Title: The Importance of Off-Jet Relativistic Kinematics in Gamma-Ray Burst Jet
Models Authors:T. Q. Donaghy Comments: 12 pages, 13 figures. Ph.D. dissertation, submitted to ApJ
Gamma-Ray Bursts (GRBs) are widely thought to originate from collimated jets
of material moving at relativistic velocities. Emission from such a jet should
be visible even when viewed from outside the angle of collimation. I summarize
recent work on the special relativistic transformation of the burst quantities
Eiso and Epeak as a function of viewing angle, where Eiso is the
isotropic-equivalent energy of the burst and Epeak is the peak of the burst
spectrum in the power nu F_nu. The formulae resulting from this work serve as
input for a Monte Carlo population synthesis method, with which I investigate
the importance of off-jet relativistic kinematics as an explanation for a class
of GRBs termed "X-ray Flashes" (XRFs). I do this in the context of several
top-hat shaped variable opening-angle jet models. I find that such models
predict a large population of off-jet bursts that are observable and that lie
away from the Epeak ~ Eiso^(1/2) relation. The predicted burst populations are
not seen in current datasets. I investigate the effect of the bulk gamma value
upon the properties of this population of off-jet bursts, as well as the effect
of including an Omega0-Egamma correlation to jointly fit the Epeak ~ Eiso^(1/2)
and Epeak ~ Egamma^(beta) relations, where Omega0 is the opening solid angle of
the GRB jet. I find that the XRFs seen by HETE-2 and BeppoSAX cannot be easily
explained as classical GRBs viewed off-jet. I also find that an inverse
correlation between gamma and Omega0 has the effect of greatly reducing the
visibility of off-jet events. Therefore, unless gamma > 300 for all bursts or
unless there is a strong inverse correlation between gamma and Omega0, top-hat
variable opening-angle jet models produce a significant population of bursts
away from the Epeak ~ Eiso^(1/2) and Epeak ~ Egamma^(beta) relations.
We use the OGLE-II and OGLE-III data in conjunction with the 2MASS
near-infrared (NIR) photometry to identify and study Miras and Semiregular
Variables (SRV) in the Large Magellanic Cloud. We found in total 3221 variables
of both types, populating two of the series of NIR period--luminosity (PL)
sequences. The majority of these objects are double periodic pulsators, with
periods belonging to both PL ridges. We indicate that in the period - Wesenheit
index plane the oxygen-rich and carbon-rich AGB stars from the NIR PL sequences
C, C' and D split into well separated ridges. Thus, we discover an effective
method of distinguishing between O-rich and C-rich Miras, SRV and stars with
Long Secondary Periods using their V and I band photometry. We present an
empirical method of estimating the mean K_s magnitudes of the Long Period
Variables using single-epoch K_s measurements and complete light curves in the
I band. We utilize these corrected magnitudes to show that the O-rich and
C-rich Miras and SRV follow somewhat different K_s band PL relations.
Title: Are GRB shocks mediated by the Weibel instability? Authors:Yuri Lyubarsky,
David Eichler Comments: 13 pages, 3 figures
It is estimated that the Weibel instability is not generally an effective
mechanism for generating ultrarelativistic astrophysical shocks. Even if the
upstream magnetic field is as low as in the interstellar medium, the shock is
mediated not by the Weibel instability but by the Larmor rotation of protons in
the background magnetic field. Future simulations should be able to verify or
falsify our conclusion.
Title: The Convective Urca Process with Implicit Two-Dimensional Hydrodynamics Authors:Josef Stein,
J.Craig Wheeler Comments: 22 pages, 11 figures, accepted for publication in the Astrophysical
Journal
Consideration of the role of the convective flux in the thermodymics of the
convective Urca neutrino loss process in degenerate, convective, quasi-static,
carbon-burning cores shows that the convective Urca process slows down the
convective current around the Urca-shell, but, unlike the "thermal" Urca
process, does not reduce the entropy or temperature for a given convective
volume. Here we demonstrate these effects with two-dimensional numerical
hydrodynamical calculations. These two-dimensional implicit hydrodynamics
calculations invoke an artificial speeding up of the nuclear and weak rates.
They should thus be regarded as indicative, but still qualitative. We find
that, compared to a case with no Urca-active nuclei, the case with Urca effects
leads to a higher entropy in the convective core because the energy released by
nuclear burning is confined to a smaller volume by the effective boundary at
the Urca shell. All else being equal, this will tend to accelerate the
progression to dynamical runaway. We discuss the open issues regarding the
impact of the convective Urca process on the evolution to the "smoldering
phase" and then to dynamical runaway.
We estimate the polarized thermal dust emission from MHD simulations of
protostellar collapse and outflow formation in order to investigate alignment
of outflows with magnetic fields. The polarization maps indicate that alignment
of an outflow with the magnetic field depends on the field strength inside the
cloud core; the direction of the outflow, projected on the plane of the sky, is
aligned preferentially with the mean polarization vector for a cloud core with
a magnetic field strength of 80 microgauss, while it does not tend to be
aligned for 50 microgauss as long as the 1000 AU scale is considered. The
direction of the magnetic field at the cloud center is probed by the direction
of the outflow. In addition, the magnetic field at the cloud center can be
revealed by ALMA even when the source is embedded deeply in the envelope. The
Chandrasekhar-Fermi formula is examined using the polarization maps, indicating
that the field strength predicted by the formula should be corrected by a
factor of 0.24 - 0.44. The correction factor has a tendency to be lower for a
cloud core with a weaker magnetic field.
Title: Effect of Reconnection Probability on Cosmic (Super)string Network
Density Authors:A. Avgoustidis,
E. P. S. Shellard Comments: 6 pages, 4 figures
We perform numerical simulations of cosmic string evolution with
intercommuting probability $P$ in the range $5\times 10^{-3}\le P\le 1$, both
in the matter and radiation eras, using a modified version of the
Allen-Shellard code. We find that the dependence of the scaling density on $P$
is significantly different than the suggested $\rho\propto P^{-1}$ form. In
particular, for probabilities greater than $P\simeq 0.1$, $\rho(1/P)$ is
approximately flat, but for $P$ less than this value it is well-fitted by a
power-law with exponent $0.6^{+0.15}_{-0.12}$. This shows that the enhancement
of string densities due to a small intercommuting probability is much less
prominent than initially anticipated. We interpret the flat part of $\rho(1/P)$
in terms of multiple opportunities for string reconnections during one crossing
time, due to small-scale wiggles. We also propose a two-scale model
incorporating the key physical mechanisms, which satisfactorily fits our
results over the whole range of $P$ covered by the simulations.
We present Spitzer Space Telescope observations of the z=2.38 lya-emitter
over-density associated with galaxy cluster J2143-4423, the largest known
structure (110 Mpc) above z=2. We imaged 22 of the 37 known lya-emitters within
the filament-like structure, using the MIPS 24um band. We detected 6 of the
lya-emitters, including 3 of the 4 clouds of extended (>50 kpc) lyman alpha
emission, also known as Lya Blobs. Conversion from rest-wavelength 7um to total
far-infrared luminosity using locally derived correlations suggests all the
detected sources are in the class of ULIRGs, with some reaching Hyper-LIRG
energies. Lya blobs frequently show evidence for interaction, either in HST
imaging, or the proximity of multiple MIPS sources within the Lya cloud. This
connection suggests that interaction or even mergers may be related to the
production of Lya blobs. A connection to mergers does not in itself help
explain the origin of the Lya blobs, as most of the suggested mechanisms for
creating Lya blobs (starbursts, AGN, cooling flows) could also be associated
with galaxy interactions.
Title: The Ups and Downs of the Hubble Constant Authors:G.A. Tammann (Astr. Inst. Univ. Basel) Comments: 30 pages, 12 figures, 2 tables. 79th Annual Scientific Meeting of the
Astronomische Gesellschaft 2005, Karl-Schwarzschild-Lecture, to appear in
Reviews in Modern Astronomy, 19, 1
A brief history of the determination of the Hubble constant H_0 is given.
Early attempts following Lemaitre (1927) gave much too high values due to
errors of the magnitude scale, Malmquist bias and calibration problems. By 1962
most authors agreed that 75< H_0 <130. After 1975 a dichotomy arose with values
near 100 and others around 55. The former came from apparent-magnitude-limited
samples and were affected by Malmquist bias. New distance indicators were
introduced; they were sometimes claimed to yield high values of H_0, but the
most recent data lead to H_0 in the 60's, yet with remaining difficulties as to
the zero-point of the respective distance indicators. SNe Ia with their large
range and very small luminosity dispersion (avoiding Malmquist bias) offer a
unique opportunity to determine the large-scale value of H_0. Their maximum
luminosity can be well calibrated from 10 SNe Ia in local parent galaxies whose
Cepheids have been observed with HST. An unforeseen difficulty - affecting all
Cepheid distances - is that their P-L relation varies from galaxy to galaxy,
presumably in function of metallicity. A proposed solution is summarized here.
The conclusion is that H_0 = 63.2 +/- 1.3 (random) +/- 5.3 (systematic) on all
scales. The expansion age becomes then (with Omega_m=0.3, Omega_Lambda=0.7)
15.1 Gyr.
Title: Birth and Evolution of Isolated Radio Pulsars Authors:C.-A. Faucher-Giguere (1, 2),
V. M. Kaspi (1) ((1) McGill University, (2) Harvard-Smithsonian Center for Astrophysics) Comments: 73 preprint pages, including 8 tables and 15 figures. ApJ submission
revised following the referee's comments
We investigate the birth and evolution of Galactic isolated radio pulsars. We
begin by estimating their birth space velocity distribution from proper motion
measurements of Brisken et al. (2002, 2003). We find no evidence for
multimodality of the distribution and favor one in which the absolute
one-dimensional velocity components are exponentially distributed and with a
three-dimensional mean velocity of 380^{+40}_{-60} km s^-1. We then proceed
with a Monte Carlo-based population synthesis, modelling the birth properties
of the pulsars, their time evolution, and their detection in the Parkes and
Swinburne Multibeam surveys. We present a population model that appears
generally consistent with the observations. Our results suggest that pulsars
are born in the spiral arms, with a Galactocentric radial distribution that is
well described by the functional form proposed by Yusifov & Kucuk (2004), in
which the pulsar surface density peaks at radius ~3 kpc. The birth spin period
distribution extends to several hundred milliseconds, with no evidence of
multimodality. Models which assume the radio luminosities of pulsars to be
independent of the spin periods and period derivatives are inadequate, as they
lead to the detection of too many old simulated pulsars in our simulations.
Dithered radio luminosities proportional to the square root of the spin-down
luminosity accommodate the observations well and provide a natural mechanism
for the pulsars to dim uniformly as they approach the death line, avoiding an
observed pile-up on the latter. There is no evidence for significant torque
decay (due to magnetic field decay or otherwise) over the lifetime of the
pulsars as radio sources (~100 Myr). Finally, we estimate the pulsar birthrate
and total number of pulsars in the Galaxy.
Title: What Do We Really Know About Cosmic Acceleration? Authors:Charles Shapiro (1,2),
Michael S. Turner (1,2) ((1) University of Chicago, (2) Kavli Institute for Cosmological Physics) Comments: 9 pages, 8 figures
Essentially all of our knowledge of the acceleration history of the Universe
- including the acceleration itself - is predicated upon the validity of
general relativity. Without recourse to this assumption, we use SNeIa to
analyze the expansion history and find (i) very strong (5 sigma) evidence for a
period of acceleration, (ii) strong evidence that the acceleration has not been
constant, (iii) evidence for an earlier period of deceleration and (iv) only
weak evidence that the Universe has not been decelerating since z~0.3.
Title: Local virial relation and velocity anisotropy in self-gravitating system Authors:Y. Sota,
O. Iguchi,
M. Morikawa,
A. Nakamichi Comments: Proceedings of The Third 21COE Symposium : Astrophysics as
Interdisciplinary Science
We investigate the merging process in N-body self-gravitating system from the
viewpoints of the local virial relation which is the relation between the local
kinetic energy and the local potential. We compare both the density profile and
the phase space density profile in cosmological simulations with the critical
solutions of collisionless static state satisfying the local virial (LV)
relation. We got the results that the critical solution can explain the
characteristic density profile with the appropriate value of anisotropy
parameter $\beta \sim 0.5$. It can also explain the power law of the phase
space density profile in the outer part of a bound state. However, it fails in
explaining the central low temperature part which is connected to the scale
invariant phase space density. It can be well fitted to the critical solution
with the higher value of$\beta \sim 0.75$. These results indicate that the LV
relation is not compatible with the scale invariant phase space density in
cosmological simulation.
