title: Thermal Instability in Clusters of Galaxies with Conduction

abstract:
  We consider a model of galaxy clusters in which the hot gas is in hydrostatic
equilibrium and maintains energy balance between radiative cooling and heating
by thermal conduction. We analyze the thermal stability of the gas using a
Lagrangian perturbation analysis. For thermal conductivity at the level of
20-40 % of Spitzer conductivity, consistent with previous estimates for cluster
gas, we find that the growth rate of the most unstable global radial mode is ~
6-9 times lower than the growth rate of local isobaric modes at the cluster
center in the absence of conduction. The growth time in typical clusters is ~
2-5 Gyr, which is comparable to the time since the last major merger episode,
when the gas was presumably well mixed. Thus, we suggest that thermal
instability is not dynamically significant in clusters, provided there is an
adequate level of thermal conduction. On the other hand, if the heating of the
gas is not the result of thermal conduction or any other diffusive process such
as turbulent mixing, then the thermal instability has a growth time under a Gyr
in the central regions of the cluster and is a serious threat to equilibrium.
We also analyze local nonradial modes and show that the Lagrangian technique
leads to the same dispersion relation as the Eulerian approach, provided that
clusters are initially in strict thermal equilibrium. Because cluster gas is
convectively stable, nonradial modes always have a smaller growth rate than
equivalent radial modes.


title: Cosmic Reionisation by Stellar Sources: Population II Stars

abstract:
  We study the reionisation of the Universe by stellar sources using a
numerical approach that combines fast 3D radiative transfer calculations with
high resolution hydrodynamical simulations. Ionising fluxes for the sources are
derived from intrinsic star formation rates computed in the underlying
hydrodynamical simulations. Our mass resolution limit for sources is M~ 4.0 x
10^7 h^-1 M_sol, which is roughly an order of magnitude smaller than in
previous studies of this kind. Our calculations reveal that the reionisation
process is sensitive to the inclusion of dim sources with masses below ~10^9
h^-1 M_sol. We present the results of our reionisation simulation assuming a
range of escape fractions for ionising photons and make statistical comparisons
with observational constraints on the neutral fraction of hydrogen at z~6
derived from the z=6.28 SDSS quasar of Becker and coworkers. Our best fitting
model has an escape fraction of ~20% and causes reionisation to occur by z~8,
although the IGM remains fairly opaque until z~6. In order to simultaneously
match the observations from the z=6.28 SDSS quasar and the optical depth
measurement from WMAP with the sources modeled here, we require an evolving
escape fraction that rises from f_esc=0.20 near z~6 to f_esc>~10 at z~18.


title: Interstellar extinction in the direction of the Aquila Rift

abstract:
  The distance dependence of interstellar extinction in the direction of the
Aquila Rift is investigated using 473 stars observed in the Vilnius photometric
system. Front edge of the dark clouds in the area is found to be at 225$\pm$55
pc and the thickness of the cloud system can be about 80 pc. The maximum
extinction A_V in the clouds is close to 3.0 mag. Two stars with larger
extinction are found and discussed. Since the new distance of the clouds is
larger than the previously accepted distance, the cloud system mass should be
increased up to 2.7 10^5 M_sun which is close to the virial mass estimated from
the CO velocity dispersion. Additional arguments are given in favor of the
genetic relation between the Serpens and the Scorpio-Ophiuchus dark clouds.


title: Bulge Microlensing Optical Depth from EROS 2 observations

abstract:
  We present a measurement of the microlensing optical depth toward the
Galactic bulge based on the analysis of 15 contiguous1 square degrees fields
centered on (l=2.5 deg, b=-4.0 deg) and containing 1.42 million clump-giant
stars (belonging to the extended clump area) monitored during almost three
bulge seasons by EROS (Experience de Recherche d'Objets Sombres). We find a
microlensing optical depth towards the bulge tau_bulge=0.94 +/- 0.29 10^-6
averaged over all fields, based on 16 microlensing events with clump giants as
sources. This value is substantially below several other determinations by the
MACHO and OGLE groups and is more in agreement with what is expected from
axisymmetric and non-axisymmetric bulge models.


title: The Cepheid Distance to NGC 5236 (M 83) with the VLT

abstract:
  Cepheids have been observed in NGC 5236 (M 83) using the ANTU (UT1) 8.2 meter
telescope of the ESO VLT with FORS1. Observations over 34 epochs in V and I
have been made between January 2000 and July 2001. Twelve Cepheid candidates
have periods between 12 and 55 days. The true distance modulus is adopted to be
(m-M)_0 = 28.25 +/- 0.15, which corresponds to a distance of 4.5 +/- 0.3 Mpc.
The distance of NGC 5253 has been rediscussed. The mean distance of (m-M)_0 =
28.01 +/- 0.15 (based on SN 1972E) shows the galaxy to be a close neighbor of M
83 (separation = 0.5 +/- 0.4 Mpc), suggesting that the two galaxies may have
interacted in the past and thus possibly explaining the amorphous morphology of
NGC 5253.
  M 83 is the principal member of the nearby M 83 group containing also,
besides NGC 5253, several dwarf members, for five of which TRGB distances are
available (Karachentsev et al. 2002a, A&A, 385, 21). The adopted group distance
of (m-M)_0 = 28.28 +/- 0.10 (4.5 +/- 0.2 Mpc) together with its mean recession
velocity of v_LG = 249 +/- 42 km/s shows again the extreme quietness of the
local (1 Mpc to 10 Mpc) expansion field. M 83 fits onto the local mean Hubble
flow line of the velocity-distance relation (with H_0 ~ 60) with no significant
deviation, supporting the earlier conclusion that the local velocity expansion
field is remarkably cold on a scale of 10 Mpc, contrary to the predictions of
the simplest cold dark matter model for large scale structure. The role of a
cosmological constant has been invoked as a possible solution in providing a
nearly uniform force field everywhere in the presence of a lumpy galaxy
distribution. (abridged)


title: The Multi-phase Absorption Systems Toward PG 1206+459

abstract:
  A high-resolution HST/STIS spectrum (R=30,000) is presented of the three
MgII-selected absorption systems (A, B, and C, clustered within 1500km/s) at
z~0.93 toward the quasar PG 1206+459. A WIYN Gunn i-band image of the quasar
field and spectroscopy of two galaxy candidates are also presented. A
multi-phase medium is seen in all three systems, consistent with smaller,
denser clouds producing low-ionization transitions (MgII, FeII, and SiII) and
larger, diffuse clouds giving rise to high-ionization transitions (CIV, NV,
and/or OVI). (1) System A, a multi-cloud, weak MgII absorber at z=0.9254,
requires a super-solar metallicity in both low- and high-ionization phases,
unless an alpha-group enhancement is included. With the unusually complex
velocity structure resolved in the NV profiles, this system is unlikely to
represent a traditional galaxy disk/corona. The most likely candidate host
galaxy is a ~2L^*, apparently warped, spiral at an impact parameter of 43h^-1
kpc. (2) System B, at z=0.9276, has the strongest MgII absorption and has an
approximately solar metallicity in the low-ionization phase. The smooth, broad
high-ionization profiles may indicate a coronal structure similar to that of
the Milky Way. The redshift of an L^* galaxy (z=0.9289), at an impact parameter
of 38h^-1 kpc is consistent with the redshift of this system. (3) System C, at
z=0.9342, has a single component in MgII, separated from the other two systems
by ~1000km/s. It lacks the small, low-ionization cloud characteristic of an
isolated single-cloud, weak MgII absorber. Its absorption properties are
similar to the ``satellite clouds'' of classic strong MgII absorbers, so this
could be a high-velocity cloud in the galaxy group responsible for the systems,
possibly related to a 0.2L^* galaxy at an impact parameter of 43h^-1 kpc.


title:
Spectral Properties of Compressible Magnetohydrodynamic Turbulence from
  Numerical Simulations

abstract:
  We analyze the spectral properties of driven, supersonic compressible
magnetohydrodynamic (MHD) turbulence obtained via high-resolution numerical
experiments, for application to understanding the dynamics of giant molecular
clouds. Via angle-averaged power spectra, we characterize the transfer of
energy from the intermediate, driving scales down to smaller dissipative
scales, and also present evidence for inverse cascades that achieve
modal-equipartition levels on larger spatial scales. Investigating compressive
versus shear modes separately, we evaluate their relative total power, and find
that as the magnetic field strength decreases, (1) the shear fraction of the
total kinetic power decreases, and (2) slopes of power-law fits over the
inertial range steepen. To relate to previous work on incompressible MHD
turbulence, we present qualitative and quantitative measures of the
scale-dependent spectral anisotropy arising from the shear-Alfv\'{e}n cascade,
and show how these vary with changing mean magnetic field strength. Finally, we
propose a method for using anisotropy in velocity centroid maps as a diagnostic
of the mean magnetic field strength in observed cloud cores.


title: XAssist: A System for the Automation of X-ray Astrophysics Analysis

abstract:
  XAssist is a NASA AISR-funded project for the automation of X-ray
astrophysics, with emphasis on galaxies. It is nearing completion of its
initially funded effort, and is working well for Chandra and ROSAT HRI data.
Initial support for XMM-Newton data is present as well. It is capable of data
reprocessing, source detection, and preliminary spatial, temporal and spectral
analysis for each source with sufficient counts. The bulk of the system is
written in Python, which in turn drives underlying software (CIAO for Chandra
data, etc.). Future work will include a GUI (mainly for beginners and status
monitoring) and the exposure of at least some functionality as web services.
The latter will help XAssist to eventually become part of the VO, making
advanced queries possible, such as determining the X-ray fluxes of counterparts
to HST or SDSS sources (including the use of unpublished X-ray data), and add
the ability of ``on-the-fly'' X-ray processing. Pipelines are running on ROSAT,
Chandra and now XMM-Newton observations of galaxies to demonstrate XAssist's
capabilities, and the results are available online (in real time) at
http://www.xassist.org . XAssist itself as well as various associated projects
are available for download.


