marseille II, (9) University of Victoria)
Comments: 36 pages, 16 figures, accepted for publication in ApJ

We present the first high-redshift Hubble diagram for Type II-P supernovae (SNe II-P) based upon five events at redshift up to z~0.3. This diagram was constructed using photometry from the Canada-France-Hawaii Telescope Supernova Legacy Survey and absorption line spectroscopy from the Keck observatory. The method used to measure distances to these supernovae is based on recent work by Hamuy & Pinto (2002) and exploits a correlation between the absolute brightness of SNe II-P and the expansion velocities derived from the minimum of the Fe II 516.9 nm P-Cygni feature observed during the plateau phases. We present three refinements to this method which significantly improve the practicality of measuring the distances of SNe II-P at cosmologically interesting redshifts. These are an extinction correction measurement based on the V-I colors at day 50, a cross-correlation measurement for the expansion velocity and the ability to extrapolate such velocities accurately over almost the entire plateau phase. We apply this revised method to our dataset of high-redshift SNe II-P and find that the resulting Hubble diagram has a scatter of only 0.26 magnitudes, thus demonstrating the feasibility of measuring the expansion history, with present facilities, using a method independent of that based upon supernovae of Type Ia.

 

astro-ph/0603536 [abs, ps, pdf, other] :

Title: Microlensing modulation by binaries
Authors: Florian Dubath, Maria Alice Gasparini, Ruth Durrer

We compute the effect of the lens quadrupole on microlensing. The time dependence of the quadrupole can lead to specific modulations of the amplification signal. We study especially binary system lenses in our galaxy. The modulation is observable if the rotation period of the system is smaller than the time over which the amplification is significant and if the impact parameter of the passing light ray is sufficiently close to the Einstein radius so that the amplification is very large. Observations of this modulation can reveal important information on the quadrupole and thus on the gravitational radiation emitted by the lens.

 

astro-ph/0603537 [abs, ps, pdf, other] :

Title: The differing locations of massive stellar explosions
Authors: A. S. Fruchter, A. J. Levan, L. Strolger, P. M. Vreeswijk, S. E. Thorsett, D. Bersier, I. Burud, J. M. Castro Ceró, n A. Castro-Tirado, C. Conselice, T. Dahlen, H. C. Ferguson, J. P. U. Fynbo, P. M. Garnavich, R. A. Gibbons, J. Gorosabel, T. R. Gull, J. Hjorth, S. T. Holland, C. Kouveliotou, Z. Levay, M. Livio, M. R. Metzger, P. E. Nugent, L. Petro, E. Pian, J. E. Rhoads, A. G. Riess, K. C. Sahu, A. Smette, N. R. Tanvir, R. A. M. J. Wijers, S. E. Woosley
Comments: 27 pages, 4 figures, submitted to Nature on 22 August 2005, revised 9 February 2006. Supplementary material referred to in the text can be found at this http URL

When massive stars exhaust their fuel they collapse and often produce the extraordinarily bright explosions known as core-collapse supernovae. On occasion, this stellar collapse also powers an even more brilliant relativistic explosion known as a long-duration gamma-ray burst. One would then expect that gamma-ray bursts and supernovae should be found in similar environments. Here we show that this expectation is wrong. Using Hubble Space Telescope imaging of the host galaxies of long-duration gamma-ray bursts and core-collapse supernovae, we find that the gamma-ray bursts are far more concentrated on the very brightest regions of their hosts than are the supernovae. Furthermore, the host galaxies of the gamma-ray bursts are significantly fainter and more irregular than the hosts of the supernovae. Together these results suggest that long-duration gamma-ray bursts are associated with the very most massive stars and may be restricted to galaxies of limited chemical evolution. Our results directly imply that long-duration gamma-ray bursts are relatively rare in galaxies such as our own Milky Way.

 

astro-ph/0603538 [abs, ps, pdf, other] :

Title: Testing and selection cosmological models with dark energy
Authors: Marek Szydlowski, Aleksandra Kurek
Comments: Talk at Albert Einstein Century International Conference at Palais de l'Unesco, Paris, France, 18-23 July 2005; to appear in the Proceedings; AIP style files included, 6 pages, 2 figures

It is described dynamics of a large class of accelerating cosmological models in terms of dynamical systems of the Newtonian type. The evolution of the models is reduced to the motion of a particle in a potential well parameterized by the scale factor. This potential function can be reconstructed from distant supernovae type Ia data and many cosmological models represented in terms of the potential becomes in a good agreement with current observational data. It is proposed to use the information criteria to overcome this degeneracy within a class of A) dark energy models and B) simple models basing on modification of the FRW equation. Two class of models can be recommended by the Akaike (AIC) and Schwarz (BIC) information criteria: the phantom and $\Lambda$CDM models.

 

astro-ph/0603539 [abs, ps, pdf, other] :

Title: Inflation models after WMAP year three
Authors: Laila Alabidi, David H. Lyth
Comments: 4 pages

The survey of models in astro-ph/0510441 is updated. For the first time, a large fraction of the models are ruled out at more than $3\sigma$.

 

astro-ph/0603540 [abs, ps, pdf, other] :

Title: Challenges in Detecting Gamma-Rays From Dark Matter Annihilations in the Galactic Center
Authors: Gabrijela Zaharijas, Dan Hooper
Comments: 8 pages, 10 figures

Atmospheric Cerenkov Telescopes, including HESS and MAGIC, have detected a spectrum of gamma-rays from the galactic center region which extends from $\sim$200 GeV or lower, to at least $\sim$10 TeV. Although the source of this radiation is not yet known, the spectrum appears to behave as a simple power-law, which is not the expectation for gamma-rays generated through the annihilation of dark matter particles. If instead we conclude that the source of these gamma-rays is astrophysical in origin, this spectrum will constitute a background for future dark matter searches using gamma-rays from this region. In this paper we study how this background will affect the prospects for experiments such as GLAST to detect dark matter in the galactic center. We find that only a narrow range of dark matter annihilation rates are potentially observable by GLAST given this newly discovered background and considering current constraints from EGRET and HESS. We also find that a detection of line emission, while not completely ruled out, is only possible for a very narrow range of dark matter models and halo profiles.