Title: The Molonglo Southern 4 Jy sample (MS4). I. Definition Authors:A. M. Burgess,
R. W. Hunstead Comments: 59 pages, 5 Postscript figures. To appear in Astronomical Journal.
For a higher-resolution version of Figure 2, see
this http URL
We have defined a complete sample of 228 southern radio sources at 408 MHz
with integrated flux densities S_408 > 4.0 Jy, Galactic latitude |b| > 10 deg
and declination -85 deg < delta < -30 deg. The main finding survey used was the
Molonglo Reference Catalogue. We describe in detail how the Molonglo Southern 4
Jy sample (MS4) was assembled and its completeness assessed. Sources in the
sample were imaged at 843 MHz with the Molonglo Observatory Synthesis Telescope
to obtain positions accurate to about 1 arcsec, as well as flux densities and
angular sizes; follow-up radio and optical observations are presented in Paper
II. Radio spectra for the MS4 have been compiled from the literature and used
to estimate flux densities at 178 MHz. The strong-source subset of MS4, with
S_178 > 10.9 Jy (SMS4), provides a southern sample closely equivalent to the
well-studied northern 3CRR sample. Comparison of SMS4 with 3CRR shows a
reassuring similarity in source density and median flux density between the two
samples.
We present the initial results of a 3-mm spectral line survey towards 83
methanol maser selected massive star-forming regions. Here we report
observations of the J=5-4 and 6-5 rotational transitions of methyl cyanide
(CH3CN) and the J=1-0 transition of HCO+and H13CO+.
CH3CN emission is detected in 58 sources (70 %) of our sample). We estimate
the temperature and column density for 37 of these using the rotational diagram
method. The temperatures we derive range from 28-166 K, and are lower than
previously reported temperatures, derived from higher J transitions. We find
that CH3CN is brighter and more commonly detected towards ultra-compact HII
(UCHII) regions than towards isolated maser sources. Detection of CH3CN towards
isolated maser sources strongly suggests that these objects are internally
heated and that CH3CN is excited prior to the UCHII phase of massive
star-formation.
HCO+ is detected towards 82 sources (99 % of our sample), many of which
exhibit asymmetric line profiles compared to H13CO+. Skewed profiles are
indicative of inward or outward motions, however, we find approximately equal
numbers of red and blue-skewed profiles among all classes. Column densities are
derived from an analysis of the HCO+ and H13CO+ line profiles.
80 sources have mid-infrared counterparts: 68 seen in emission and 12 seen in
absorption as `dark clouds'. Seven of the twelve dark clouds exhibit asymmetric
HCO+ profiles, six of which are skewed to the blue, indicating infalling
motions. CH3CN is also common in dark clouds, where it has a 90 % detection
rate.
Title: The Molonglo Southern 4 Jy sample (MS4). II. ATCA imaging and optical
identification Authors:A. M. Burgess,
R. W. Hunstead Comments: 102 pages; 6 figures in 21 Postscript files. To appear in
Astronomical Journal. For higher-resolution versions of some figures, see
this http URL
Of the 228 sources in the Molonglo Southern 4 Jy Sample (MS4), the 133 with
angular sizes < 35 arcsec have been imaged at 5 GHz at 2-4 arcsec resolution
with the Australia Telescope Compact Array. More than 90% of the sample has
been reliably optically identified, either on the plates of the UK Schmidt
Southern Sky Survey or on R-band CCD images made with the Anglo-Australian
Telescope. A subsample of 137 sources, the SMS4, defined to be a close southern
equivalent of the northern 3CRR sample, was found to have global properties
mostly consistent with the northern sample. Linear sizes of MS4 galaxies and
quasars were found to be consistent with galaxy-quasar unification models of
orientation and evolution.
Title: ROSAT observations of the soft X-ray background and of the cluster soft
excess emission in the Hercules supercluster Authors:Max Bonamente,
Richard Lieu,
Jelle Kaastra Comments: 17 pages, published in A. & A Journal-ref: Published in A. & A., vol. 443, p. 29 (2005)
Recent observations with the XMM-Newton satellite confirmed the existence of
the soft excess phenomenon in galaxy clusters, earlier discovered in several
EUVE, ROSAT and BeppoSAX observations. Among the clusters for which XMM has
reported detection of soft excess emission are MKW03s and A2052, two clusters
in the Hercules concentration.
The Hercules supercluster lies along the southern extension of the North
Polar Spur, a region of bright soft X-ray emission clearly visible in ROSAT
All-Sky Survey images. We analyze 11 pointed ROSAT PSPC observations toward 3
clusters in the Hercule concentration, MKW03s, A2052 and A2063, and 8
neighboring fields in order to investigate the soft X-ray emission in that
region of the sky. We find that the soft X-ray emission varies by a factor of
few on scales of few degrees, rendering the background subtraction a complex
task. If the Noth Polar Spur emission is of local origin, we find that only
A2052 and A2063 have evidence of cluster soft excess emission, and that the
OVII emission lines detected in XMM observations of A2052 and MKW03s are not
associated with the cluster. If part or all of the North Polar Spur soft X-ray
enhancement is of extragalactic nature, the three clusters feature strong soft
excess emission, and the OVII emission lines observed by XMM are genuinely
associated with the clusters.
We interpret the soft excess emission with the presence of warm gas, either
intermixed with the hot intra-cluster medium or in filamentary structures
located around the clusters, and estimate that the warm gas is approximately as
massive as the hot intra-cluster medium.
Nonlinear behaviour of galactic dynamos is studied, allowing for magnetic
helicity removal by the galactic fountain flow. A suitable advection speed is
estimated, and a one-dimensional mean-field dynamo model with dynamic
alpha-effect is explored. It is shown that the galactic fountain flow is
efficient in removing magnetic helicity from galactic discs. This alleviates
the constraint on the galactic mean-field dynamo resulting from magnetic
helicity conservation and thereby allows the mean magnetic field to saturate at
a strength comparable to equipartition with the turbulent kinetic energy.
Title: A High-Accuracy Method for the Removal of Point Sources from Maps of the
Cosmic Microwave Background Authors:Anisa T. Bajkova Comments: 13 pages, 7 figures Journal-ref: Astronomy Reports, Vol.49, N 12, 2005, pp.947-957
A new method for removing point radio sources and other non-Gaussian noise is
proposed as a means of improving the accuracy of estimates of the angular power
spectrum of the cosmic microwave background (CMB). The main idea of the method
is to reconstruct fluctuations of the CMB in places contaminated by such
emission, while traditional methods simply exclude these regions from
consideration, leading to the appearance of "holes" in the resulting maps. The
fundamental possibility of reconstructing the CMB signal in such holes follows
from the analytical properties of a function with a finite spatial spectrum
(the Silk damping frequency). A two-dimensional median filter is used to
localize the point radio sources. Results of simulations of the method for maps
of modest size are presented. The efficiency of applying the method to
reconstruct the CMB from data with limited resolution and contaminated by
appreciable pixel noise is investigated. The fundamental possibility of
applying the method to reconstruct the CMB distribution in the region of the
Galaxy is also demonstrated.
Title: 3D spectroscopy as a tool for investigation of the BLR of lensed QSOs Authors:L. C. Popovic (AOB) Comments: ESO Astrophysics Symposia "Science Perspectives for 3D Spectroscopy"
(eds, M. Kissler-Patig, M.M. Roth and J.R. Walsh), Garching, Germany, 10-14
October 2005
Selective amplification of the line and continuum source by microlensing in a
lensed quasar can lead to changes of continuum spectral slopes and line shapes
in the spectra of the quasar components. Comparing the spectra of different
components of the lensed quasar and the spectra of an image observed in
different epochs one can infer the presence of millilensing, microlensing and
intrinsic variability. Especially, microlensing can be used for investigation
of the unresolved broad line (BLR) and continuum emitting region structure in
active galactic nuclei (AGN). Therefore the spectroscopic monitoring of
selected lensed quasars with 3D spectroscopy open new possibility for
investigation of the BLR structure in AGN. Here we discuss observational
effects that may be present during the BLR microlensing in the spectra of
lensed QSOs.
Title: A Precessing Ring Model for Low-Frequency Quasi-periodic Oscillations Authors:Jeremy D. Schnittman (U Maryland),
Jeroen Homan (MIT),
Jon M. Miller (U Michigan) Comments: Accepted to ApJ, 22 pages, 7 figures
We develop a simple physical model to describe the most common type of
low-frequency quasi-periodic oscillations (QPOs) seen in a number of accreting
black hole systems, as well as the shape of the relativistically broadened iron
emission lines that often appear simultaneously in such sources. The model is
based on an inclined ring of hot gas that orbits the black hole along geodesic
trajectories. For spinning black holes, this ring will precess around the spin
axis of the black hole at the Lense-Thirring (``frame-dragging'') frequency.
Using a relativistic ray-tracing code, we calculate X-ray light curves and
observed energy spectra as a function of the radius and tilt angle of the ring,
the spin magnitude, and the inclination of the black hole. The model predicts
higher-amplitude QPOs for systems with high inclinations, as seen in a growing
number of black hole binary systems. We find that the Rossi X-ray Timing
Explorer observations of low-frequency QPOs in GRS 1915+105 are consistent with
a ring of radius R ~ 10M orbiting a black hole with spin a/M ~0.5 and
inclination angle of i ~ 70 deg. Finally, we describe how future X-ray missions
may be able to use simultaneous timing and spectroscopic observations to
measure the black hole spin and probe the inner-most regions of the accretion
disk.
Title: Molecular dynamics study of photodissociation of water in crystalline
and amorphous ice Authors:Stefan Andersson,
Ayman Al-Halabi,
Geert-Jan Kroes,
Ewine F. van Dishoeck Comments: 71 pages and 17 figures, consisting of paper (54 pages and 11
figures) and supporting material (17 pages and 6 figures). To be published in
J. Chem. Phys. (2006)
We present results of classical dynamics calculations, performed to study the
photodissociation of water in crystalline and amorphous ice surfaces at a
surface temperature of 10 K. Dissociation in the top six monolayers is
considered. Desorption of H2O has a low probability (less than 0.5% yield per
absorbed photon) for both types of ice. The final outcome strongly depends on
the original position of the photodissociated molecule. For molecules in the
first bilayer of crystalline ice and the corresponding layers in amorphous ice,
desorption of H atoms dominates. In the second bilayer H atom desorption,
trapping of the H and OH fragments in the ice, and recombination of H and OH
are of roughly equal importance. Deeper into the ice H atom desorption becomes
less important and trapping and recombination dominate. The distribution of
distances traveled by H atoms in the ice peaks at 6 - 7 Angstroms with a tail
going to about 60 Angstroms for both types of ice. The mobility of OH radicals
is low within the ice with most probable distances traveled of 2 and 1
Angstroms for crystalline and amorphous ice, respectively. OH is however quite
mobile on top of the surface, where it has been found to travel more than 80
Angstroms. Simulated absorption spectra of crystalline ice, amorphous ice, and
liquid water are found to be in very good agreement with experiments.
Title: Bayesian methods of astronomical source extraction Authors:Richard S. Savage Seb Oliver Comments: 11 pages; 7 figures
We present two new source extraction methods, based on the Bayesian
statistical formalism. The first is a source detection filter, able to
simultaneously detect point sources and estimate the image background. The
second is an advanced photometry technique, which measures the flux, position
(to sub-pixel accuracy), local background and point spread function of a
previously-detected source. In both cases, we use the Bayesian Information
Criterion (BIC) to compare the relative likelihood of different models. We
apply the source detection filter to simulated Herschel-SPIRE data and show the
filter's ability to both detect point sources and also simultaneously estimate
the image background. We use the photometry method to analyse a simple
simulated image containing a source of unknown flux, position and point spread
function; we not only accurately measure these parameters, but also determine
their uncertainties (using Markov-Chain Monte Carlo sampling). We also
characterise the nature of the source (for example, distinguishing between a
point source and extended source). We demonstrate the effect of including
additional prior knowledge. Prior knowledge of the point spread function
increase the precision of the flux measurement, while prior knowledge of the
background has only a small impact. In the presence of higher noise levels, we
show that prior positional knowledge (such as might arise from a strong
detection in another waveband) allows us to accurately measure the source flux
even when the source is too faint to be detected directly. These methods are
incorporated in SUSSEXtractor, the source extraction pipeline for the
forthcoming ASTRO-F FIS far-infrared all-sky survey.