title:
Unification to the "Pseudo-General-Relativistic" analysis of accretion
  disks around rotating black holes and neutron stars

abstract:
  I analyse the relativistic accretion phenomena around rotating black holes
and neutron stars in pseudo-Newtonian approach and show both the kinds of disk
can be treated in an unified manner. For this purpose, number of
pseudo-Newtonian potentials are in literature, applicable to describe the
relativistic properties of accretion disk. While, Kerr metric is used to
describe the pseudo-Newtonian potential for accretion disk around black hole,
the Hartle-Thorne metric is considered to describe disk around neutron star.
Two other potentials were proposed to describe the temporal effects of the
accretion disk. Using these potentials, I study the global parameter space of
the accretion disk around black holes and neutron stars. I show that, for
different angular momenta of the compact object, the valid disk parameter
region dramatically changes and disk may become unstable in certain situations.
To bring it in the stable situation, the angular momentum of the accreting
matter has to be reduced/enhanced (for co/counter-rotating disk) by means of
some physical process. I also study, how the fluid properties get changed with
different rotations of the compact objects. Moreover, I show the effect of
viscosity to the fluid properties of the disk. Thus, I find out the unified
physical parameter regime, for which the stable accretion disk can be formed.
Subsequently, a theoretical prediction of kHz QPO is given, for a fast rotating
compact object as 4U 1636-53.


title: A Systematic Study Of X-Ray Variability In The ROSAT All-Sky Survey

abstract:
  We present a systematic search for variability among the ROSAT All-Sky Survey
(RASS) X-ray sources. We generated lightcurves for about 30000 X-ray point
sources detected sufficiently high above background. For our variability study
different search algorithms were developed in order to recognize flares,
periods and trends, respectively. The variable X-ray sources were optically
identified with counterparts in the SIMBAD, the USNO-A2.0 and NED data bases,
but a significant part of the X-ray sources remains without cataloged optical
counterparts. Out of the 1207 sources classified as variable 767 (63.5 %) were
identified with stars, 118 (9.8 %) are of extragalactic origin, 10 (0.8 %) are
identified with other sources and 312 (25.8 %) could not uniquely be identified
with entries in optical catalogs. We give a statistical analysis of the
variable X-ray population and present some outstanding examples of X-ray
variability detected in the ROSAT all-sky survey. Most prominent among these
sources are white dwarfs, apparently single, yet nevertheless showing periodic
variability. Many flares from hitherto unrecognised flare stars have been
detected as well as long term variability in the BL Lac 1E1757.7+7034.


title: Synchrotron-Self Compton Spectral Evolution of PKS 2155-304

abstract:
  The high frequency peaked blazar PKS 2155-304 is one of the brightest and
most intensively studied prototype of BL Lac objects. Gamma-rays from PKS
2155-304 have been detected from the MeV to TeV ranges. We computed a
synchrotron self-Compton (SSC) model, based on the temporal behavior of the
particles distribution, responsible for the high-energy emission. Using the
available simultaneous multiwavelength data, we simulated the overall spectral
energy distribution (SED) and the spectral variability of this source.


title: Cosmic Microwave Radiation Anisotropies in Brane Worlds

abstract:
  We propose a new formulation to calculate the Cosmic Microwave Background
(CMB) spectrum in the Randall Sundrum two-branes model based on recent
progresses in solving the bulk geometry using a low energy approximation. The
evolution of the anisotropic stress imprinted on the brane by the 5D Weyl
tensor is calculated. An impact of the dark radiation perturbation on CMB
spectrum is investigated in a simple model assuming an initially
scale-invariant adiabatic perturbations. The dark radiation perturbation
induces isocurvature perturbations, but the resultant spectrum can be quite
different from the prediction of simple mixtures of adiabatic and isocurvature
perturbations due to Weyl anisotropic stress.


title:
Peculiar Features of the Velocity Field of OB Associations and the
  Spiral Structure of the Galaxy

abstract:
  Some of the peculiar features of the periodic velocity-field structure for OB
associations can be explained by using the model of Roberts and Hausman (1984),
in which the behavior of a system of dense clouds is considered in a perturbed
potential. The absence of statistically significant variations in the azimuthal
velocity across the Carina arm, probably, results from its sharp increase
behind the shock front, which is easily blurred by distance errors. The
existence of a shock wave in the spiral arms and, at the same time, the
virtually free motion of OB associations in epicycles can be reconciled in the
model of particle clouds with a mean free path of 0.2-2 kpc. The velocity field
of OB associations exhibits two appreciable nonrandom deviations from an ideal
spiral pattern: a 0.5-kpc displacement of the Cygnus- and Carina-arm fragments
from one another and a weakening of the Perseus arm in quadrant III. However,
the identified fragments of the Carina, Cygnus, and Perseus arms do not belong
to any of the known types of spurs.


title:
The unusual supernova remnant surrounding the ultraluminous X-ray source
  IC 342 X-1

abstract:
  We report the results of an observation of a large diameter (110 pc)
supernova remnant (SNR) found to encircle the position of the ultraluminous
X-ray source (ULX) IC 342 X-1. The inferred initial energy input to the SNR is
at least 2 -- 3 times greater than the canonical energy for an ``ordinary''
supernova remnant. Two regions on the inside of the shell are bright in [O III]
lambda5007 emission, possibly as the result of X-ray photoionization by the
ULX. If this is the case, then the morphology of this nebulosity implies that
the X-ray emission from the ULX is anisotropic. The presence of the ULX, most
probably a black hole X-ray binary, within an unusually energetic supernova
remnant suggests that we may be observing the aftermath of a gamma-ray burst,
though other origins for the energetic nebula are discussed.


title: The high-velocity outflow in the proto-planetary nebula Hen 3-1475

abstract:
  The proto-planetary nebula Hen 3-1475 shows a remarkable highly collimated
optical jet with an S-shaped string of three pairs of knots and extremely high
velocities. We present here a detailed analysis of the overall morphology,
kinematic structure and the excitation conditions of these knots based on deep
ground-based high dispersion spectroscopy complemented with high spatial
resolution spectroscopy obtained with STIS onboard HST, and WFPC2 [N II]
images. The spectra obtained show double-peaked, extremely wide emission line
profiles, and a decrease of the radial velocities with distance to the source
in a step-like fashion. We find that the emission line ratios observed in the
intermediate knots are consistent with a spectrum arising from the
recombination region of a shock wave with shock velocities ranging from 100 to
150 km/s. We propose that the ejection velocity is varying as a function of
time with a quasi-periodic variability (with timescale of the order of 100
years) and the direction of ejection is also varying with a precession period
of the order of 1500 years.


title: Cluster Formation Rate in Models with Dark Energy

abstract:
  Based on flat Friedmann-Robertson Walker cold dark matter (CDM) type models
driven by non-relativistic matter and an exotic fluid (quintessence) with an
equation of state: $p_{Q}=w\rho_{Q}$ ($-1\le w<0$), we investigate whether or
not the large scale dynamical effects regarding the cluster formation and
virialization are related to the cosmic equation of state. Using the non-linear
spherical collapse we find that the cluster formation rate, in quintessence
models, is intermediate between the open and $\Lambda$CDM respectively. For the
QCDM case, using the virial theorem and energy conservation and assuming a
spherical mass overdensity shell, we obtain analytically the ratio between the
final (virial) and the turn-around radius. We find that the above ratio is
almost independent from the equation of state.


title: Kuiper-belt Binary Formation through Exchange Reactions

abstract:
  Recent observations (Burnes et al 2002,Veillet et al 2002, Margot et al
2002a) have revealed an unexpectedly high binary fraction among the
Trans-Neptunian Objects (TNOs) that populate the Kuiper Belt. The TNO binaries
are strikingly different from asteroid binaries in four respects (Veillet et al
2002): their frequency is an order of magnitude larger, the mass ratio of their
components is closer to unity, and their orbits are wider and highly eccentric.
Two explanations have been proposed for their formation, one assuming large
numbers of massive bodies (Weidenschilling 2002), and one assuming large
numbers of light bodies (Goldreich et al 2002). We argue that both assumptions
are unwarranted, and we show how TNO binaries can be produced from a modest
number of intermediate-mass bodies of the type predicted by the gravitational
instability theory for the formation of planetesimals (Goldreich and Ward
1973). We start with a TNO binary population similar to the asteroid binary
population, but subsequently modified by three-body exchange reactions, a
process that is far more efficient in the Kuiper belt, because of the much
smaller tidal perturbations by the Sun. Our mechanism can naturally account for
all four characteristics that distinguish TNO binaries from main-belt asteroid
binaries.


title:
SCUBA Observations of Dust around Lindroos Stars: Evidence for a
  Substantial Submillimetre Disc Population

abstract:
  We have observed 22 Lindroos stars with SCUBA on the JCMT to search for
evidence of dust discs. Stars in this sample are the less massive companions of
B-type primaries and have ages of 10-170Myr. Dust was detected around three of
these stars (HD74067, HD112412 and HD99803B). The emission around HD74067 is
centrally peaked and is approximately symmetrically distributed out to ~70".
This emission either arises from a two component disc, one circumstellar and
the other circumbinary with dust masses of 0.3 and >27Mearth respectively, or
an unrelated background object. The other two detections we attribute to
circumsecondary discs with masses of 0.04 and 0.3Mearth; a circumprimary disc
is also present around HD112413 with a similar mass to that around the
companion HD112412. Cross-correlation of our sample with the IRAS catalogs only
showed evidence for dust emission at 25um and 60um toward one star (HD1438);
none of the sub-mm detections were evident in the far-IR data implying that
these discs are cold (<40K assuming beta=1). Our sub-mm detections are some of
the first of dust discs surrounding evolved stars that were not detected by
IRAS or ISO and imply that 9-14% of stars could harbour previously undetected
dust discs that await discovery in unbiased sub-mm surveys. If these discs are
protoplanetary remnants, rather than secondary debris discs, dust lifetime
arguments show that they must be devoid of small <0.1mm grains. Thus it may be
possible to determine the origin of these discs from their spectral energy
distributions. The low dust masses for this sample support the picture that
protoplanetary dust discs are depleted to the levels of the brightest debris
discs (~1Mearth) within 10Myr.