Title: Nucleosynthesis of Fe60 in massive stars Authors:M. Limongi (INAF-Oar),
A. Chieffi (INAF-Iasf) Comments: 8 pages, 2 figures, in proceedings of Astronomy with Radioactivities
V, Clemson University, September 5-9, 2005, to appear in New Astronomy
Reviews
We discuss at some extent the production of Fe60 in massive stars in the
range between 11 and 120 Msun both in the hydrostatic and explosive stages. We
also compare the Fe60/Al26 gamma-ray line flux ratio obtained according to the
present calculations to the detected value reported by INTEGRAL/SPI.
Our discovery of two new satellites of Pluto, designated S/2005 P 1 and
S/2005 P 2 (henceforth, P1 and P2), combined with the constraints on the
absence of more distant satellites of Pluto, reveal that Pluto and its moons
comprise an unusual, highly compact, quadruple system. The two newly discovered
satellites of Pluto have masses that are very small compared to both Pluto and
Charon, creating a striking planet-satellite system architecture. These facts
naturally raise the question of how this puzzling satellite system came to be.
Here we show that P1 and P2's proximity to Pluto and Charon, along with their
apparent locations in high-order mean-motion resonances, likely result from
their being constructed from Plutonian collisional ejecta. We argue that
variable optical depth dust-ice rings form sporadically in the Pluto system,
and that rich satellite systems may be found, perhaps frequently, around other
large Kuiper Belt objects.
Title: Chandra and XMM-Newton Observations of a Sample of Low-Redshift FRI and
FRII Radio-Galaxy Nuclei Authors:D. A. Evans (1,2),
D. M. Worrall (1),
M. J. Hardcastle (3),
R. P. Kraft (2),
M. Birkinshaw (1) ((1) University of Bristol, (2) Harvard-Smithsonian Center for Astrophysics, (3) University of Hertfordshire) Comments: 44 pages, 5 figures. Accepted for publication in ApJ
We present spectral results, from Chandra and XMM-Newton observations, of a
sample of 22 low-redshift (z < 0.1) radio galaxies, and consider whether the
core emission originates from the base of a relativistic jet, an accretion
flow, or contains contributions from both. We find correlations between the
unabsorbed X-ray, radio, and optical fluxes and luminosities of FRI-type
radio-galaxy cores, implying a common origin in the form of a jet. On the other
hand, we find that the X-ray spectra of FRII-type radio-galaxy cores is
dominated by absorbed emission, with $N_{\rm H} > 10^{23}$ atoms cm$^{-2}$,
that is likely to originate in an accretion flow. We discuss several models
which may account for the different nuclear properties of FRI- and FRII-type
cores, and also demonstrate that both heavily obscured, accretion-related, and
unobscured, jet-related components may be present in all radio-galaxy nuclei.
Any absorbed, accretion-related, components in FRI-type galaxies have low
radiative efficiencies.
Astrophysics authors/titles "new"
Astrophysics
astro-ph new abstracts, Tue, 27 Dec 05 01:00:08 GMT
0512601 -- 0512612 received
Title: Proper-Motion Measurements of the Cygnus Egg Nebula Authors:Toshiya Ueta (USRA SOFIA/NASA Ames Research Center),
Koji Murakawa (Max-Planck Institute for Radio Astronomy),
Margaret Meixner (STScI) Comments: To appear in ApJ in April 2006. 11 ApJ emulated pages including 2
tables and 4 figures
We present the results of proper-motion measurements of the dust shell
structure in the Egg Nebula (AFGL 2688, CRL 2688, V1610 Cyg), based on the
archived two-epoch imaging-polarimetry data in the 2 micron band taken with
NICMOS on-board the Hubble Space Telescope. We measured the amount of motions
of local structures in the nebula by determining their relative shifts over an
interval of 5.5 years. The dynamical age of the nebula is found to be roughly
350 years based on the overall motion of the nebula that exhibits a
Hubble-law-esque linear relation between the measured proper motion and the
projected radial distance from the origin of the expansion. By adopting the
de-projected velocity of 45 km/s at the tips of the bipolar lobes, our
proper-motion measurements indicate that the distance to the Egg Nebula is
about 420 pc and that the lobes are inclined at 7.7 degrees with respect to the
plane of the sky. The refined distance estimate yields the luminosity of the
central star of 3.3 x 10^3 L_sun, the total shell mass of 1.2 M_sun, and the
mass loss rate (the upper limit) of 3.6 x 10^(-3) M_sun/yr. Assuming 0.6 M_sun
central post-AGB stellar mass, the initial mass of the Egg is 1.8 M_sun. Upon
analysis, we also discovered that the central star of the Egg Nebula has proper
motion of its own at the rate of (14, -10) mas/yr.
Title: Quiescent times in Gamma-Ray-Bursts: evidence of a dormant inner engine Authors:Alessandro Drago (Ferrara U. & INFN sez. Ferrara),
Giuseppe Pagliara (Torino Politecnico & INFN sez. Ferrara) Comments: 7 pages, 4 figures
The time structure of Gamma Ray Bursts (GRBs) is usually complex and it often
displays several short pulses separated by time intervals lasting from
fractions of second to several ten of seconds. A previous statistical analysis
has shown that there are three time-scales in the GRB light curves: the
shortest one is the variability scale determining the pulses' durations and the
intervals between pulses; the largest one describes the total duration of the
burst and finally, an intermediate time scale is associated with long periods
within the bursts having no activity, the so called quiescent times. Here we
show, through a statistical analysis, that if a quiescent time longer than a
few ten of seconds is present in the light curve then the pre-quiescence and
the post-quiescence emissions have similar variability scales, but the
post-quiescence emission is longer and only marginally softer than the
pre-quiescence emission. The similarities between the first and the second
emission periods strongly suggest that both emissions are produced by the same
mechanism and that long quiescent times are generated by a turning off of the
inner engine rather than by stochastic modulation of a continuous wind.
The neutron capture cross section of the unstable nucleus $^{186}$Re is
studied by investigating the inverse photodisintegration reaction
$^{187}$Re($\gamma$,n). The special interest of the {\it s}-process branching
point $^{186}$Re is related to the question of possible {\it s}-process
contributions to the abundance of the {\it r}-process chronometer nucleus
^{187}$Re. We use the photoactivation technique to measure photodisintegration
rates. Our experimental results are in good agreement with two different
statistical model calculations. Although the cross sections predicted by both
models for the inverse reaction $^{186}$Re(n,$\gamma$) is too low to remove the
overproduction of $^{186}$Os; the two predicted neutron-capture cross sections
differ by a factor of 2.4; this calls for future theoretical study.
Astrophysical neutrinos at $\sim$EeV energies promise to be an interesting
source for astrophysics and particle physics. Detecting the predicted
cosmogenic (``GZK'') neutrinos at 10$^{16}$ - 10$^{20}$ eV would test models of
cosmic ray production at these energies and probe particle physics at $\sim$100
TeV center-of-mass energy. While IceCube could detect $\sim$1 GZK event per
year, it is necessary to detect 10 or more events per year in order to study
temporal, angular, and spectral distributions. The IceCube observatory may be
able to achieve such event rates with an extension including optical, radio,
and acoustic receivers. We present results from simulating such a hybrid
detector.
Title: Structured FRW universe leads to acceleration: a non-perturbative
approach Authors:Reza Mansouri
We propose a model universe in the matter dominated phase described by a FRW
background with local inhomogeneities, like our local patch, grown out of the
primordial fluctuations. Our local patch consisting of different structures is
approximated as an inhomogeneous cosmic fluid described by a LTB metric
embedded in a background FRW universe. Within the exact general relativistic
formulation, the junction conditions for the only possible matching without a
thin shell at the boundary, neglected so far in the literature, constrains the
model in such a way that the luminosity distance-red shift relation mimics a
FRW universe with dark energy. Therefore, the dimming of SNIa is naturally
accounted for in such a {\it structured FRW} universe. The existence of the
overdense and the compensating underdense regions within the epoch of
transition at about $z = 0.5$, a consequence of the junction conditions,
explains naturally the late ISW effect and the suppression of low $l$
multipoles in CMB data. The no-go theorem does not apply here as the dynamics
of the inhomogeneous patch is compared with that of the FRW bulk. There is no
dark energy needed to interpret the acceleration. By using an exact formulation
of the general relativistic dynamics of structures in a homogeneous universe,
the claim is therefore confirmed that backreaction of cosmological
perturbations is the cause of the acceleration of the universe.
Title: Monte Carlo simulations of star clusters -- III. A million body star
cluster Authors:Mirek Giersz Comments: 12 pages, 11 figures
A revision of Stodolkiewicz's Monte Carlo code is used to simulate the
evolution of million body star clusters. The new method treats each superstar
as a single star and follows the evolution and motion of all individual stellar
objects. A survey of the evolution of N-body systems influenced by the tidal
field of a parent galaxy and by stellar evolution is presented. The process of
energy generation is realized by means of appropriately modified versions of
Spitzer's and Mikkola's formulae for the interaction cross section between
binaries and field stars and binaries themselves. The results presented are in
good agreement with theoretical expectations and the results of other methods.
During the evolution, the initial mass function (IMF) changes significantly.
The local mass function (LMF) around the half--mass radius closely resembles
the actual global mass function (GMF). At the late stages of evolution the mass
of the evolved stars inside the core can be as high as 97% of the total mass in
this region. For the whole system, the evolved stars can compose up to 67% of
the total mass. The evolution of cluster anisotropy strongly depends on initial
cluster concentration, IMF and the strength of the tidal field. The results
presented are the first step in the direction of simulating the evolution of
real globular clusters by means of the Monte Carlo method.
We analyze the peculiar velocity field for 2400 flat spiral galaxies selected
from an infrared sky survey (2MFGC). The distances to the galaxies have been
determined from the Tully-Fisher relation in the photometric J band with a
dispersion of 0.45 mag. The bulk motion of this sample relative to the cosmic
microwave background (3K) frame has an amplitude of 199+/-37 km/s in the
direction l = 290 +/- 11, b = +1 +/- 9 degree. The amplitude of the dipole
motion tends to decrease with distance in accordance with the expected
convergence of bulk flows in the 3K frame. We believe that external massive
attractors similar to the Shapley cluster concentration are responsible for
\~60% of the local flow velocity in the z = 0.03 volume.
Title: The origin and evolution of cluster magnetism Authors:A. Shukurov (Newcastle),
K. Subramanian (IUCAA),
N. E. L. Haugen (Trondheim) Comments: 4 pages, 1 figure, submitted to Astronomische Nachrichten
(proceedings of "The Origin and Evolution of Cosmic Magnetism", 29 August - 2
September 2005, Bologna, Italy)
Random motions can occur in the intergalactic gas of galaxy clusters at all
stages of their evolution. Depending on the poorly known value of the Reynolds
number, these motions can or cannot become turbulent, but in any case they can
generate random magnetic fields via dynamo action. We argue that magnetic
fields inferred observationally for the intracluster medium require dynamo
action, and then estimate parameters of random flows and magnetic fields at
various stages of the cluster evolution.
Title: Estimate black hole masses of AGNs using ultraviolet emission line
properties Authors:Min-Zhi Kong,
Xue-Bing Wu,
Ran Wang,
Jin-Lin Han Comments: 19 pages, 10 figures
Based on the measured sizes of broad line region of the reverberation-mapping
AGN sample, two new empirical relations are introduced to estimate the central
black hole masses of radio-loud high-redshift ($z > 0.5$) AGNs. First, using
the archival $IUE/HST$ spectroscopy data at UV band for the
reverberation-mapping objects, we obtained two new empirical relations between
the BLR size and \Mg/\C emission line luminosity. Secondly, using the newly
determined black hole masses of the reverberation-mapping sample for
calibration, two new relationships for determination of black hole mass with
the full width of half maximum and the luminosity of \Mg/\C line are also
found. We then apply the relations to estimate the black hole masses of AGNs in
Large Bright Quasar Surveyq and a sample of radio-loud quasars. For the objects
with small radio-loudness, the black hole mass estimated using the $R_{\rm BLR}
- L_{\eMg/\eC}$ relation is consistent with that from the $R_{BLR} -
L_{3000\AA/1350 \AA}$ relation. But for radio-loud AGNs, the mass estimated
from the $R_{BLR} - L_{\eMg/\eC}$ relation is systematically lower than that
from the continuum luminosity $L_{3000\AA/1350\AA}$. Because jets could have
significant contributions to the UV/optical continuum luminosity of radio-loud
AGNs, we emphasized again that for radio-loud AGNs, the emission line
luminosity may be a better tracer of the ionizing luminosity than the continuum
luminosity, so that the relations between the BLR size and UV emission line
luminosity should be used to estimate the black hole masses of high redshift
radio-loud AGNs.
Title: Physical and chemical structure of dense cores in regions of high mass
star formation Authors:Igor Zinchenko,
Lev Pirogov,
Paola Caselli,
Lars E.B. Johansson,
Sergey Malafeev,
Barry Turner Comments: 6 pages, 4 figures, to be published in "Massive star birth: A
crossroads of Astrophysics", IAU Symposium Proceedings of the international
Astronomical Union 227, Held 16-20 May, Italy, edited by Cesaroni, R.; Felli,
M.; Churchwell, E.; Walmsley, M. Cambridge: Cambridge University Press, 2005
We found that in regions of high mass star formation the CS emission
correlates well with the dust continuum emission and is therefore a good tracer
of the total mass while the N$_2$H$^+$ distribution is frequently very
different. This is opposite to their typical behavior in low-mass cores where
freeze-out plays a crucial role in the chemistry. The behavior of other high
density tracers varies from source to source but most of them are closer to CS.
Radial density profiles in massive cores are fitted by power laws with indices
about -1.6, as derived from the dust continuum emission. The radial temperature
dependence on intermediate scales is close to the theoretically expected one
for a centrally heated optically thin cloud. The velocity dispersion either
remains constant or decreases from the core center to the edge. Several cores
including those without known embedded IR sources show signs of infall motions.
They can represent the earliest phases of massive protostars. There are
implicit arguments in favor of small-scale clumpiness in the cores.
Title: Phase-Space Distributions of Chemical Abundances in Milky Way-type
Galaxy Halos Authors:Andreea S. Font (1),
Kathryn V. Johnston (1),
James S. Bullock (2),
Brant E. Robertson (3) ((1) Wesleyan University; (2) University of California, Irvine; (3) Harvard/CfA) Comments: submitted to ApJ. High res figures can be found at:
this http URL
[Abridged] Motivated by upcoming data from astrometric and spectroscopic
surveys of the Galaxy, we explore the chemical abundance properties and
phase-space distributions in hierarchically-formed stellar halo simulations set
in a LambdaCDM Universe. Our sample of Milky-Way type stellar halo simulations
result in average metallicities that range from [Fe/H] = -1.3 to -0.9, with the
most metal poor halos resulting from accretion histories that lack destructive
mergers with massive (metal rich) satellites. Our stellar halo metallicities
increase with stellar halo mass. The slope of the [Fe/H]-stellar mass trend
mimics that of the satellite galaxies that were destroyed to build the halos,
implying that the relation propagates hierarchically. All simulated halos
contain a significant fraction of old stellar populations accreted more than 10
Gyr ago and in a few cases, some intermediate age populations exist. In
contrast with the Milky Way, many of our simulated stellar halos contain old
stellar populations which are metal rich, originating in the early accretion of
massive satellites. We suggest that the (metal rich) stellar halo of M31 falls
into this category, while the more metal poor halo of the Milky Way is lacking
in early massive accretion events. Interestingly, our hierarchically-formed
stellar halos often have non-negligible metallicity gradients in both [Fe/H]
and [alpha/Fe]. These gradients extend a few tens of kpc, and can be as large
as 0.5 dex in [Fe/H] and 0.2 dex in [alpha/Fe]. Finally, we find that chemical
abundances can act as a rough substitute for time of accretion of satellite
galaxies. We propose a criterion for identifying tidal streams spatially by
selecting stars with [alpha/Fe] ratios below solar.
Title: Flat Cosmology with Interacting Matter and Dark Energies Authors:A.-M.M. Abdel-Rahman,
Ihab F. Riad, (Department of Physics, Faculty of Science, University of Khartoum, Khartoum, Sudan)
Three models of a flat universe of interacting matter and dark energies with
different low-redshift parameterizations of the dark energy equation of state
are considered. The dark energy is assumed to vary with time like the trace of
the energy-momentum tensor of cosmic matter. In the radiation-dominated era the
models reduce to standard cosmology. In the matter-dominated era they are, for
often quoted values of the cosmological parameters, consistent with data from
supernovae Ia searches and with the data of Gurvits et al.(1999) for angular
sizes of ultra compact radio sources.
Astrophysics authors/titles "new"
Astrophysics
astro-ph new abstracts, Tue, 27 Dec 05 01:00:08 GMT
0512601 -- 0512612 received
Title: Proper-Motion Measurements of the Cygnus Egg Nebula Authors:Toshiya Ueta (USRA SOFIA/NASA Ames Research Center),
Koji Murakawa (Max-Planck Institute for Radio Astronomy),
Margaret Meixner (STScI) Comments: To appear in ApJ in April 2006. 11 ApJ emulated pages including 2
tables and 4 figures
We present the results of proper-motion measurements of the dust shell
structure in the Egg Nebula (AFGL 2688, CRL 2688, V1610 Cyg), based on the
archived two-epoch imaging-polarimetry data in the 2 micron band taken with
NICMOS on-board the Hubble Space Telescope. We measured the amount of motions
of local structures in the nebula by determining their relative shifts over an
interval of 5.5 years. The dynamical age of the nebula is found to be roughly
350 years based on the overall motion of the nebula that exhibits a
Hubble-law-esque linear relation between the measured proper motion and the
projected radial distance from the origin of the expansion. By adopting the
de-projected velocity of 45 km/s at the tips of the bipolar lobes, our
proper-motion measurements indicate that the distance to the Egg Nebula is
about 420 pc and that the lobes are inclined at 7.7 degrees with respect to the
plane of the sky. The refined distance estimate yields the luminosity of the
central star of 3.3 x 10^3 L_sun, the total shell mass of 1.2 M_sun, and the
mass loss rate (the upper limit) of 3.6 x 10^(-3) M_sun/yr. Assuming 0.6 M_sun
central post-AGB stellar mass, the initial mass of the Egg is 1.8 M_sun. Upon
analysis, we also discovered that the central star of the Egg Nebula has proper
motion of its own at the rate of (14, -10) mas/yr.
Title: Quiescent times in Gamma-Ray-Bursts: evidence of a dormant inner engine Authors:Alessandro Drago (Ferrara U. & INFN sez. Ferrara),
Giuseppe Pagliara (Torino Politecnico & INFN sez. Ferrara) Comments: 7 pages, 4 figures
The time structure of Gamma Ray Bursts (GRBs) is usually complex and it often
displays several short pulses separated by time intervals lasting from
fractions of second to several ten of seconds. A previous statistical analysis
has shown that there are three time-scales in the GRB light curves: the
shortest one is the variability scale determining the pulses' durations and the
intervals between pulses; the largest one describes the total duration of the
burst and finally, an intermediate time scale is associated with long periods
within the bursts having no activity, the so called quiescent times. Here we
show, through a statistical analysis, that if a quiescent time longer than a
few ten of seconds is present in the light curve then the pre-quiescence and
the post-quiescence emissions have similar variability scales, but the
post-quiescence emission is longer and only marginally softer than the
pre-quiescence emission. The similarities between the first and the second
emission periods strongly suggest that both emissions are produced by the same
mechanism and that long quiescent times are generated by a turning off of the
inner engine rather than by stochastic modulation of a continuous wind.
The neutron capture cross section of the unstable nucleus $^{186}$Re is
studied by investigating the inverse photodisintegration reaction
$^{187}$Re($\gamma$,n). The special interest of the {\it s}-process branching
point $^{186}$Re is related to the question of possible {\it s}-process
contributions to the abundance of the {\it r}-process chronometer nucleus
^{187}$Re. We use the photoactivation technique to measure photodisintegration
rates. Our experimental results are in good agreement with two different
statistical model calculations. Although the cross sections predicted by both
models for the inverse reaction $^{186}$Re(n,$\gamma$) is too low to remove the
overproduction of $^{186}$Os; the two predicted neutron-capture cross sections
differ by a factor of 2.4; this calls for future theoretical study.
Astrophysical neutrinos at $\sim$EeV energies promise to be an interesting
source for astrophysics and particle physics. Detecting the predicted
cosmogenic (``GZK'') neutrinos at 10$^{16}$ - 10$^{20}$ eV would test models of
cosmic ray production at these energies and probe particle physics at $\sim$100
TeV center-of-mass energy. While IceCube could detect $\sim$1 GZK event per
year, it is necessary to detect 10 or more events per year in order to study
temporal, angular, and spectral distributions. The IceCube observatory may be
able to achieve such event rates with an extension including optical, radio,
and acoustic receivers. We present results from simulating such a hybrid
detector.
Title: Structured FRW universe leads to acceleration: a non-perturbative
approach Authors:Reza Mansouri
We propose a model universe in the matter dominated phase described by a FRW
background with local inhomogeneities, like our local patch, grown out of the
primordial fluctuations. Our local patch consisting of different structures is
approximated as an inhomogeneous cosmic fluid described by a LTB metric
embedded in a background FRW universe. Within the exact general relativistic
formulation, the junction conditions for the only possible matching without a
thin shell at the boundary, neglected so far in the literature, constrains the
model in such a way that the luminosity distance-red shift relation mimics a
FRW universe with dark energy. Therefore, the dimming of SNIa is naturally
accounted for in such a {\it structured FRW} universe. The existence of the
overdense and the compensating underdense regions within the epoch of
transition at about $z = 0.5$, a consequence of the junction conditions,
explains naturally the late ISW effect and the suppression of low $l$
multipoles in CMB data. The no-go theorem does not apply here as the dynamics
of the inhomogeneous patch is compared with that of the FRW bulk. There is no
dark energy needed to interpret the acceleration. By using an exact formulation
of the general relativistic dynamics of structures in a homogeneous universe,
the claim is therefore confirmed that backreaction of cosmological
perturbations is the cause of the acceleration of the universe.
Title: Monte Carlo simulations of star clusters -- III. A million body star
cluster Authors:Mirek Giersz Comments: 12 pages, 11 figures
A revision of Stodolkiewicz's Monte Carlo code is used to simulate the
evolution of million body star clusters. The new method treats each superstar
as a single star and follows the evolution and motion of all individual stellar
objects. A survey of the evolution of N-body systems influenced by the tidal
field of a parent galaxy and by stellar evolution is presented. The process of
energy generation is realized by means of appropriately modified versions of
Spitzer's and Mikkola's formulae for the interaction cross section between
binaries and field stars and binaries themselves. The results presented are in
good agreement with theoretical expectations and the results of other methods.
During the evolution, the initial mass function (IMF) changes significantly.
The local mass function (LMF) around the half--mass radius closely resembles
the actual global mass function (GMF). At the late stages of evolution the mass
of the evolved stars inside the core can be as high as 97% of the total mass in
this region. For the whole system, the evolved stars can compose up to 67% of
the total mass. The evolution of cluster anisotropy strongly depends on initial
cluster concentration, IMF and the strength of the tidal field. The results
presented are the first step in the direction of simulating the evolution of
real globular clusters by means of the Monte Carlo method.