title: The X-ray background and the deep X-ray surveys

abstract:
  The deep X-ray surveys performed by the two major X-ray observatories on
flight, Chandra and XMM, are being resolving the bulk of the cosmic X-ray
background (XRB) in the 2-10 keV energy band, where the sky flux is dominated
by extragalactic emission. Although the actual fraction depends on the absolute
sky flux, which is measured with an uncertainty of ~40%, most of the XRB is
already resolved. Optical identifications of the X-ray sources in the deep
surveys are being showing that these are mainly AGN, most of which being
obscured as predicted by population synthesis models. However, first results
indicate that the redshift distribution of the sources making the XRB seems to
peak at much lower redshift than predicted by the models. In this article I
will briefly review and discuss the measurements of the XRB spectrum and the
AGN synthesis models of the XRB. Then, I will introduce the Chandra and XMM
deep X-ray surveys, mainly focusing on the Chandra Deep Field North and South.
Finally, the properties of the X-ray sources populating the deep surveys will
be described and compared with the predictions of the most recent synthesis
models.


title:
The Radio/Mid-Infrared Correlation and the Contribution of 15-micron
  Galaxies to the 1.4-GHz Source Counts

abstract:
  The radio counterparts to the 15-micron sources in the European Large Area
ISO Survey southern fields are identified in 1.4-GHz maps down to about 80
microJy. The radio-MIR correlation is investigated and derived for the first
time at these flux densities for a sample of this size. Our results show that
radio and MIR luminosities correlate almost as well as radio and FIR, at least
up to z ~ 0.6. Using the derived relation and its spread together with the
observed 15-micron counts, we have estimated the expected contribution of the
15-micron extragalactic populations to the radio source counts and the role of
MIR starburst galaxies in the well known 1.4-GHz source excess observed at
sub-mJy levels. Our analysis demonstrates that IR emitting starburst galaxies
do not contribute significantly to the 1.4-GHz counts for strong sources, but
start to become a significant fraction of the radio source population at flux
densities < 0.5 - 0.8 mJy. They are expected to be responsible for more than
60% of the observed radio counts at < 0.05 mJy. These results are in agreement
with the existing results on optical identifications of faint radio sources.


title:
Warm molecular gas, dust and ionized gas in the 500 central pc of the
  Galaxy

abstract:
  We present infrared and millimeter observations of molecular gas, dust and
ionized gas towards a sample of clouds distributed along the 500 central pc of
the Galaxy. The clouds were selected to investigate the physical state, in
particular the high gas temperatures, of the Galactic center region (GCr)
clouds located far from far-infrared of thermal radio continuum sources. We
have found that there is ionized gas associated with the molecular gas. The
ionizing radiation is hard (~35000 K) but diluted due to the inhomogeneity of
the medium. We estimate that ~30 % of the warm molecular gas observed in the
GCr clouds is heated by ultra-violet radiation in photo-dissociation regions.


title: Extended photoionization and photodissociation in Sgr B2

abstract:
  We present large scale 9' x 27' (25 pc x 70 pc) far-IR observations of the
Sgr B2 complex using the spectrometers on board the Infrared Space Observatory
(ISO). The far-IR spectra are dominated by the strong continuum emission of
dust and by the fine structure lines of high excitation potential ions (NII,
NIII and OIII) and those of neutral or weakly ionized atoms (OI and CII). The
line emission has revealed a very extended component of ionized gas. The study
of the NIII 57 microns/NII 122 microns and OIII 52/88 microns line intensity
ratios show that the ionized gas has a density of n_e~10^{2-3} cm^-3 while the
ionizing radiation can be characterized by a diluted but hard continuum, with
effective temperatures of ~35000 K.
  Photoionization models show that the total number of Lyman photons needed to
explain such an extended component is approximately equal to that of the HII
regions in Sgr B2(N) and (M) condensations. We propose that the inhomogeneous
and clumpy structure of the cloud allows the radiation to reach large distances
through the envelope. Therefore, photodissociation regions (PDRs) can be
numerous at the interface of the ionized and the neutral gas. The analysis of
the OI (63 and 145 microns) and CII (158 microns) lines indicates an incident
far-UV field (G_0, in units of the local interstellar radiation field) of
10^{3-4} and a H density of 10^{3-4} cm^{-3} in such PDRs. We conclude that
extended photoionization and photodissociation are also taking place in Sgr B2
in addition to more established phenomena such as widespread low--velocity
shocks.


title:
Discovery of a short plateau phase in the early evolution of a gamma-ray
  burst afterglow

abstract:
  We report optical observations during the first hour of the gamma-ray burst
(GRB) afterglow of GRB021004. Our observation revealed the existence of a short
plateau phase, in which the afterglow remained at almost constant brightness,
before an ordinary rapid fading phase. This plateau phase lasted for about 2
hours from 0.024 to 0.10 d after the burst, which corresponds to a missing
blank of the early afterglow light curve of GRB990123. We propose that the
plateau phase can be interpreted as the natural evolution of synchrotron
emission from the forward shock region of a blast wave. The time when the
typical frequency of the synchrotron emission passes through the optical range
has been predicted to be about 0.1 d after the burst, which is consistent with
the observed light curve. Our scenario hence implies that the observed feature
in GRB021004 is a common nature of GRB afterglows.


title: Superbubbles vs Super-galactic winds

abstract:
  We stress some of the major differences between supergalactic winds and giant
superbubbles evolving into the giant low density haloes of galaxies. We review
major properties of bursts of star formation and the critical energy required
for mass ejection both in the case of an ISM strongly flattened by rotation and
that imposed by a more extended ISM distribution arising from a smaller
rotation. The limits are thus establish for galaxies with an ISM mass in the
range 10$^6$ M$_\odot$ to more than 10$^9$ M$_\odot$, and are compared with a
sample of local galaxies. Some of these galaxies seem to be above the critical
limit despite the fact that their structure is clearly that of a superbubble.
True supergalactic winds, as evidence by M82, are shown to exceed the critical
limit by more than an order of magnitude and thus the limit derived by Silich &
Tenorio-Tagle (2001) for mass ejection should be regarded as a lower limit.


title: Early Preheating and Galaxy Formation

abstract:
  Winds from pregalactic starbursts and 'miniquasars' may pollute the IGM with
metals and raise its temperature to a high adiabat, and so inhibit the
formation of early galaxies. We compute the thermal history of the IGM when it
experiences a period of rapid, homogeneous "preheating" at high redshifts.
Measurements of the temperature of the Lyamn-alpha forest at z~3 constrain the
redshift and energy of preheating, and rule out models that preheat too late or
to too high a temperature. We predict galaxy luminosity functions in preheated
universes. The results depend crucially on whether the baryonic smoothing scale
in the IGM is computed globally, or in a local, density-dependent fashion.
Using a globally averaged smoothing scale, we find that models with excessive
preheating produce too few L_* and fainter galaxies, and are therefore
inconsistent with observational data. A density-dependent smoothing scale
requires more energetic preheating to achieve the same degree of suppression in
the faint-end slope. All models, however, appear unable to explain the sharp
cut-off in the luminosity function at bright magnitudes. Supernova-driven
preheating scenarios tend to raise the mean metallicity of the universe well
above the minimum levels observed in the Lyman-alpha clouds. We find that
ionizing photon escape fractions must be significantly higher than 10% in order
to explain the low inferred HI fraction at z~6. While early preheating causes
strong suppression of dwarf galaxy formation we show that it is not able to
reproduce the observed abundance of satellite galaxies in the Local Group in
detail.


title: First NH3 detection of the Orion Bar

abstract:
  Odin has successfully observed three regions in the Orion A cloud, i.e. Ori
KL, Ori S and the Orion Bar, in the 572.5 GHz rotational ground state line of
ammonia, ortho-NH3 (J,K) = (1,0) -> (0,0), and the result for the Orion Bar
represents the first detection in an ammonia line. Several velocity components
are present in the data. Specifically, the observed line profile from the Orion
Bar can be decomposed into two components, which are in agreement with
observations in high-J CO lines by Wilson et al. 2001. Using the source model
for the Orion Bar by these authors, our Odin observation implies a total
ammonia abundance of NH3/H2 = 5E-9.


title: On the Luminosity of the Ultra High Energy Cosmic Rays Sources

abstract:
  The energy density of the Ultra High Energy Cosmic Rays (UHECR) in the
Universe is a very important parameter for the solution of the puzzle of their
origin. It defines the luminosity of the UHECR sources and thus the type of
objects they are.
  This is also of crucial importance for the design of high energy neutrino
telescopes. The current attempts to derive the source luminosity are hindered
by the small world experimental statistics.
  We show that the unknown strength and structure of the large scale cosmic
magnetic fields affect strongly the UHECR propagation history.
  The identification of the UHECR sources will bring important information on
the large scale magnetic fields.


title:
Unveiling the nature of the 321s Orbital Period X-ray source RX
  J0806.3+1527

abstract:
  A nearly simultaneous X-ray/optical (Chandra and VLT) observational campaign
of RX J0806.3+1527 has been carried out during November 2001. These
observations allowed us to phase the X-ray and optical light curves for the
first time. We measured a phase-shift of about 0.5, in good agreement with the
presence of two distinct emission regions and with the X-ray irradiation
process predictions. The Chandra data allowed us also to study in details the
X-ray spectrum of RX J0806.3+1527, which is consistent with a soft (kT<70 eV)
and small (R_BB<20 km) blackbody component. We discuss the present findings on
the light of the models proposed so far to account for the X-ray emission
detected from RX J0806.3+1527, and its twin source RX J1914.4+2456.


title: Relativistic parsec-scale jets: I. Particle acceleration

abstract:
  We develop a theory of particle acceleration inside relativistic rotating
electron-positron force-free jets with spiral magnetic fields. We considered
perturbation of the stationary magnetic field structure and found that
acceleration takes place in the regions where the Alfven resonant condition
with the eigenmodes in the jet is fulfilled, i.e. where the local Alfven speed
is equal to the phase speed of an eigenmode. The acceleration mechanism is
regular acceleration by the electric field of the electromagnetic wave, which
is the eigenmode of the force-free cylindrical jet: particles drift out of the
region of the large wave amplitude near the Alfven resonant surface and gain
energy. Acceleration in the strong electric field near the Alfven resonance and
synchrotron losses combine to form a power-law energy spectrum of
ultra-relativistic electrons and positrons with index between 2 and 3 depending
upon the initial energy of the injected particles. The power law distribution
ranges from 10 MeV to 1000 MeV.