We analyze the peculiar velocity field for 2400 flat spiral galaxies selected
from an infrared sky survey (2MFGC). The distances to the galaxies have been
determined from the Tully-Fisher relation in the photometric J band with a
dispersion of 0.45 mag. The bulk motion of this sample relative to the cosmic
microwave background (3K) frame has an amplitude of 199+/-37 km/s in the
direction l = 290 +/- 11, b = +1 +/- 9 degree. The amplitude of the dipole
motion tends to decrease with distance in accordance with the expected
convergence of bulk flows in the 3K frame. We believe that external massive
attractors similar to the Shapley cluster concentration are responsible for
\~60% of the local flow velocity in the z = 0.03 volume.
Title: The origin and evolution of cluster magnetism Authors:A. Shukurov (Newcastle),
K. Subramanian (IUCAA),
N. E. L. Haugen (Trondheim) Comments: 4 pages, 1 figure, submitted to Astronomische Nachrichten
(proceedings of "The Origin and Evolution of Cosmic Magnetism", 29 August - 2
September 2005, Bologna, Italy)
Random motions can occur in the intergalactic gas of galaxy clusters at all
stages of their evolution. Depending on the poorly known value of the Reynolds
number, these motions can or cannot become turbulent, but in any case they can
generate random magnetic fields via dynamo action. We argue that magnetic
fields inferred observationally for the intracluster medium require dynamo
action, and then estimate parameters of random flows and magnetic fields at
various stages of the cluster evolution.
Title: Estimate black hole masses of AGNs using ultraviolet emission line
properties Authors:Min-Zhi Kong,
Xue-Bing Wu,
Ran Wang,
Jin-Lin Han Comments: 19 pages, 10 figures
Based on the measured sizes of broad line region of the reverberation-mapping
AGN sample, two new empirical relations are introduced to estimate the central
black hole masses of radio-loud high-redshift ($z > 0.5$) AGNs. First, using
the archival $IUE/HST$ spectroscopy data at UV band for the
reverberation-mapping objects, we obtained two new empirical relations between
the BLR size and \Mg/\C emission line luminosity. Secondly, using the newly
determined black hole masses of the reverberation-mapping sample for
calibration, two new relationships for determination of black hole mass with
the full width of half maximum and the luminosity of \Mg/\C line are also
found. We then apply the relations to estimate the black hole masses of AGNs in
Large Bright Quasar Surveyq and a sample of radio-loud quasars. For the objects
with small radio-loudness, the black hole mass estimated using the $R_{\rm BLR}
- L_{\eMg/\eC}$ relation is consistent with that from the $R_{BLR} -
L_{3000\AA/1350 \AA}$ relation. But for radio-loud AGNs, the mass estimated
from the $R_{BLR} - L_{\eMg/\eC}$ relation is systematically lower than that
from the continuum luminosity $L_{3000\AA/1350\AA}$. Because jets could have
significant contributions to the UV/optical continuum luminosity of radio-loud
AGNs, we emphasized again that for radio-loud AGNs, the emission line
luminosity may be a better tracer of the ionizing luminosity than the continuum
luminosity, so that the relations between the BLR size and UV emission line
luminosity should be used to estimate the black hole masses of high redshift
radio-loud AGNs.
Title: Physical and chemical structure of dense cores in regions of high mass
star formation Authors:Igor Zinchenko,
Lev Pirogov,
Paola Caselli,
Lars E.B. Johansson,
Sergey Malafeev,
Barry Turner Comments: 6 pages, 4 figures, to be published in "Massive star birth: A
crossroads of Astrophysics", IAU Symposium Proceedings of the international
Astronomical Union 227, Held 16-20 May, Italy, edited by Cesaroni, R.; Felli,
M.; Churchwell, E.; Walmsley, M. Cambridge: Cambridge University Press, 2005
We found that in regions of high mass star formation the CS emission
correlates well with the dust continuum emission and is therefore a good tracer
of the total mass while the N$_2$H$^+$ distribution is frequently very
different. This is opposite to their typical behavior in low-mass cores where
freeze-out plays a crucial role in the chemistry. The behavior of other high
density tracers varies from source to source but most of them are closer to CS.
Radial density profiles in massive cores are fitted by power laws with indices
about -1.6, as derived from the dust continuum emission. The radial temperature
dependence on intermediate scales is close to the theoretically expected one
for a centrally heated optically thin cloud. The velocity dispersion either
remains constant or decreases from the core center to the edge. Several cores
including those without known embedded IR sources show signs of infall motions.
They can represent the earliest phases of massive protostars. There are
implicit arguments in favor of small-scale clumpiness in the cores.
Title: Phase-Space Distributions of Chemical Abundances in Milky Way-type
Galaxy Halos Authors:Andreea S. Font (1),
Kathryn V. Johnston (1),
James S. Bullock (2),
Brant E. Robertson (3) ((1) Wesleyan University; (2) University of California, Irvine; (3) Harvard/CfA) Comments: submitted to ApJ. High res figures can be found at:
this http URL
[Abridged] Motivated by upcoming data from astrometric and spectroscopic
surveys of the Galaxy, we explore the chemical abundance properties and
phase-space distributions in hierarchically-formed stellar halo simulations set
in a LambdaCDM Universe. Our sample of Milky-Way type stellar halo simulations
result in average metallicities that range from [Fe/H] = -1.3 to -0.9, with the
most metal poor halos resulting from accretion histories that lack destructive
mergers with massive (metal rich) satellites. Our stellar halo metallicities
increase with stellar halo mass. The slope of the [Fe/H]-stellar mass trend
mimics that of the satellite galaxies that were destroyed to build the halos,
implying that the relation propagates hierarchically. All simulated halos
contain a significant fraction of old stellar populations accreted more than 10
Gyr ago and in a few cases, some intermediate age populations exist. In
contrast with the Milky Way, many of our simulated stellar halos contain old
stellar populations which are metal rich, originating in the early accretion of
massive satellites. We suggest that the (metal rich) stellar halo of M31 falls
into this category, while the more metal poor halo of the Milky Way is lacking
in early massive accretion events. Interestingly, our hierarchically-formed
stellar halos often have non-negligible metallicity gradients in both [Fe/H]
and [alpha/Fe]. These gradients extend a few tens of kpc, and can be as large
as 0.5 dex in [Fe/H] and 0.2 dex in [alpha/Fe]. Finally, we find that chemical
abundances can act as a rough substitute for time of accretion of satellite
galaxies. We propose a criterion for identifying tidal streams spatially by
selecting stars with [alpha/Fe] ratios below solar.
Title: Flat Cosmology with Interacting Matter and Dark Energies Authors:A.-M.M. Abdel-Rahman,
Ihab F. Riad, (Department of Physics, Faculty of Science, University of Khartoum, Khartoum, Sudan)
Three models of a flat universe of interacting matter and dark energies with
different low-redshift parameterizations of the dark energy equation of state
are considered. The dark energy is assumed to vary with time like the trace of
the energy-momentum tensor of cosmic matter. In the radiation-dominated era the
models reduce to standard cosmology. In the matter-dominated era they are, for
often quoted values of the cosmological parameters, consistent with data from
supernovae Ia searches and with the data of Gurvits et al.(1999) for angular
sizes of ultra compact radio sources.
Title: A Deep Radio Survey of Abell 2125 III: The Cluster Core - Merging and
Stripping
Authors: F. N. Owen (NRAO),
W. C. Keel (Alabama),
Q. D. Wang (UMass),
M. J. Ledlow (Gemini),
G.E. Morrison (NOAO)
Comments: 36 pages, 16 figures, accepted AJ, paper with full resolution figures
is available at http:www.aoc.nrao.edu/~fowen/papers/a2125/a2125paper3.ps.gz
We use radio, near-IR, optical, and X-ray observations to examine dynamic
processes in the central region of Abell 2125. In addition to the central
triple, including members of both major dynamical subsystems identified from a
redshift survey, this region features a galaxy showing strong evidence for
ongoing gas stripping during a high-velocity passage through the gas in the
cluster core. The disk galaxy C153 exhibits a plume stretching toward the
cluster center seen in soft X-rays by Chandra, parts of which are also seen in
[O II] emission and near-UV continuum light. HST imaging shows a distorted
disk, with star-forming knots asymmetrically distributed and remnant spiral
structure possibly defined by dust lanes. The stars and ionized gas in its disk
are kinematically decoupled, demonstrating that pressure stripping must be
important, and that tidal disruption is not the only mechanism at work.
Comparison of the gas properties seen in the X-ray and optical data on the
plume highlight significant features of the history of stripped gas in the
intracluster medium. The nucleus of C153 also hosts an AGN, shown by the weak
and distorted extended radio emission and a radio compact core. The unusual
strength of the stripping signatures in this instance is likely related to the
high relative velocity of the galaxy with respect to the intracluster medium,
during a cluster/cluster merger, and its passage very near the core of the
cluster. Another sign of recent dynamical events is diffuse starlight
asymmetrically placed about the central triple in a cD envelope. Transient and
extreme dynamical events as seen in Abell 2125 may be important drivers of
galaxy evolution in the cores of rich clusters.
Title: Einstein's Geometrization vs. Spatial Coordinate-rescale Cancellation of
Static Gravity
Authors: Jin He
Comments: 14 pages; Note that you do not mail any comment to the affiliation.
The author may be jobless
Particle's acceleration in static homogeneous gravitational field is
cancelled by any freely-falling frame. The present paper shows that the
acceleration is also cancelled by a spatial curvilinear coordinate system. The
coordinate system is simply a spatial square-root coordinate rescale in the
field direction, no relative motion being involved. In an inhomogeneous
gravitational field, no such freely-falling frame can be found. However, the
present paper shows that spatial radial coordinate-rescales which cancel
gravity are still there for several cases of inhomogeneous static gravity. This
suggests that spacetime is flat which has inertial frame of Minkowski metric
$\eta_{ij}$. Gravity is a tensor $g_{\alpha \beta}$ on the spacetime, which is
called effective metric. The effective metric emerges from the coordinate
rescale. The gravitational field of an isolated point mass requires a radial
translational coordinate rescale. The corresponding effective metric is
different from that of Schwarzchild. To first order, its prediction on the
deflection of light and the precession of the perihelia of planetary orbits is
the same as the one of general relativity (GR). However, the metric has the
important prediction that the common angular momentum is not conserved.
Instead, the shadow angular momentum is conserved. Because the distance between
a point and its shadow is $GM/c^2$ ($\approx $ 1.5km for the mass of sun), the
test on the prediction needs high precision solar or other observations and is
left for future work.
Until recently, X-ray flares during the afterglow of gamma ray bursts (GRBs)
were a rarely detected phenomenon, thus their nature is unclear. During the
afterglow of GRB 050502B, the largest X-ray flare ever recorded rose rapidly
above the afterglow lightcurve detected by the Swift X-ray Telescope. The peak
flux of the flare was >500 times that of the underlying afterglow, and it
occurred at >12 minutes after the nominal prompt burst emission. The fluence of
this X-ray flare, (1.0 +/- 0.05) x 10^{-6} erg cm^{-2} in the 0.2-10.0 keV
energy band, exceeded the fluence of the nominal prompt burst. The spectra
during the flare were significantly harder than those measured before and after
the flare. Later in time, there were additional flux increases detected above
the underlying afterglow, as well as a break in the afterglow lightcurve. All
evidence presented below, including spectral and particularly timing
information during and around the giant flare, suggests that this giant flare
was the result of internal dissipation of energy due to late central engine
activity, rather than an afterglow-related effect. We also find that the data
are consistent with a second central engine activity episode, in which the
ejecta is moving slower than that of the initial episode, causing the giant
flare and then proceeding to overtake and refresh the afterglow shock, thus
causing additional activity at even later times in the lightcurve.
In this work we present a sensitive and systematic single-dish survey of CCS
emission (complemented with ammonia observations) at 1 cm, toward a sample of
low- and intermediate-mass young star forming regions known to harbor water
maser emission, made with NASA's 70 m antenna at Robledo de Chavela, Spain.
Out of the 40 star forming regions surveyed in the CCS(2_{1}-1_{0}) line,
only 6 low-mass sources show CCS emission: one transitional object between
pre-stellar and protostellar Class 0 phase (GF9-2), three Class 0 protostars
(L1448-IRS3, L1448C, and B1-IRS), a Class I source (L1251A), and a young T
Tauri star (NGC2071-North). Since CCS is considered an ``early-time'' (<10E+5
yr) molecule, we explain these results by either proposing a revision of the
classification of the age of NGC2071-North and L1251A, or suggesting the
possibility that the particular physical conditions and processes of each
source affect the destruction/production of the CCS. No statistically
significant relationship was found between the presence of CCS and parameters
of the molecular outflows and their driving sources. Nevertheless, we found a
significant relationship between the detectability of CCS and the ammonia peak
intensity (higher in regions with CCS), but not with its integrated intensity.
This tendency found may suggest that the narrower ammonia line widths in the
less turbulent medium associated with younger cores may compensate for the
differences in ammonia peak intensity, rendering differences in integrated
intensity negligible. From the CCS detection rate we derive a lifetime of this
molecule of ~(0.7-3) x 10E+4 yr in low-mass star forming regions.
HH 110 and HH 262 are two Herbig-Haro jets with rather peculiar, chaotic
morphology. In the two cases, no source suitable to power the jet has been
detected along the outflow, at optical or radio wavelengths. Both, previous
data and theoretical models, suggest that these objects are tracing an early
stage of an HH jet/dense cloud interaction. We present the first results of the
integral field spectroscopy observations made with the PMAS spectrophotometer
(with the PPAK configuration) of these two turbulent jets. New data of the
kinematics in several characteristic HH emission lines are shown. In addition,
line-ratio maps have been made, suitable to explore the spatial excitation an
density conditions of the jets as a function of their kinematics.
Mid-infrared observations of Active Galactic Nuclei (AGN) are important for
understanding of the physical conditions around the central accretion engines.
Chandra and XMM-Newton X-ray observations of a 300 arcmin^2 region in the
Extended Groth Strip are used to select a sample of~150 AGN. The Spitzer
instruments IRAC and MIPS detect 68-80% of these sources, which show a wide
range of mid-infrared properties. About 40% of the sources have red power-law
spectral energy distributions (f_nu ~ nu^alpha, alpha<0) in the 3.6-8 um IRAC
bands. In these sources the central engine dominates the emission at both X-ray
and IR wavelengths. Another 40% of the sources have blue mid-IR spectral energy
distributions (alpha>0) with their infrared emission dominated by the host
galaxy; the remaining 20% are not well-fit by a power law. Published IRAC color
criteria for AGN select most of the red sources, but only some of the blue
sources. As with all other known methods, selecting AGN with mid-IR colors will
not produce a sample that is simultaneously complete and reliable. The IRAC SED
type does not directly correspond to X-ray spectral type (hard/soft). The
mid-IR properties of X-ray-detected Lyman-break, radio, submillimeter, and
optically-faint sources vary widely and, for the most part, are not distinct
from those of the general X-ray/infrared source population. X-ray sources emit
6-11% of the integrated mid--IR light, making them significant contributors to
the cosmic infrared background.
We have carried out a spectroscopic survey of several B, Be, and shell stars
in optical and near-infrared regions. Line profiles of the H-alpha line and of
selected Fe II and O I lines are presented.
Title: Assisted stellar suicide in V617 Sgr
Authors: J. E. Steiner (IAG-USP),
A. S. Oliveira (SOAR Telescope),
D. Cieslinski (INPE),
T. V. Ricci (IAG-USP)
Comments: 4 pages, accepted for publication in A&A Letters
V617 Sgr is a V Sagittae star - a group of binaries thought to be the
galactic counterparts of the Compact Binary Supersoft X-ray Sources - CBSS. To
check this hypothesis, we measured the time derivative of its orbital period.
Observed timings of eclipse minima spanning over 30,000 orbital cycles are
presented. We found that the orbital period evolves quite rapidly: P/Pdot = 1.1
x 10^{6} years. This is consistent with the idea that V617 Sgr is a wind driven
accretion supersoft source. As the binary system evolves with a time-scale of
about one million years, which is extremely short for a low mass evolved
binary, it is likely that the system will soon end either by having its
secondary completely evaporated or by the primary exploding as a supernova of
type Ia.
Title: Astrometric Monitoring of Stellar Orbits at the Galactic Center with a
Next Generation Large Telescope
Authors: Nevin N. Weinberg (1, 2),
Milos Milosavljevic (1),
Andrea M. Ghez (3) ((1) Caltech, (2) KITP, (3) UCLA)
Comments: 8 pages, 3 figures. ASP Conf. Series "Astrometry in the Age of the
Next Generation of Large Telescopes", 2005, v.338, eds. P. Kenneth Seidelmann
and Alice K. B. Monet
Journal-ref: ASP Conf. Proc. 338 (2005) 252
We show that with a Next Generation Large Telescope one can detect the
accelerated motions of ~100 stars orbiting the massive black hole at the
Galactic center. The positions and velocities of these stars will be measured
to astrometric and spectroscopic precision several times better than currently
attainable enabling detailed measurements of the gravitational potential in the
neighborhood of the massive black hole. We show that the monitoring of stellar
motions with such a telescopes enables: (1) a measurement of the Galactic
center distance R_0 to better than 0.1% accuracy, (2) a measurement of the
extended matter distribution near the black hole, including that of the exotic
dark matter, (3) a detection of general relativistic effects due to the black
hole including the prograde precession of stars and possibly the black hole
spin, and (4) a detection of gravitational encounters between monitored stars
and stellar remnants that accumulate near the Galactic center. Such encounters
probe the mass function of the remnants.
Title: "Expansion" around the vacuum: how far can we go from Lambda?
Authors: J.S. Alcaniz,
H. Stefancic
Comments: 7 pages, 3 figures, LaTeX
The cosmological constant ($\Lambda$), i.e., the energy density stored in the
true vacuum state of all existing fields in the Universe, is the simplest and
the most natural possibility to describe the current cosmic acceleration.
However, despite its observational successes, such a possibility exacerbates
the well known $\Lambda$ problem, requiring a natural explanation for its
small, but nonzero, value. In this paper we discuss how different our Universe
may be from the $\Lambda$CDM model by studying observational aspects of a kind
of "expansion" around the vacuum given by the equation of (EOS)
$p_{d}=-\rho_{d} - A \rho_{d}^{\alpha}$. In different parameter regimes such a
parametrization is capable of describing both quintessence-like and phantom
like dark energy, transient acceleration, and various (non)singular
possibilities for the final destiny of the Universe, including singularities at
finite values of the scale factor, the so-called "Big Rip", as well as sudden
future singularities. By using some of the most recent cosmological
observations we show that if the functional form of the dark energy EOS has
additional parameters very little can be said about their values from the
current observational results, which postpones, until the arrival of more
precise observational data, a definitive answer to the question posed above.
We present a spectroscopic survey using the MMT/Hectospec fiber spectrograph
of 24 micron sources selected with the Spitzer Space Telescope in the Spitzer
First Look Survey. We report 1295 new redshifts for 24 micron sources,
including 598 with f(24um) > 1 mJy. Combined with 291 additional redshifts for
sources from the Sloan Digital Sky Survey (SDSS) our observing program was
highly efficient and is ~90% complete for i < 21 mag and f(24um) > 1 mJy, and
is 37% complete for i < 20.5 mag and 0.3 mJy < f(24um) < 1 mJy. Our Hectospec
survey includes 1065 and 176 objects spectroscopically classified as galaxies
and QSOs, respectively. Combining the Hectospec and SDSS samples, we find
galaxies to z(gal) < 0.98 and QSOs to z(QSO) < 3.6, with mean redshifts of
<z(gal)>=0.27 and <z(QSO)>=1.1. As part of this paper, we publish the redshift
catalogs and the reduced spectra.
Title: X-ray flare modeling in the single giant HR 9024
Authors: Paola Testa (MIT),
David Garcia-Alvarez (SAO),
Fabio Reale (Univ. Palermo),
David Huenemoerder (MIT)
Comments: 2 pages, 4 figures. To be included in the proceedings of the 'X-ray
universe 2005 meeting' held in San Lorenzo de El Escorial (Spain), 26-30 Sep
2005
We analyze a Chandra-HETGS observation of the single G-type giant HR 9024.
The high flux allows us to examine spectral line and continuum diagnostics at
high temporal resolution, to derive plasma parameters (thermal distribution,
abundances, temperature, ...). A time-dependent 1D hydrodynamic loop model with
semi-length 10$^{12}$cm ($\sim R_{\star}$), and impulsive footpoint heating
triggering the flare, satisfactorily reproduces the observed evolution of
temperature and emission measure, derived from the analysis of the strong
continuum emission. The observed characteristics of the flare appear to be
common features in very large flares in active stars (also pre-main sequence
stars), possibly indicating some fundamental physics for these very dynamic and
extreme phenomena in stellar coronae.
We have performed monitoring observations of the flux density toward the
Galactic center compact radio source, Sagittarius A* (Sgr A*), which is a
supermassive black hole, from 1996 to 2005 using the Nobeyama Millimeter Array
of the Nobeyama Radio Observatory, Japan. These monitoring observations of Sgr
A* were carried out in the 3- and 2-mm (100 and 140 GHz) bands, and we have
detected several flares of Sgr A*. We found intraday variation of Sgr A* in the
2000 March flare. The twofold increase timescale is estimated to be about 1.5
hr at 140 GHz. This intraday variability suggests that the physical size of the
flare-emitting region is compact on a scale at or below about 12 AU (~150 Rs;
Schwarzschild radius). On the other hand, clear evidence of long-term periodic
variability was not found from a periodicity analysis of our current millimeter
data set.
Title: The early reionization with the primordial magnetic fields
Authors: Hiroyuki Tashiro,
Naoshi Sugiyama
Comments: 8 pages, 5 figures. Submitted to MNRAS
The early reionization of the intergalactic medium, which is favored from the
WMAP temperature-polarization cross-correlations, contests the validity of the
standard scenario of structure formation in the cold dark matter cosmogony. It
is difficult to achieve early enough star formation without rather extreme
assumptions such as very high escape fraction of ionizing photons from
proto-galaxies or a top-heavy initial mass function. Here we propose an
alternative scenario that is additional fluctuations on small scales induced by
primordial magnetic fields trigger the early structure formation. We found that
ionizing photons from Population III stars formed in dark haloes can easily
reionize the universe by $z \simeq 15$ if the strength of primordial magnetic
fields is larger than $0.6 \times 10^{-9}$Gauss.
We report the detection of hard X-ray emission from the field of the
star-forming region NGC 6334 with the the International Gamma-Ray Astrophysics
Laboratory INTEGRAL. The JEM-X monitor and ISGRI imager aboard INTEGRAL and
Chandra ACIS imager were used to construct 3-80 keV images and spectra of NGC
6334. The 3-10 keV and 10-35 keV images made with JEM-X show a complex
structure of extended emission from NGC 6334. The ISGRI source detected in the
energy ranges 20-40 keV and 40-80 keV coincides with the NGC 6334 ridge. The
20-60 keV flux from the source is (1.8+-0.37)*10(-11) erg cm(-2) s(-1).
Spectral analysis of the source revealed a hard power-law component with a
photon index about 1. The observed X-ray fluxes are in agreement with
extrapolations of X-ray imaging observations of NGC 6334 by Chandra ACIS and
ASCA GIS. The X-ray data are consistent with two very different physical
models. A probable scenario is emission from a heavily absorbed, compact and
hard Chandra source that is associated with the AGN candidate radio source NGC
6334B. Another possible model is the extended Chandra source of nonthermal
emission from NGC 6334 that can also account for the hard X-ray emission
observed by INTEGRAL. The origin of the emission in this scenario is due to
electron acceleration in energetic outflows from massive early type stars. The
possibility of emission from a young supernova remnant, as suggested by earlier
infrared observations of NGC 6334, is constrained by the non-detection of 44Ti
lines.
We report on a multiwavelength campaign on the TeV gamma-ray blazar Markarian
(Mrk) 421 performed during December 2002 and January 2003. These target of
opportunity observations were initiated by the detection of X-ray and TeV
gamma-ray flares with the All Sky Monitor (ASM) on board the Rossi X-ray Timing
Explorer (RXTE) and the 10~m Whipple gamma-ray telescope.The campaign included
observational coverage in the radio (University of Michigan Radio Astronomy
Observatory), optical (Boltwood, La Palma KVA 0.6m, WIYN 0.9m), X-ray (RXTE
pointed telescopes), and TeV gamma-ray (Whipple and HEGRA) bands.