title: The Nearby Neutron Star RX J0720.4-3125 from Radio to X-rays

abstract:
  We present radio, optical, ultraviolet, and X-ray observations of the
isolated, thermally-emitting neutron star RX J0720.4-3125 using the Parkes
radio telescope, the Very Large Array, the Hubble Space Telescope, and the
Chandra X-ray Observatory. From these data we show that the optical/UV spectrum
of RX J0720.4-3125 is not well fit by a Rayleigh-Jeans tail as previously
thought, but is instead best fit by either a single non-thermal power-law or a
combination of a Rayleigh-Jeans tail and a non-thermal power-law. Taken
together with the X-ray spectrum, we find the best model for RX J0720.4-3125 to
be two blackbodies plus a power-law, with the cool blackbody implying a radius
of 11-13 km at an assumed distance of 300 pc. This is similar to many middle
aged (10^{5-6} yr) radio pulsars such as PSR B0656+14, evidence supporting the
hypothesis that RX J0720.4-3125 is likely to be an off-beam radio pulsar. The
radio data limit the flux at 1.4 GHz to be <0.24 mJy, or a luminosity limit of
4*pi*d^2*F < 3e25*d_300^2 ergs/s, and we see no sign of extended nebulosity,
consistent with expectations for a pulsar like RX J0720.4-3125.


title: Is the Low CMB Quadrupole a Signature of Spatial Curvature?

abstract:
  The temperature anisotropy power spectrum measured with the Wilkinson
Microwave Anisotropy Probe (WMAP) at high multipoles is in spectacular
agreement with an inflationary Lambda-dominated cold dark matter cosmology.
However, the low order multipoles (especially the quadrupole) have lower
amplitudes than expected from this cosmology, indicating a need for new
physics. Here we speculate that the low quadrupole amplitude is associated with
spatial curvature. We show that positively curved models are consistent with
the WMAP data and that the quadrupole amplitude can be reproduced if the
primordial spectrum truncates on scales comparable to the curvature scale.


title: A Vigorous Starburst in the SCUBA Galaxy N2 850.4

abstract:
  We present optical and near-IR spectroscopy of a z=2.38 hyperluminous IR
galaxy, covering the restframe wavelength range from 1000-5000A. It appears to
comprise two components separated by less than 1" on the sky (<8kpc); one
component (B) is blue, the other (P) is red in restframe UV-optical colours.
The combined system has an optical luminosity of ~8L* and its restframe optical
spectrum is characteristic of a Seyfert AGN. However, its restframe UV spectrum
exhibits striking features associated with young stars, including P-Cygni lines
from stellar winds and blue-shifted interstellar absorption lines indicative of
a galactic outflow. Redshifts are derived from stellar photospheric lines in
the UV and from narrow emission lines in the restframe optical, and these are
compared to that measured for the molecular gas recently detected with the IRAM
interferometer. The offsets indicate that the far-IR emission is most likely
associated with the near-IR source P, which hosts the Seyfert nucleus, while
the UV-bright component B is blueshifted by 400km/s. This suggests that the two
components are probably merging and the resulting gravitational interactions
have triggered the hyperluminous activity. Modelling of the UV spectral
features implies that the starburst within the UV component of this system has
been going on for at least ~10Myrs. Assuming that the bolometrically-dominant
obscured component has a similar lifetime, we estimate that it has so far
formed a total stellar mass of ~10^11 Mo. If this star formation continues at
its present level for substantially longer, or if this activity is repeated,
then the present-day descendant of N2 850.4 will be a very luminous galaxy.


title: The Earliest Epoch of Reionisation in the Standard $\Lambda$CDM Model

abstract:
  We show that the earliest possible reionisation of the Universe is
approximately at $z\simeq 13.5$ and the optical depth is $\tau\simeq 0.17$ in
the conventionally accepted $\Lambda$ cold dark matter ($\Lambda$CDM) model
with adiabatic fluctuations of a flat spectrum normalised to the cosmic
microwave background. This is consistent with the reionisation found by WMAP
(the apparently earlier reionisation epoch of the WMAP is ascribed to the
adoption of the instantaneous reionisation approximation), i.e., the WMAP
result is realised only if reionisation of the universe takes place nearly at
the maximal efficiency in the $\Lambda$CDM model.


title: The Survival of Bars with Central Mass Concentrations

abstract:
  Many barred galaxies today harbor massive concentrations of gas in their
centers, and some are known to possess supermassive black holes (SBHs) and
their associated stellar cusps. Previous theoretical work has suggested that a
bar in a galaxy could be dissolved by the formation of a mass concentration in
the center, although the precise mass and degree of central concentration
required is not well-established. Here we report an extensive study of the
effects of central masses on bars in high-quality N-body simulations of
galaxies. We study models containing both strong and weak bars, and quantify
the change in bar amplitude as a mass concentration is grown in their centers.
We find that bars are more robust than previously thought. We have varied the
growth rate of the central mass, its final mass and the degree of concentration
of the mass. Our main conclusions are: (1) the central mass has to be as large
as several percent of the disk mass to completely destroy the bar; (2) for a
given mass, objects whose scale-length is a few pc or less cause the greatest
reduction in bar amplitude, while significantly more diffuse objects have a
lesser effect; and (3) the bar amplitude always decreases as the central mass
is grown, and continues to decay thereafter on a cosmological timescale. Thus
the masses of SBHs are probably too small, even when dressed with a stellar
cusp, to affect the bar amplitude significantly.


title: High Frequency Peakers

abstract:
  There is quite a clear anticorrelation between the intrinsic peak frequency
and the overall radio source size in Compact Steep Spectrum (CSS) and GHz
Peaked Spectrum (GPS) radio sources as shown by O'Dea (1998). This feature is
interpreted in terms of synchrotron self-absorption (although free-free
absorption may play a role as well) of the radiation emitted by a small radio
source which is growing within the inner region of the host galaxy. This leads
to the hypothesis that these objects are young and that the radio source is
still developing/expanding within the host galaxy itself. Very young radio
sources must have the peak in their radio spectra occurring above a few tens of
GHz, and for this reason they are termed High Frequency Peakers (HFPs). These
newly born radio sources must be very rare given that they spend very little
time in this stage.


title:
First detection of NH3 (1,0 - 0,0) from a low mass cloud core: On the
  low ammonia abundance of the rho Oph A core

abstract:
  Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz
rotational ground state line of ammonia, NH3 (J,K = 1,0 - 0,0). The
interpretation of this result makes use of complementary molecular line data
obtained from the ground (C17O and CH3OH) as part of the Odin preparatory work.
Comparison of these observations with theoretical model calculations of line
excitation and transfer yields a quite ordinary abundance of methanol, X(CH3OH)
= 3e-9. Unless NH3 is not entirely segregated from C17O and CH3OH, ammonia is
found to be significantly underabundant with respect to typical dense core
values, viz. X(NH3) = 8e-10.


title: The complete Z-diagram of LMC X-2

abstract:
  We present results from four Rossi X-ray Timing Explorer (RXTE) observations
of the bright low mass X-ray binary LMC X-2. During these observations, which
span a year and include over 160 hrs of data, the source exhibits clear
evolution through three branches on its hardness-intensity and color-color
diagrams, consistent with the flaring, normal, and horizontal branches (FB, NB,
HB) of a Z-source, and remarkably similar to Z-tracks derived for GX 17+2, Sco
X-1 and GX 349+2. LMC X-2 was observed in the FB, NB, and HB for roughly 30%,
40%, and 30% respectively of the total time covered. The source traces out the
full extent of the Z in ~1 day, and the Z-track shows evidence for secular
shifts on a timescale in excess of a few days. Although the count rate of LMC
X-2 is low compared with the other known Z-sources due to its greater distance,
the power density spectra selected by branch show very-low-frequency noise
characteristics at least consistent with those from other Z-sources. We thus
confirm the identification of LMC X-2 as a Z-source, the first identified
outside our Galaxy.


title: Hot Molecular Gas in the Central 10 Parsecs of the Galaxy

abstract:
  We present results from observations of NH_3(1,1), (2,2), (3,3), and (6,6)
with the Very Large Array. The data sample the inner 10 pc (4') of the Galaxy
and have a velocity coverage of -140 to +130 km/s. The velocity integrated
NH_3(3,3) image shows that the Sgr A East supernova remnant is impacting the 50
km/s GMC in the northeast, the northern ridge in the north, and the western
streamer in the west. These results imply that the Sgr A East has a large
effect on the molecular environment near Sgr A* and may be pushing much of the
molecular gas away from Sgr A*. The physical properties of the western streamer
and its relation to Sgr A East are discussed in detail. We also summarize the
detection of hot molecular gas less than 2 pc from Sgr A* in projected
distance. This gas is seen only in NH_3(6,6) and has line widths of 75-85 km/s,
indicating that it is physically close to the nucleus.


title:
Galaxy Mass Distributions from Rotation Speeds by Closed-Loop
  Convergence

abstract:
  Given the dimensions (including thickness) and rotation speeds for an
axisymmetric galaxy, a closed-loop iterative method is designed to find the
total mass, density, and surface-mass density (SMD)distributions. There is no
need for dark-matter halos. Density accuracy of course depends on the accuracy
of the thickness data, but SMD and total mass are as good as the inputs of
rotation speeds vs radius if reasonable estimates are made for thickness. The
effects of an exponential "atmosphere" are included.


title:
Discovery of type-I X-ray bursts from the low-mass X-ray binary 4U
  1708-40

abstract:
  We report the discovery of type-I X-ray bursts from the low-mass X-ray binary
4U 1708-40 during the 100 ks observation performed by BeppoSAX on 1999 August
15-16. Six X-ray bursts have been observed. The unabsorbed 2-10 keV fluxes of
the bursts range from ~ (3-9)x10^(-10) erg cm^(-2)s^(-1). A correlation between
peak flux and fluence of the bursts is found, in agreement with the behaviour
observed in other similar sources. There is a trend of the burst flux to
increase with the time interval from the previous burst. From the value of the
persistent flux we infer a mass accretion rate Mdot~7x10^(-11) Msun/yr, that
may correspond to the mixed hydrogen/helium burning regime triggered by
thermally unstable hydrogen. We have also analysed a BeppoSAX observation
performed on 2001 August 22 and previous RXTE observations of 4U 1708-40, where
no bursts have been observed; we found persistent fluxes of more than a factor
of 7 higher than the persistent flux observed during the BeppoSAX observation
showing X-ray bursts.