At TeV energies, the observations revealed several flares at intermediate
flux levels, peaking between 1 and 1.5 times the flux from the Crab Nebula.
While the time averaged spectrum can be fitted with a single power law of
photon index Gamma =2.8, we find some evidence for spectral variability.
Confirming earlier results, the campaign reveals a rather loose correlation
between the X-ray and TeV gamma-ray fluxes. In one case, a very strong X-ray
flare is not accompanied by a comparable TeV gamma-ray flare. Although the
source flux was variable in the optical and radio bands, the sparse sampling of
the optical and radio light curves does not allow us to study the correlation
properties in detail.
We present a simple analysis of the data with a synchrotron-self Compton
model, emphasizing that models with very high Doppler factors and low magnetic
fields can describe the data.
Title: Nonlinear Criterion for the Stability of Molecular Clouds
Authors: Ruben Krasnopolsky,
Charles F. Gammie
Comments: 11 pages, 5 figures
Journal-ref: Astrophys.J. 635 (2005) 1126-1135
Dynamically significant magnetic fields are routinely observed in molecular
clouds, with mass-to-flux ratio lambda = (2 pi sqrt{G}) (Sigma/B) ~ 1 (here
Sigma is the total column density and B is the field strength). It is widely
believed that ``subcritical'' clouds with lambda < 1 cannot collapse, based on
virial arguments by Mestel and Spitzer and a linear stability analysis by
Nakano and Nakamura. Here we confirm, using high resolution numerical models
that begin with a strongly supersonic velocity dispersion, that this criterion
is a fully nonlinear stability condition. All the high-resolution models with
lambda <= 0.95 form ``Spitzer sheets'' but collapse no further. All models with
lambda >= 1.02 collapse to the maximum numerically resolvable density. We also
investigate other factors determining the collapse time for supercritical
models. We show that there is a strong stochastic element in the collapse time:
models that differ only in details of their initial conditions can have
collapse times that vary by as much as a factor of 3. The collapse time cannot
be determined from just the velocity dispersion; it depends also on its
distribution. Finally, we discuss the astrophysical implications of our
results.
Title: Detection with RHESSI of high frequency X-ray oscillations in the tail
of the 2004 hyperflare from SGR 1806-20
Authors: Anna L Watts,
Tod E Strohmayer
Comments: 5 pages, 5 figures using emulateapj. Accepted for publication in ApJ
Letters
The recent discovery of high frequency oscillations in giant flares from SGR
1806-20 and SGR 1900+14 may be the first direct detection of vibrations in a
neutron star crust. If this interpretation is correct it offers a novel means
of testing the neutron star equation of state, crustal breaking strain, and
magnetic field configuration. Using timing data from RHESSI, we have confirmed
the detection of a 92.5 Hz Quasi-Periodic Oscillation (QPO) in the tail of the
SGR 1806-20 giant flare. We also find another, stronger, QPO at higher
energies, at 626.5 Hz. Both QPOs are visible only at particular (but different)
rotational phases, implying an association with a specific area of the neutron
star surface or magnetosphere. At lower frequencies we confirm the detection of
an 18 Hz QPO, at the same rotational phase as the 92.5 Hz QPO, and report the
additional presence of a broad 26 Hz QPO. We are however unable to make a
robust confirmation of the presence of a 30 Hz QPO, despite higher countrates.
We discuss our results in the light of neutron star vibration models.
Title: A Deep Radio Survey of Abell 2125 III: The Cluster Core - Merging and
Stripping
Authors: F. N. Owen (NRAO),
W. C. Keel (Alabama),
Q. D. Wang (UMass),
M. J. Ledlow (Gemini),
G.E. Morrison (NOAO)
Comments: 36 pages, 16 figures, accepted AJ, paper with full resolution figures
is available at http:www.aoc.nrao.edu/~fowen/papers/a2125/a2125paper3.ps.gz
We use radio, near-IR, optical, and X-ray observations to examine dynamic
processes in the central region of Abell 2125. In addition to the central
triple, including members of both major dynamical subsystems identified from a
redshift survey, this region features a galaxy showing strong evidence for
ongoing gas stripping during a high-velocity passage through the gas in the
cluster core. The disk galaxy C153 exhibits a plume stretching toward the
cluster center seen in soft X-rays by Chandra, parts of which are also seen in
[O II] emission and near-UV continuum light. HST imaging shows a distorted
disk, with star-forming knots asymmetrically distributed and remnant spiral
structure possibly defined by dust lanes. The stars and ionized gas in its disk
are kinematically decoupled, demonstrating that pressure stripping must be
important, and that tidal disruption is not the only mechanism at work.
Comparison of the gas properties seen in the X-ray and optical data on the
plume highlight significant features of the history of stripped gas in the
intracluster medium. The nucleus of C153 also hosts an AGN, shown by the weak
and distorted extended radio emission and a radio compact core. The unusual
strength of the stripping signatures in this instance is likely related to the
high relative velocity of the galaxy with respect to the intracluster medium,
during a cluster/cluster merger, and its passage very near the core of the
cluster. Another sign of recent dynamical events is diffuse starlight
asymmetrically placed about the central triple in a cD envelope. Transient and
extreme dynamical events as seen in Abell 2125 may be important drivers of
galaxy evolution in the cores of rich clusters.
Title: Einstein's Geometrization vs. Spatial Coordinate-rescale Cancellation of
Static Gravity
Authors: Jin He
Comments: 14 pages; Note that you do not mail any comment to the affiliation.
The author may be jobless
Particle's acceleration in static homogeneous gravitational field is
cancelled by any freely-falling frame. The present paper shows that the
acceleration is also cancelled by a spatial curvilinear coordinate system. The
coordinate system is simply a spatial square-root coordinate rescale in the
field direction, no relative motion being involved. In an inhomogeneous
gravitational field, no such freely-falling frame can be found. However, the
present paper shows that spatial radial coordinate-rescales which cancel
gravity are still there for several cases of inhomogeneous static gravity. This
suggests that spacetime is flat which has inertial frame of Minkowski metric
$\eta_{ij}$. Gravity is a tensor $g_{\alpha \beta}$ on the spacetime, which is
called effective metric. The effective metric emerges from the coordinate
rescale. The gravitational field of an isolated point mass requires a radial
translational coordinate rescale. The corresponding effective metric is
different from that of Schwarzchild. To first order, its prediction on the
deflection of light and the precession of the perihelia of planetary orbits is
the same as the one of general relativity (GR). However, the metric has the
important prediction that the common angular momentum is not conserved.
Instead, the shadow angular momentum is conserved. Because the distance between
a point and its shadow is $GM/c^2$ ($\approx $ 1.5km for the mass of sun), the
test on the prediction needs high precision solar or other observations and is
left for future work.
Until recently, X-ray flares during the afterglow of gamma ray bursts (GRBs)
were a rarely detected phenomenon, thus their nature is unclear. During the
afterglow of GRB 050502B, the largest X-ray flare ever recorded rose rapidly
above the afterglow lightcurve detected by the Swift X-ray Telescope. The peak
flux of the flare was >500 times that of the underlying afterglow, and it
occurred at >12 minutes after the nominal prompt burst emission. The fluence of
this X-ray flare, (1.0 +/- 0.05) x 10^{-6} erg cm^{-2} in the 0.2-10.0 keV
energy band, exceeded the fluence of the nominal prompt burst. The spectra
during the flare were significantly harder than those measured before and after
the flare. Later in time, there were additional flux increases detected above
the underlying afterglow, as well as a break in the afterglow lightcurve. All
evidence presented below, including spectral and particularly timing
information during and around the giant flare, suggests that this giant flare
was the result of internal dissipation of energy due to late central engine
activity, rather than an afterglow-related effect. We also find that the data
are consistent with a second central engine activity episode, in which the
ejecta is moving slower than that of the initial episode, causing the giant
flare and then proceeding to overtake and refresh the afterglow shock, thus
causing additional activity at even later times in the lightcurve.
In this work we present a sensitive and systematic single-dish survey of CCS
emission (complemented with ammonia observations) at 1 cm, toward a sample of
low- and intermediate-mass young star forming regions known to harbor water
maser emission, made with NASA's 70 m antenna at Robledo de Chavela, Spain.
Out of the 40 star forming regions surveyed in the CCS(2_{1}-1_{0}) line,
only 6 low-mass sources show CCS emission: one transitional object between
pre-stellar and protostellar Class 0 phase (GF9-2), three Class 0 protostars
(L1448-IRS3, L1448C, and B1-IRS), a Class I source (L1251A), and a young T
Tauri star (NGC2071-North). Since CCS is considered an ``early-time'' (<10E+5
yr) molecule, we explain these results by either proposing a revision of the
classification of the age of NGC2071-North and L1251A, or suggesting the
possibility that the particular physical conditions and processes of each
source affect the destruction/production of the CCS. No statistically
significant relationship was found between the presence of CCS and parameters
of the molecular outflows and their driving sources. Nevertheless, we found a
significant relationship between the detectability of CCS and the ammonia peak
intensity (higher in regions with CCS), but not with its integrated intensity.
This tendency found may suggest that the narrower ammonia line widths in the
less turbulent medium associated with younger cores may compensate for the
differences in ammonia peak intensity, rendering differences in integrated
intensity negligible. From the CCS detection rate we derive a lifetime of this
molecule of ~(0.7-3) x 10E+4 yr in low-mass star forming regions.
HH 110 and HH 262 are two Herbig-Haro jets with rather peculiar, chaotic
morphology. In the two cases, no source suitable to power the jet has been
detected along the outflow, at optical or radio wavelengths. Both, previous
data and theoretical models, suggest that these objects are tracing an early
stage of an HH jet/dense cloud interaction. We present the first results of the
integral field spectroscopy observations made with the PMAS spectrophotometer
(with the PPAK configuration) of these two turbulent jets. New data of the
kinematics in several characteristic HH emission lines are shown. In addition,
line-ratio maps have been made, suitable to explore the spatial excitation an
density conditions of the jets as a function of their kinematics.
Mid-infrared observations of Active Galactic Nuclei (AGN) are important for
understanding of the physical conditions around the central accretion engines.
Chandra and XMM-Newton X-ray observations of a 300 arcmin^2 region in the
Extended Groth Strip are used to select a sample of~150 AGN. The Spitzer
instruments IRAC and MIPS detect 68-80% of these sources, which show a wide
range of mid-infrared properties. About 40% of the sources have red power-law
spectral energy distributions (f_nu ~ nu^alpha, alpha<0) in the 3.6-8 um IRAC
bands. In these sources the central engine dominates the emission at both X-ray
and IR wavelengths. Another 40% of the sources have blue mid-IR spectral energy
distributions (alpha>0) with their infrared emission dominated by the host
galaxy; the remaining 20% are not well-fit by a power law. Published IRAC color
criteria for AGN select most of the red sources, but only some of the blue
sources. As with all other known methods, selecting AGN with mid-IR colors will
not produce a sample that is simultaneously complete and reliable. The IRAC SED
type does not directly correspond to X-ray spectral type (hard/soft). The
mid-IR properties of X-ray-detected Lyman-break, radio, submillimeter, and
optically-faint sources vary widely and, for the most part, are not distinct
from those of the general X-ray/infrared source population. X-ray sources emit
6-11% of the integrated mid--IR light, making them significant contributors to
the cosmic infrared background.
We have carried out a spectroscopic survey of several B, Be, and shell stars
in optical and near-infrared regions. Line profiles of the H-alpha line and of
selected Fe II and O I lines are presented.
Title: Assisted stellar suicide in V617 Sgr
Authors: J. E. Steiner (IAG-USP),
A. S. Oliveira (SOAR Telescope),
D. Cieslinski (INPE),
T. V. Ricci (IAG-USP)
Comments: 4 pages, accepted for publication in A&A Letters
V617 Sgr is a V Sagittae star - a group of binaries thought to be the
galactic counterparts of the Compact Binary Supersoft X-ray Sources - CBSS. To
check this hypothesis, we measured the time derivative of its orbital period.