title: Stellar sources in the ISOGAL intermediate bulge fields

abstract:
  We present a study of ISOGAL sources in the "intermediate" galactic bulge
($|$$l$$|$ $<$ 2$^\circ$, $|$$b$$|$ $\sim$ 1$^\circ$--4$^\circ$), observed by
ISOCAM at 7 and 15 $\mu m$. In combination with near-infrared (I, J, K$_{\rm
s}$) data of DENIS survey, complemented by 2MASS data, we discuss the nature of
the ISOGAL sources, their luminosities, the interstellar extinction and the
mass-loss rates. A large fraction of the 1464 detected sources at 15 $\mu m$
are AGB stars above the RGB tip, a number of them show an excess in
([7]-[15])$_{\rm 0}$ and (K$_{\rm s}$-[15])$_{\rm 0}$ colours, characteristic
of mass-loss. The latter, especially (K$_{\rm s}$-[15])$_{\rm 0}$, provide
estimates of the mass-loss rates and show their distribution in the range
10$^{-8}$ to 10$^{-5}$ M$_{\rm \odot}$/yr.


title: The Hanle Effect as a Magnetic Diagnostic

abstract:
  The physics of the Hanle effect is briefly reviewed, and its application as a
diagnostic of hot star magnetic fields is described. Emphasis is given to the
practicalities of using spectropolarimetry of resolved wind emission lines to
infer information about the circumstellar magnetic field strength and its
geometry. A model for a weakly magnetized wind from "WCFields" theory is used
as the backdrop for investigating polarized line profile effects for P Cygni
resonance lines using a kind of "last scattering approximation". Model results
are presented for a typical P Cygni line that forms in a spherical wind.
Significant line polarizations of a few tenths of a percent can result for
circumstellar fields of order 100G. Information about the field topology and
surface field strength is gleaned from the Stokes-Q and U-profiles.
Simplistically, the Q-profile polarization is governed by the field strength,
and the U-profile symmetry (whether symmetric or anti-symmetric or even zero)
is governed by the field geometry.


title: Submillimeter Emission from Water in the W3 Region

abstract:
  We have mapped the submillimeter emission from the 1(10)-1(01) transition of
ortho-water in the W3 star-forming region. A 5'x5' map of the W3 IRS4 and W3
IRS5 region reveals strong water lines at half the positions in the map. The
relative strength of the Odin lines compared to previous observations by SWAS
suggests that we are seeing water emission from an extended region. Across much
of the map the lines are double-peaked, with an absorption feature at -39 km/s;
however, some positions in the map show a single strong line at -43 km/s. We
interpret the double-peaked lines as arising from optically thick,
self-absorbed water emission near the W3 IRS5, while the narrower blue-shifted
lines originate in emission near W3 IRS4. In this model, the unusual appearance
of the spectral lines across the map results from a coincidental agreement in
velocity between the emission near W3 IRS4 and the blue peak of the more
complex lines near W3 IRS5. The strength of the water lines near W3 IRS4
suggests we may be seeing water emission enhanced in a photon-dominated region.


title: On the linear filters for point source extraction of the Planck mission

abstract:
  The manifestation of point sources in the upcoming PLANCK maps is a direct
reflection of the properties of the pixelized antenna beam shape for each
frequency, which is related to the scan strategy, pointing accuracy, noise
properties and map-making algorithm. In this paper we firstly compare
analytically two filters for the PLANCK point source extraction, namely, the
adaptive top-hat filter (ATHF), the theoretically-optimal filter (TOF). Our
analyses are based on the premise that the experiment parameters the TOF assume
and require are already known: the CMB and noise power spectrum and a circular
Gaussian beam shape and size, whereas the ATHF does not need any a priori
knowledge. The analyses show that the TOF is optimal in terms of the gain after
the parameter inputs. We simulate the PLANCK HFI 100 GHz channel with
elliptical beam in rotation to test the efficiency of the TOF and the ATHF. We
also apply the ATHF on the WMAP Q-band map and the derived map (the
foreground-cleaned map by Tegmark, de Oliveira Costa & Hamilton) from the WMAP
1-year data. The uncertainties on the angular power spectrum will hamper the
efficiency of the TOF. To tackle the real situations for the PLANCK point
source extraction, most importantly, the elliptical beam shape with slow
precession and change of the ellipticity ratio due to possible mirror
degradation effect, the ATHF is computationally efficient and well suited for
the construction of the PLANCK Early Release Compact Source Catalogue.


title: A Chandra Study of the Dense Globular Cluster Terzan 5

abstract:
  We report a Chandra ACIS-I observation of the dense globular cluster Terzan
5. The previously known transient low-mass x-ray binary (LMXB) EXO 1745-248 in
the cluster entered a rare high state during our August 2000 observation,
complicating the analysis. Nevertheless nine additional sources clearly
associated with the cluster are also detected, ranging from L_X(0.5-2.5
keV)=5.6*10^{32} down to 8.6*10^{31} ergs/s. Their X-ray colors and
luminosities, and spectral fitting, indicate that five of them are probably
cataclysmic variables, and four are likely quiescent LMXBs containing neutron
stars. We estimate the total number of sources between L_X(0.5-2.5 keV)=10^{32}
and 10^{33} ergs/s as 11.4^{+4.7}_{-1.8} by the use of artificial point source
tests, and note that the numbers of X-ray sources are similar to those detected
in NGC 6440. The improved X-ray position allowed us to identify a plausible
infrared counterpart to EXO 1745-248 on our 1998 Hubble Space Telescope NICMOS
images. This blue star (F110W=18.48, F187W=17.30) lies within 0.2'' of the
boresighted LMXB position. Simultaneous Rossi X-ray Timing Explorer (RXTE)
spectra, combined with the Chandra spectrum, indicate that EXO 1745-248 is an
ultracompact binary system, and show a strong broad 6.55 keV iron line and an 8
keV smeared reflection edge.


title: Stellar Motions in the Polar Ring Galaxy NGC 4650A

abstract:
  We present the first measurement of the stellar kinematics in the polar ring
of NGC 4650A. There is well defined rotation, with the stars and gas rotating
in the same direction, and with similar amplitude. The gaseous and stellar
kinematics suggest an approximately flat rotation curve, providing further
support for the hypothesis that the polar material resides in a disk rather
than in a ring. The kinematics of the emission line gas at and near the center
of the S0 suggests that the polar disk lacks a central hole. We have not
detected evidence for two, equal mass, counterrotating stellar polar streams,
as is predicted in the resonance levitation model proposed by Tremaine & Yu. A
merger seems the most likely explanation for the structure and kinematics of
NGC 4650A.


title:
Iron K alpha line profiles and the inner boundary condition of accretion
  flows

abstract:
  Recent X-ray observations have shown evidence for exceptionally broad and
skewed iron K alpha emission lines from several accreting black hole systems.
The lines are assumed to be due to fluorescence of the accretion disk
illuminated by a surrounding corona and require a steep emissivity profile
increasing in to the innermost radius. This appears to question both standard
accretion disc theory and the zero torque assumption for the inner boundary
condition, both of which predict a much less extreme profile. Instead it argues
that a torque may be present due to magnetic coupling with matter in the
plunging region or even to the spinning black hole itself. Discussion so far
has centered on the torque acting on the disc. However the crucial determinant
of the iron line profile is the radial variation of the power radiated in the
corona. Here we study the effects of different inner boundary conditions on the
coronal emissivity and on the profiles of the observable Fe K alpha lines. We
argue that in the extreme case where a prominent highly redshifted component of
the iron line is detected, requiring a steep emissivity profile in the
innermost part and a flatter one outside, energy from the gas plunging into the
black hole is being fed directly to the corona.


title:
Discovery of variable circular polarization from the remnant of Nova
  Chamaeleontis 1953 (RR Cha)

abstract:
  We report on the discovery of variable circular polarization from the remnant
of Nova Chamaeleontis 1953 (RR Cha). The circular polarization appears to be
modulated on the primary's spin period and harmonics of the positive superhump
period, with an amplitude peak-to-peak of almost ~10 per cent with both
negative and positive polarization. A recent study by Woudt & Warner of RR Cha
shows it to have both positive and negative superhumps, indicating the presence
of a precessing/tilted accretion disc. In addition, they also find a stable
period at 1950 s, characteristic of an Intermediate Polar. RR Cha also shows
deep eclipses with variable depth. We propose a possible explanation for the
origin of the polarized emission. We assume that it is of cyclotron origin. The
variations of the circular polarization with the proposed spin period are
caused by the rotation of the compact object. The long period variability arise
as a result of a precessing/tilted accretion disc, periodically obscuring
either of two accretion regions on the surface of the white dwarf. We also
point out several similarities of RR Cha with the SW Sex stars. The lack of a
time resolved spectroscopic study prevents to make any conclusion regarding its
possible SW Sex nature. Hence, such spectroscopic study is encouraged. RR Cha
is the second old nova exhibiting variable circular polarization and we
therefore encourage polarimetric observations of other nova remnants.


title: Interacting quintessence solution to the coincidence problem

abstract:
  We show that a suitable interaction between a scalar field and a matter fluid
in a spatially homogeneous and isotropic spacetime can drive the transition
from a matter dominated era to an accelerated expansion phase and
simultaneously solve the coincidence problem of our present Universe. For this
purpose we study the evolution of the energy density ratio of these two
components. We demonstrate that a stationary attractor solution is compatible
with an accelerated expansion of the Universe. We extend this study to account
for dissipation effects due to interactions in the dark matter fluid. Finally,
Type Ia supernovae and primordial nucleosynthesis data are used to constrain
the parameters of the model.


title: Luminosity segregation versus fractal scaling in the galaxy distribution

abstract:
  In this letter I present results from a correlation analysis of three galaxy
redshift catalogs: the SSRS2, the CfA2 and the PSCz. I will focus on the
observation that the amplitude of the two--point correlation function rises if
the depth of the sample is increased. There are two competing explanations for
this observation, one in terms of a fractal scaling, the other based on
luminosity segregation. I will show that there is strong evidence that the
observed growth is due to a luminosity dependent clustering of the galaxies.


title: Atomic Spectral Features During Thermonuclear Flashes on Neutron Stars

abstract:
  The gravitational redshift measured by Cottam, Paerels and Mendez for the
neutron star (NS) in the low-mass X-ray binary EXO 0748-676 depends on the
identification of an absorption line during a type I burst as the H$\alpha$
line from hydrogenic Fe. We show that Fe is present above the photosphere as
long as $\dot M>4\times 10^{-13}M_\odot {\rm yr^{-1}}$ during the burst. In
this limit, the total Fe column is $N_{\rm Fe}\approx 3\times 10^{19}{\rm
cm^{-2}}$ for incident material of solar abundances and only depends on the
nuclear physics of the proton spallation. The Fe destruction creates many heavy
elements with $Z<26$ which may imprint photo-ionization edges on the NS spectra
during a radius expansion event or in a burst cooling tail. Detecting these
features in concert with those from Fe would confirm a redshift measurement. We
also begin to address the radiative transfer problem, and find that a
concentrated Fe layer with $kT=1.2-1.4 {\rm keV}$ and column $N_{\rm Fe}= 7-20
\times 10^{20} {\rm cm}^{-2}$ (depending on the line depth) above the hotter
continuum photosphere is required to create the H$\alpha$ line of the observed
strength. This estimate must be refined by considerations of non-LTE effects as
well as resonant line transport. Until these are carried out, we cannot say
whether the Fe column from accretion and spallation is in conflict with the
observations. We also show that hydrogenic Fe might remain in the photosphere
due to radiative levitation from the high burst flux.


title: Relaxation of writhe and twist of a bi-helical magnetic field

abstract:
  In the past few years suggestions have emerged that the solar magnetic field
might have a bi-helical component with oppositely polarized magnetic fields at
large and small scales, and that the shedding of such fields may be crucial for
the operation of the dynamo. It is shown that, if a bi-helical field is shed
into the solar wind, positive and negative contributions of the magnetic
helicity spectrum tend to mix and decay. Even in the absence of turbulence,
mixing and decay can occur on a time scale faster than the resistive one
provided the two signs of magnetic helicity originate from a single tube. In
the presence of turbulence, positively and negatively polarized contributions
mix rapidly in such a way that the ratio of magnetic helicity to magnetic
energy is largest both at the largest scale and in the dissipation range. In
absolute units the small scale excess of helical fields is however negligible.


title:
A New Method to Use Chandra Data to Resolve the X-Ray Halos Around Point
  Sources and Its Application to Cygnus X-1

abstract:
  With excellent angular resolution, good energy resolution and broad energy
band, the Chandra ACIS is the best instrument for studying the X-ray halos
around some galactic X-ray point sources caused by the dust scattering of
X-rays in the interstellar medium. However, the direct images of bright sources
obtained with ACIS usually suffer from severe pile-up. Making use of the fact
that an isotropic image could be reconstructed from its projection into any
direction, we can reconstruct the images of the X-ray halos from the data
obtained with the HETGS and/or in CC mode. These data have no or less serious
pile-up and enable us to take full advantage of the excellent angular
resolution of Chandra. With the reconstructed high resolution images, we can
probe the X-ray halos as close as 1$''$ to their associated point sources.
Applying this method to Cygnus X-1 observed with Chandra HETGS in CC mode, we
derived an energy dependent radial halo flux distribution and concluded that,
in a circular region (2$'$ in radius) centered at the point source: (1)
relative to the total intensity, the fractional halo intensity (FHI) is about
15% at $\sim$1 keV and drops to about 5% at $\sim$6 keV; (2) about 50% of the
halo photons are within the region of a radius less than 40$''$; and (3) the
spectrum of the point source is slightly distorted by the halo contamination.


title: Confronting the IR Fixed Point Cosmology with High Redshift Observations

abstract:
  We use high-redshift type Ia supernova and compact radio source data in order
to test the infrared (IR) fixed point model of the late Universe which was
proposed recently. It describes a cosmology with a time dependent cosmological
constant and Newton constant whose dynamics arises from an underlying
renormalization group flow near an IR-attractive fixed point. Without any
finetuning or quintessence field it yields $\Omega_{\rm
M}=\Omega_{\Lambda}=1/2$. Its characteristic $t^{4/3}$-dependence of the scale
factor leads to a distance-redshift relation whose predictions are compared
both to the supernova and to the radio source data. According to the $\chi^2$
test, the fixed point model reproduces the data at least as well as the
best-fit (Friedmann-Robertson-Walker) standard cosmology.Furthermore, we extend
the original fixed point model by assuming that the fixed point epoch is
preceded by an era with constant $G$ and $\Lambda$. By means of a Monte Carlo
simulation we show that the data expected from the forthcoming SNAP satellite
mission could detect the transition to the fixed point regime provided it took
place at a redshift of less than about 0.5.


title:
Full Three Dimensional Orbits For Multiple Stars on Close Approaches to
  the Central Supermassive Black Hole

abstract:
  With the advent of adaptive optics on the W. M. Keck 10 m telescope, two
significant steps forward have been taken in building the case for a
supermassive black hole at the center of the Milky Way and understanding the
black hole's effect on its environment. Using adaptive optics and speckle
imaging to study the motions of stars in the plane of sky with +-~2 mas
precision over the past 7 years, we have obtained the first simultaneous
orbital solution for multiple stars. Among the included stars, three are newly
identified (S0-16, S0-19, S0-20). The most dramatic orbit is that of the newly
identified star S0-16, which passed a mere 60 AU from the central dark mass at
a velocity of 9,000 km/s in 1999. The orbital analysis results in a new central
dark mass estimate of 3.6(+-0.4)x10^6(D/8kpc)^3 Mo. This dramatically
strengthens the case for a black hole at the center of our Galaxy, by confining
the dark matter to within a radius of 0.0003 pc or 1,000 Rsh and thereby
increasing the inferred dark mass density by four orders of magnitude compared
to earlier estimates.
  With the introduction of an adaptive-optics-fed spectrometer, we have
obtained the spectra of these high-velocity stars, which suggest that they are
massive (~15 Mo), young (<10 Myr) main sequence stars. This presents a major
challenge to star formation theories, given the strong tidal forces that
prevail over all distances reached by these stars in their current orbits and
the difficulty in migrating these stars inward during their lifetime from
further out where tidal forces should no longer preclude star formation.


title:
Optical photometry and X-ray monitoring of the "Cool Algol" BD+05 706:
  Determination of the physical properties

abstract:
  We present new photometric observations in the BVRI bands of the double-lined
eclipsing binary BD+05 706 conducted over three observing seasons, as well as
new X-ray observations obtained with the ROSAT satellite covering a full
orbital cycle (P = 18.9 days). A detailed light-curve analysis of the optical
data shows the system to be semidetached, confirming indications from an
earlier analysis by Torres et al. (1998), with the less massive and cooler star
filling its Roche lobe. The system is a member of the rare class of cool Algol
systems, which are different from the "classical" Algol systems in that the
mass-gaining component is also a late-type star rather than a B- or A-type
star. By combining the new photometry with a reanalysis of the spectroscopic
observations reported by Torres et al. (1998) we derive accurate absolute
masses for the components of M1 = 2.633 +/- 0.028 Msun and M2 = 0.5412 +/-
0.0093 Msun, radii of R1 = 7.55 +/- 0.20 Rsun and R2 = 11.02 +/- 0.21 Rsun, as
well as effective temperatures of 5000 +/- 100 K and 4640 +/- 150 K for the
primary and secondary, respectively. There are obvious signs of activity
(spottedness) in the optical light curve of the binary. Our X-ray light curve
clearly shows the primary eclipse but not the secondary eclipse, suggesting
that the primary star is the dominant source of the activity in the system. The
depth and duration of the eclipse allow us to infer some of the properties of
the X-ray emitting region around that star.


title: New Orbits for the n-Body Problem

abstract:
  In this paper, we consider minimizing the action functional as a method for
numerically discovering periodic solutions to the $n$-body problem. With this
method, we can find a large number of choreographies and other more general
solutions. We show that most of the solutions found, including all but one of
the choreographies, are unstable. It appears to be much easier to find unstable
solutions to the $n$-body problem than stable ones. Simpler solutions are more
likely to be stable than exotic ones.


title:
Doppler Images of the RS CVn Binary HR 1099 (V711 Tau) from the MUSICOS
  1998 Campaign

abstract:
  We present Doppler Images of the RS CVn binary system HR 1099 (V711
  Tau) from spectra taken in two different sites, KPNO and MSO, during the
MUSICO S 1998 campaign. Contemporaneous APT photometry is used to constrain the
Doppler Images. The resulting maximum entropy reconstructions based on the
least-square s deconvolved profiles, derived from $\sim$2000 photospheric
absorption lines, r eveal the presence of starspots at medium-high latitudes.
We have obtained maps for both components of the binary system for the first
time. The predominant str ucture in the primary component is an off-centered
polar spot, confirming previo us works on the same target by using independent
codes. The result is verified b y using both data sets independently. The lower
spectral resolution data set giv es a less detailed map for the MSO data set.
The images obtained for the seconda ry component show a low latitude spot
around orbital phase 0.7. This spot seems to mirror the structure seen on the
primary. It might suggest that tidal forces may influence the spot distribution
on this binary system.