Observed timings of eclipse minima spanning over 30,000 orbital cycles are
presented. We found that the orbital period evolves quite rapidly: P/Pdot = 1.1
x 10^{6} years. This is consistent with the idea that V617 Sgr is a wind driven
accretion supersoft source. As the binary system evolves with a time-scale of
about one million years, which is extremely short for a low mass evolved
binary, it is likely that the system will soon end either by having its
secondary completely evaporated or by the primary exploding as a supernova of
type Ia.
Title: Astrometric Monitoring of Stellar Orbits at the Galactic Center with a
Next Generation Large Telescope
Authors: Nevin N. Weinberg (1, 2),
Milos Milosavljevic (1),
Andrea M. Ghez (3) ((1) Caltech, (2) KITP, (3) UCLA)
Comments: 8 pages, 3 figures. ASP Conf. Series "Astrometry in the Age of the
Next Generation of Large Telescopes", 2005, v.338, eds. P. Kenneth Seidelmann
and Alice K. B. Monet
Journal-ref: ASP Conf. Proc. 338 (2005) 252
We show that with a Next Generation Large Telescope one can detect the
accelerated motions of ~100 stars orbiting the massive black hole at the
Galactic center. The positions and velocities of these stars will be measured
to astrometric and spectroscopic precision several times better than currently
attainable enabling detailed measurements of the gravitational potential in the
neighborhood of the massive black hole. We show that the monitoring of stellar
motions with such a telescopes enables: (1) a measurement of the Galactic
center distance R_0 to better than 0.1% accuracy, (2) a measurement of the
extended matter distribution near the black hole, including that of the exotic
dark matter, (3) a detection of general relativistic effects due to the black
hole including the prograde precession of stars and possibly the black hole
spin, and (4) a detection of gravitational encounters between monitored stars
and stellar remnants that accumulate near the Galactic center. Such encounters
probe the mass function of the remnants.
Title: "Expansion" around the vacuum: how far can we go from Lambda?
Authors: J.S. Alcaniz,
H. Stefancic
Comments: 7 pages, 3 figures, LaTeX
The cosmological constant ($\Lambda$), i.e., the energy density stored in the
true vacuum state of all existing fields in the Universe, is the simplest and
the most natural possibility to describe the current cosmic acceleration.
However, despite its observational successes, such a possibility exacerbates
the well known $\Lambda$ problem, requiring a natural explanation for its
small, but nonzero, value. In this paper we discuss how different our Universe
may be from the $\Lambda$CDM model by studying observational aspects of a kind
of "expansion" around the vacuum given by the equation of (EOS)
$p_{d}=-\rho_{d} - A \rho_{d}^{\alpha}$. In different parameter regimes such a
parametrization is capable of describing both quintessence-like and phantom
like dark energy, transient acceleration, and various (non)singular
possibilities for the final destiny of the Universe, including singularities at
finite values of the scale factor, the so-called "Big Rip", as well as sudden
future singularities. By using some of the most recent cosmological
observations we show that if the functional form of the dark energy EOS has
additional parameters very little can be said about their values from the
current observational results, which postpones, until the arrival of more
precise observational data, a definitive answer to the question posed above.
We present a spectroscopic survey using the MMT/Hectospec fiber spectrograph
of 24 micron sources selected with the Spitzer Space Telescope in the Spitzer
First Look Survey. We report 1295 new redshifts for 24 micron sources,
including 598 with f(24um) > 1 mJy. Combined with 291 additional redshifts for
sources from the Sloan Digital Sky Survey (SDSS) our observing program was
highly efficient and is ~90% complete for i < 21 mag and f(24um) > 1 mJy, and
is 37% complete for i < 20.5 mag and 0.3 mJy < f(24um) < 1 mJy. Our Hectospec
survey includes 1065 and 176 objects spectroscopically classified as galaxies
and QSOs, respectively. Combining the Hectospec and SDSS samples, we find
galaxies to z(gal) < 0.98 and QSOs to z(QSO) < 3.6, with mean redshifts of
<z(gal)>=0.27 and <z(QSO)>=1.1. As part of this paper, we publish the redshift
catalogs and the reduced spectra.
Title: X-ray flare modeling in the single giant HR 9024
Authors: Paola Testa (MIT),
David Garcia-Alvarez (SAO),
Fabio Reale (Univ. Palermo),
David Huenemoerder (MIT)
Comments: 2 pages, 4 figures. To be included in the proceedings of the 'X-ray
universe 2005 meeting' held in San Lorenzo de El Escorial (Spain), 26-30 Sep
2005
We analyze a Chandra-HETGS observation of the single G-type giant HR 9024.
The high flux allows us to examine spectral line and continuum diagnostics at
high temporal resolution, to derive plasma parameters (thermal distribution,
abundances, temperature, ...). A time-dependent 1D hydrodynamic loop model with
semi-length 10$^{12}$cm ($\sim R_{\star}$), and impulsive footpoint heating
triggering the flare, satisfactorily reproduces the observed evolution of
temperature and emission measure, derived from the analysis of the strong
continuum emission. The observed characteristics of the flare appear to be
common features in very large flares in active stars (also pre-main sequence
stars), possibly indicating some fundamental physics for these very dynamic and
extreme phenomena in stellar coronae.
We have performed monitoring observations of the flux density toward the
Galactic center compact radio source, Sagittarius A* (Sgr A*), which is a
supermassive black hole, from 1996 to 2005 using the Nobeyama Millimeter Array
of the Nobeyama Radio Observatory, Japan. These monitoring observations of Sgr
A* were carried out in the 3- and 2-mm (100 and 140 GHz) bands, and we have
detected several flares of Sgr A*. We found intraday variation of Sgr A* in the
2000 March flare. The twofold increase timescale is estimated to be about 1.5
hr at 140 GHz. This intraday variability suggests that the physical size of the
flare-emitting region is compact on a scale at or below about 12 AU (~150 Rs;
Schwarzschild radius). On the other hand, clear evidence of long-term periodic
variability was not found from a periodicity analysis of our current millimeter
data set.
Title: The early reionization with the primordial magnetic fields
Authors: Hiroyuki Tashiro,
Naoshi Sugiyama
Comments: 8 pages, 5 figures. Submitted to MNRAS
The early reionization of the intergalactic medium, which is favored from the
WMAP temperature-polarization cross-correlations, contests the validity of the
standard scenario of structure formation in the cold dark matter cosmogony. It
is difficult to achieve early enough star formation without rather extreme
assumptions such as very high escape fraction of ionizing photons from
proto-galaxies or a top-heavy initial mass function. Here we propose an
alternative scenario that is additional fluctuations on small scales induced by
primordial magnetic fields trigger the early structure formation. We found that
ionizing photons from Population III stars formed in dark haloes can easily
reionize the universe by $z \simeq 15$ if the strength of primordial magnetic
fields is larger than $0.6 \times 10^{-9}$Gauss.
We report the detection of hard X-ray emission from the field of the
star-forming region NGC 6334 with the the International Gamma-Ray Astrophysics
Laboratory INTEGRAL. The JEM-X monitor and ISGRI imager aboard INTEGRAL and
Chandra ACIS imager were used to construct 3-80 keV images and spectra of NGC
6334. The 3-10 keV and 10-35 keV images made with JEM-X show a complex
structure of extended emission from NGC 6334. The ISGRI source detected in the
energy ranges 20-40 keV and 40-80 keV coincides with the NGC 6334 ridge. The
20-60 keV flux from the source is (1.8+-0.37)*10(-11) erg cm(-2) s(-1).
Spectral analysis of the source revealed a hard power-law component with a
photon index about 1. The observed X-ray fluxes are in agreement with
extrapolations of X-ray imaging observations of NGC 6334 by Chandra ACIS and
ASCA GIS. The X-ray data are consistent with two very different physical
models. A probable scenario is emission from a heavily absorbed, compact and
hard Chandra source that is associated with the AGN candidate radio source NGC
6334B. Another possible model is the extended Chandra source of nonthermal
emission from NGC 6334 that can also account for the hard X-ray emission
observed by INTEGRAL. The origin of the emission in this scenario is due to
electron acceleration in energetic outflows from massive early type stars. The
possibility of emission from a young supernova remnant, as suggested by earlier
infrared observations of NGC 6334, is constrained by the non-detection of 44Ti
lines.
We report on a multiwavelength campaign on the TeV gamma-ray blazar Markarian
(Mrk) 421 performed during December 2002 and January 2003. These target of
opportunity observations were initiated by the detection of X-ray and TeV
gamma-ray flares with the All Sky Monitor (ASM) on board the Rossi X-ray Timing
Explorer (RXTE) and the 10~m Whipple gamma-ray telescope.The campaign included
observational coverage in the radio (University of Michigan Radio Astronomy
Observatory), optical (Boltwood, La Palma KVA 0.6m, WIYN 0.9m), X-ray (RXTE
pointed telescopes), and TeV gamma-ray (Whipple and HEGRA) bands.
At TeV energies, the observations revealed several flares at intermediate
flux levels, peaking between 1 and 1.5 times the flux from the Crab Nebula.
While the time averaged spectrum can be fitted with a single power law of
photon index Gamma =2.8, we find some evidence for spectral variability.
Confirming earlier results, the campaign reveals a rather loose correlation
between the X-ray and TeV gamma-ray fluxes. In one case, a very strong X-ray
flare is not accompanied by a comparable TeV gamma-ray flare. Although the
source flux was variable in the optical and radio bands, the sparse sampling of
the optical and radio light curves does not allow us to study the correlation
properties in detail.
We present a simple analysis of the data with a synchrotron-self Compton
model, emphasizing that models with very high Doppler factors and low magnetic
fields can describe the data.
Title: Nonlinear Criterion for the Stability of Molecular Clouds
Authors: Ruben Krasnopolsky,
Charles F. Gammie
Comments: 11 pages, 5 figures
Journal-ref: Astrophys.J. 635 (2005) 1126-1135
Dynamically significant magnetic fields are routinely observed in molecular
clouds, with mass-to-flux ratio lambda = (2 pi sqrt{G}) (Sigma/B) ~ 1 (here
Sigma is the total column density and B is the field strength). It is widely
believed that ``subcritical'' clouds with lambda < 1 cannot collapse, based on
virial arguments by Mestel and Spitzer and a linear stability analysis by
Nakano and Nakamura. Here we confirm, using high resolution numerical models
that begin with a strongly supersonic velocity dispersion, that this criterion
is a fully nonlinear stability condition. All the high-resolution models with
lambda <= 0.95 form ``Spitzer sheets'' but collapse no further. All models with
lambda >= 1.02 collapse to the maximum numerically resolvable density. We also
investigate other factors determining the collapse time for supercritical
models. We show that there is a strong stochastic element in the collapse time:
models that differ only in details of their initial conditions can have
collapse times that vary by as much as a factor of 3. The collapse time cannot
be determined from just the velocity dispersion; it depends also on its
distribution. Finally, we discuss the astrophysical implications of our
results.
Title: Detection with RHESSI of high frequency X-ray oscillations in the tail
of the 2004 hyperflare from SGR 1806-20
Authors: Anna L Watts,
Tod E Strohmayer
Comments: 5 pages, 5 figures using emulateapj. Accepted for publication in ApJ
Letters
The recent discovery of high frequency oscillations in giant flares from SGR
1806-20 and SGR 1900+14 may be the first direct detection of vibrations in a
neutron star crust. If this interpretation is correct it offers a novel means
of testing the neutron star equation of state, crustal breaking strain, and
magnetic field configuration. Using timing data from RHESSI, we have confirmed
the detection of a 92.5 Hz Quasi-Periodic Oscillation (QPO) in the tail of the
SGR 1806-20 giant flare. We also find another, stronger, QPO at higher
energies, at 626.5 Hz. Both QPOs are visible only at particular (but different)
rotational phases, implying an association with a specific area of the neutron
star surface or magnetosphere. At lower frequencies we confirm the detection of
an 18 Hz QPO, at the same rotational phase as the 92.5 Hz QPO, and report the
additional presence of a broad 26 Hz QPO. We are however unable to make a
robust confirmation of the presence of a 30 Hz QPO, despite higher countrates.
We discuss our results in the light of neutron star vibration models.