title:
X-ray Spectra of Young Pulsars and Their Wind Nebulae: Dependence on
  Spin-down Energy

abstract:
  An observational model is presented for the spectra of young rotation-powered
pulsars and their nebulae based on a study of nine bright Crab-like pulsar
systems observed with the Chandra X-ray observatory. A significant correlation
is discovered between the X-ray spectra of these pulsars (PSRs) and that of
their associated pulsar wind nebulae (PWNe), both of which are observed to be a
function of the spin down energy, Edot . The 2 - 10 keV spectra of these
objects are well characterized by an absorbed power-law model with photon
indices, Gamma, in the range of 0.6 < Gamma_PSR < 2.1 and 1.3 < Gamma_PWN <
2.3, for the pulsars and their nebulae, respectively. A linear regression fit
relating these two sets of indexes yields, Gamma_PWN = 0.86 +/- 0.20 + (0.72
+/- 0.13) X Gamma_PSR, with a correlation coefficient of r = 0.96. The spectra
of these pulsars are found to steepen as Gamma = Gamma_max + alpha /
sqrt(Edot), with Gamma_max providing an observational limit on the spectral
slopes of young rotation-powered pulsars. These results reveal basic properties
of young pulsar systems, allow new observational constraints on models of
pulsar wind emission, and provide a means of predicting the energetics of such
systems when lacking detected pulsations.


title: Modeling Fluctuations in the GRB-Afterglow Light Curves

abstract:
  The fluctuations observed in the light curves of some GRB-afterglows (such as
GRB 021004) provide a useful tool to probe the circum-burst density profile and
to probe the variations in the energy of blast-wave with time. We present a
general formalism that reduces the calculation of the observed light curve from
a Blandford-Mackee blast-wave to the evaluation of a one dimensional integral.
Using this formalism we obtain a simple approximation to the general light
curve that arises in more complex situations where the afterglow's energy or
the external density vary. The solution is valid for spherically symmetric
profiles and it takes a full consideration of the angular time delay effects.
We present the light curves of several external density profiles and
demonstrate the effects of density variations on the light curve. We also
re-visit the afterglow of GRB021004 and we find that the steep decay after the
first bump ($\sim 4000sec$) cannot result from a spherically symmetric density
variation or from the passage of the synchrotron frequency through the optical
band. This suggests that an angular structure is responsible to some of the
observed features in the light curve. This may be the first evidence that an
angular structure is important in the early stages of the afterglow.


title:
Renewed activity in the radio galaxy PKS B1545-321: twin edge-brightened
  beams within diffuse radio lobes

abstract:
  Australia Telescope Compact Array (ATCA) images of the giant radio galaxy PKS
B1545-321 show a pair of oppositely directed beams emerging from a radio core
and ending in bright components that are symmetrically located on either side.
These inner beams are embedded within edge-brightened outer lobes of lower
surface brightness and the bright ends of the inner beams are well recessed
from the ends of the outer lobes. The inner beams and diffuse surrounding lobes
share a common central core and radio axis. We propose that the observed inner
beams are double lobes which have been created within relic outer lobes as a
consequence of a restarting of the central activity; therefore, PKS B1545-321
is a rare opportunity for examining the development of restarted beams within a
relic synchrotron plasma cocoon. The inner double representing the new episode
has among the highest axial ratios found in typical edge-brightened radio
galaxies. The low radio luminosity of the inner double, the narrow and constant
transverse extent of its cocoon and the relatively low brightness of the
hotspots at its ends are consistent with the almost ballistic propagation
expected for a beam that has a low density contrast and is advancing within a
relatively light ambient medium.


title:
Features of Motion Around Global Monopole in Asymptotically dS/AdS
  Spacetime

abstract:
  In this paper, we study the motion of test particle and light around the
Global Monopole in asymptotically dS/AdS spacetime. The motion of a test
particle and light in the exterior region of the global monopole in dS/AdS
spacetime has been investigated. Although the test particle's motion is quite
different from the case in asymptotically flat spacetime, the behaviors of
light(null geodesic) remain unchanged except a energy(frequency) shift. Through
a phase-plane analysis, we prove analytically that the existence of a periodic
solution to the equation of motion for a test particle will not be altered by
the presence of cosmological constant and the deficit angle, whose presence
only affects the position and type of the critical point on the phase plane. We
also show that the apparent capture section of the global monopole in dS/AdS
spacetime is quite different from that in flat spacetime.


title: The knee in galactic cosmic ray spectrum and variety in supernovae

abstract:
  The present paper deals with calculations based on a standard model of cosmic
ray acceleration in Supernova remnants (SNR) and on the latest astronomical
data concerning the variety in Supernovae types, energies as well as the sites
of their explosions. The results obtained allow explaination of the main
features of all particle cosmic ray spectrum, including the 'knee'. This
conclusion is based essentially on the premise that energy of accelerated CR in
the given SNR is proportional to the kinetic energy of this explosion, that
stresses the input of high energy explosions and suppresses the contribution of
low energy explosions to the total CR flux.


title: Dark energy, dissipation and the coincidence problem

abstract:
  In a recent paper we showed that a quintessence scalar field plus a
dissipative matter fluid can drive late cosmic accelerated expansion and
simultaneously solve the coincidence problem [1]. In this brief report we
extend this result to the cases when the scalar field is replaced either by a
Chaplygin gas or a tachyonic fluid.


title: Clumps in large scale relativistic jets

abstract:
  The relatively intense X-ray emission from large scale (tens to hundreds kpc)
jets discovered with Chandra likely implies that jets (at least in powerful
quasars) are still relativistic at that distances from the active nucleus. In
this case the emission is due to Compton scattering off seed photons provided
by the Cosmic Microwave Background, and this on one hand permits to have
magnetic fields close to equipartition with the emitting particles, and on the
other hand minimizes the requirements about the total power carried by the jet.
The emission comes from compact (kpc scale) knots, and we here investigate what
we can predict about the possible emission between the bright knots. This is
motivated by the fact that bulk relativistic motion makes Compton scattering
off the CMB photons efficient even when electrons are cold or mildly
relativistic in the comoving frame. This implies relatively long cooling times,
dominated by adiabatic losses. Therefore the relativistically moving plasma can
emit, by Compton scattering the microwave seed photons, for a long time. We
discuss how the existing radio--to--X-ray observations of large scale jets
already pose strong constraints on the structure and dynamics of knots and we
present a scenario that can satisfactorily reproduce the observed phenomenology
of the jet in 3C273. In this scenario the kiloparsec-scale knots visible with
HST, Chandra and VLA are composed of several smaller sub--units, accounting for
the fast decrease of the flux outside the large knot. Substructure in the
X-ray- emitting knots can also explain the month--year variability timescale
reported for the large scale jet in M87.


title: In the Kitchen of Dust Modeling

abstract:
  Dust grains have been detected in various astronomical objects.
Interpretation of observations of dusty objects includes three components: 1)
determination of the materials which can exist in the solid phase and the
measurements or acquisition of their optical constants; 2) selection of the
light scattering theory in order to convert the optical constants into the
optical properties of particles; and 3) the proper choice of the object model
which includes, in particular, the correct treatment of the radiative transfer
effects. The current state of the components of dust modeling and the
reliability of information obtained on the cosmic dust from transmitted,
scattered and emitted radiation are discussed.


title: A Significant Population of Red, Near-IR Selected High Redshift Galaxies

abstract:
  We use very deep near-infrared photometry of the Hubble Deep Field South
taken with ISAAC/VLT to identify a population of high redshift galaxies with
rest- frame optical colors similar to those of nearby galaxies. The galaxies
are chosen by their infrared colors Js-Ks > 2.3, aimed at selecting galaxies
with redshifts above 2. When applied to our dataset, we find 14 galaxies with
Ks < 22.5, corresponding to a surface density of 3+-0.8 /arcmin**2. The
photometric redshifts all lie above 1.9, with a median of 2.6 and a rms of 0.7.
The spectral energy distributions of these galaxies show a wide range: one is
very blue in the rest-frame UV, and satisfies the normal Lyman-break criteria
for high redshift, star-forming galaxies. Others are quite red throughout the
observed spectral range, and are extremely faint in the optical, with a median
V = 26.6. Hence these galaxies would not be included in photometric samples
based on optical ground-based data, and spectroscopic follow-up is difficult.
The spectral energy distributions often show a prominent break, identified as
the Balmer break or 4000 Ang. break. The median age is 1 Gyr when fit with a
constant star formation model with dust, or 0.7 Gyr when fit with a single
burst model. Although significantly younger ages cannot be excluded when a
larger range of models is allowed, the results indicate that these galaxies are
among the oldest at these redshifts. The volume density to Ks=22.5 is half that
of Lyman-break galaxies at z = 3. Since the mass-to-light ratios of the red
galaxies are likely to be higher, the stellar mass density is inferred to be
comparable to that of Lyman-break galaxies. These red galaxies may be the
descendants of galaxies which started to form stars at very high redshifts, and
they may evolve into the most massive galaxies at low redshift.


title: A new model of composite interstellar dust grains

abstract:
  The approach to model composite interstellar dust grains, using the exact
solution to the light scattering problem for multi-layered spheres as suggested
by Voshchinnikov & Mathis (1999), is further developed. Heterogeneous scatteres
are represented by particles with very large number of shells, each including a
homogeneous layer per material considered (amorphous carbon, astronomical
silicate and vacuum).
  The applicability of the effective medium theory (EMT) mostly utilized
earlier to approximate inhomogeneous interstellar grains is examined on the
basis of the new model.
  It is shown that the EMT rules generally have an accuracy of several percent
in the whole range of particle sizes provided the porosity does not exceed
about 50%.
  For larger porosity, the EMT rules give wrong results.
  Using the model, we reanalyze various basic features of cosmic dust --
interstellar extinction, scattered radiation, infrared radiation, radiation
pressure, etc. As an example of the potential of the model, it is applied to
reproduce the extinction curves in the directions to $\zeta$ Oph and $\sigma$
Sco using subsolar cosmic abundances. We also conclude that metallic iron even
in negligible amount ($\la 1$ % by the volume fraction) is unlikely to form a
layer on or inside a grain because of peculiar absorption of radiation by such
particles.


title:
Detection of strong clustering of red K-selected galaxies at 2<z_phot<4
  in the Hubble Deep Field South

abstract:
  The clustering properties of faint K<24 galaxies are measured in ultradeep J,
H and K near-IR images of the Hubble Deep Field South (HDF-S), obtained with
ISAAC at the VLT. A relatively large clustering amplitude is found up to K=24,
at a level comparable to the measurements at K~19. The redshift distribution of
K<24 galaxies extends to z_phot~4-5, and ~40% of the galaxies are at
z_phot>2.At the highest redshifts, 2<z_phot<4, galaxies selected in the rest
frame optical (K-band) appear more clustered than those selected in the rest
frame UV (i.e. Lyman Break Galaxies, LBGs). Galaxy clustering depends on the
J-K color at 2<z_phot<4. K-selected galaxies with J-K>1.7 reach r_0~8 h^-1 Mpc
comoving. This is a factor of 3--4 higher than the correlation length of LBGs
with similar number densities, down to V_606<27, and is also larger than the
correlation length of galaxies with blue J-K<1.7 colors. Hence at z about 3 a
color-density relation is observed which is similar to that observed locally.
Fluctuations in the amplitude of clustering due to cosmic variance may affect
our estimates derived from the small HDF-S field, but these are unlikely to
change our main conclusions. The galaxies with red J-K>1.7 colors at 2<z_phot<4
are likely older and more massive galaxies, on average, than LBGs. They were
presumably formed in the highest density perturbations at early epochs.
Semi-analytical hierarchical models do predict the existence of strongly
clustered populations at z~3, but with at least a factor of 10 lower number
density than the one measured. The overall properties of this strongly
clustered population consistently suggest that they are the progenitors, or
building blocks, of local massive early-type galaxies and z~1 EROs, close to
their major epochs of formation.


title:
Spectroscopic Confirmation of a Substantial Population of Luminous Red
  Galaxies at Redshifts z>2

abstract:
  We confirm spectroscopically the existence of a population of galaxies at
z>~2 with rest-frame optical colors similar to normal nearby galaxies. The
galaxies were identified by their red near-infrared colors in deep images
obtained with ISAAC on the Very Large Telescope. Redshifts of six galaxies with
Js-Ks>2.3 were measured from optical spectra obtained with the Keck Telescope.
Five out of six are in the range 2.43<=z<=3.52, demonstrating that the Js-Ks
color selection is quite efficient. The rest-frame ultraviolet spectra of
confirmed z>2 galaxies display a range of properties, with two galaxies showing
emission lines characteristic of AGN, two having Ly-alpha in emission, and one
showing interstellar absorption lines only. Their full spectral energy
distributions are well described by constant star formation models with ages
1.4-2.6 Gyr, except for one galaxy whose colors indicate a dusty starburst. The
confirmed z>2 galaxies are very luminous, with Ks=19.2-19.9. Assuming that our
bright spectroscopic sample is representative for the general population of
Js-Ks selected objects, we find that the surface density of red z>~2 galaxies
is ~0.9/arcmin^2 to Ks=21. The surface density is comparable to that of
Lyman-break selected galaxies with Ks<21, when corrections are made for the
different redshift distributions of the two samples. Although there will be
some overlap between the two populations, most 'optical-break' galaxies are too
faint in the rest-frame ultraviolet to be selected as Lyman-break galaxies. The
most straightforward interpretation is that star formation in typical
optical-break galaxies started earlier than in typical Lyman-break galaxies.
Optical-break galaxies may be the oldest and most massive galaxies yet
identified at z>2, and could evolve into early-type galaxies and bulges.


title: Chandra Observations of the Mice

abstract:
  Presented here are high spatial and spectral resolution Chandra X-ray
observations of the famous interacting galaxy pair, the Mice, a system similar
to, though less evolved than, the well-known Antennae galaxies. Previously
unpublished ROSAT HRI data of the system are also presented. Starburst-driven
galactic winds outflowing along the minor axis of both galaxies (but
particularly the northern) are observed, and spectral and spatial properties,
and energetics are presented. That such a phenomenon can occur in such a
rapidly-evolving and turbulent system is surprising, and this is the first time
that the very beginning - the onset, of starburst-driven hot gaseous outflow in
a full-blown disk-disk merger has been seen. Point source emission is seen at
the galaxy nuclei, and within the interaction-induced tidal tails. Further
point source emission is associated with the galactic bar in the southern
system. A comparison of the source X-ray luminosity function and of the diffuse
emission properties is made with the Antennae and other galaxies, and evidence
of a more rapid evolution of the source population than the diffuse component
is found. No evidence for variability is found between the Chandra and previous
observations.


title: Inflation in Gauss-Bonnet Brane Cosmology

abstract:
  The effect of including a Gauss-Bonnet contribution in the bulk action is
investigated within the context of the steep inflationary scenario. When
inflation is driven by an exponential inflaton field, this Gauss-Bonnet term
allows the spectral index of the scalar perturbation spectrum to take values in
the range 0.944 and 0.989, thereby bringing the scenario in closer agreement
with the most recent observations. Once the perturbation spectrum is normalized
to the microwave background temperature anisotropies, the value of the spectral
index is determined by the Gauss-Bonnet coupling parameter and the tension of
the brane and is independent of the logarithmic slope of the potential.


title:
Causality constraints on fluctuations in cosmology: a study with exactly
  solvable one dimensional models

abstract:
  A well known argument in cosmology gives that the power spectrum (or
structure function) $P(k)$ of mass density fluctuations produced from a uniform
initial state by physics which is causal (i.e. moves matter and momentum only
up to a finite scale) has the behaviour $P(k) \propto k^4$ at small $k$. Noting
the assumption of analyticity at $k=0$ of $P(k)$ in the standard derivation of
this result, we introduce a class of solvable one dimensional models which
allows us to study the relation between the behaviour of $P(k)$ at small $k$
and the properties of the probability distribution $f(l)$ for the spatial
extent $l$ of mass and momentum conserving fluctuations. We find that the $k^4$
behaviour is obtained in the case that the first {\it six} moments of $f(l)$
are finite. Interestingly the condition that the fluctuations be localised -
taken to correspond to the convergence of the first two moments of $f(l)$ -
imposes only the weaker constraint $P(k) \propto k^n$ with $n$ anywhere in the
range $0< n \leq 4$. We interpret this result to suggest that the causality
bound will be loosened in this way if quantum fluctuations are permitted.

categories: astro-ph cond-mat.stat-mech hep-ph hep-th


title:
A Rapid Microlensing Event in the Q0957+561 A,B Gravitational Lens
  System

abstract:
  We re-analyze brightness data sampled intensively over 5 nights at two epochs
separated by the quasar lens time delay, to examine the nature of the observed
microlensing. We find strong evidence for a microlensing event with an
amplitude of 1% and a time scale of twelve hours. The existence of such rapid
microlensing, albeit at low amplitude, imposes constraints on the nature of the
quasar and of the baryonic dark matter.


title:
Improved Models of Stellar Core Collapse and Still no Explosions: What
  is Missing?

abstract:
  Two-dimensional hydrodynamic simulations of stellar core-collapse with and
without rotation are presented which for the first time were performed by
solving the Boltzmann equation for the neutrino transport including a
state-of-the-art description of neutrino interactions. Although convection
develops below the neutrinosphere and in the neutrino-heated region behind the
supernova shock, the models do not explode. This suggests missing physics,
possibly with respect to the nuclear equation of state and weak interactions in
the subnuclear regime. However, it might also indicate a fundamental problem of
the neutrino-driven explosion mechanism.


title: On the early evolution of the Galactic Halo

abstract:
  It is shown that the low metallicity tail of the stellar metallicity
distribution predicted by simple Outflow models for the Milky Way halo depends
sensitively on whether Instantaneous Recycling is adopted or relaxed. In both
cases, current - and still preliminary - data suggest a ``G-dwarf problem'' for
the halo (reminiscent of the local disk). We suggest that the problem can be
solved by introducing a (physically motivated) early infall phase. We point out
several important implications of such a modification, concerning: the putative
Pop. III (super)massive stars, the number of stars expected at very low
metallicities, the questions of primary nitrogen and of the dispersion in
abundance ratios of halo stars.


title: Supermassive Black Hole Binaries as Galactic Blenders

abstract:
  This paper focuses on the dynamical implications of close supermassive black
hole binaries both as an example of resonant phase mixing and as a potential
explanation of inversions and other anomalous features observed in the
luminosity profiles of some elliptical galaxies. The presence of a binary
comprised of black holes executing nearly periodic orbits leads to the
possibility of a broad resonant coupling between the black holes and various
stars in the galaxy. This can result in efficient chaotic phase mixing and, in
many cases, systematic increases in the energies of stars and their consequent
transport towards larger radii. Allowing for the presence of a supermassive
black hole binary with plausible parameter values near the center of a
spherical, or nearly spherical, galaxy characterised initially by a Nuker
density profile enables one to reproduce in considerable detail the central
surface brightness distributions of such galaxies as NGC 3706.


title:
The Evolution of a Structured Relativistic Jet and GRB Afterglow
  Light-Curves

abstract:
  We carry out a numerical hydrodynamical modeling for the evolution of a
relativistic collimated outflow, as it interacts with the surrounding medium,
and calculate the light-curve resulting from synchrotron emission of the
shocked fluid. The hydrodynamic equations are reduced to 1-D by assuming axial
symmetry and integrating over the radial profile of the flow, thus considerably
reducing the computation time. We present results for a number of different
initial jet structures, including several different power-laws and a Gaussian
profile for the dependence of the energy per unit solid angle, $\epsilon$, and
the Lorentz factor, $\Gamma$, on the angle from the jet symmetry axis. Our
choice of parameters for the various calculations is motivated by the current
knowledge of relativistic outflows from gamma-ray bursts and the observed
afterglow light-curves. Comparison of the light curves for different jet
profiles with GRB afterglow observations provides constraints on the jet
structure. One of the main results we find is that the transverse fluid
velocity in the comoving frame ($v_t$) and the speed of sideways expansion, for
smooth jet profiles, is typically much smaller than the speed of sound ($c_s$)
throughout much of the evolution of the jet; $v_t$ approaches $c_s$ when
$\Gamma$ along the jet axis becomes of order a few (for large angular gradient
of $\epsilon$, $v_t\sim c_s$ while $\Gamma$ is still large). This result
suggests that the dynamics of relativistic structured jets may be reasonably
described by a simple analytic model where $\epsilon$ is independent of time,
as long as $\Gamma$ along the jet-axis is larger than a few.


title: Large Scale Structure in the Sloan Digital Sky Survey

abstract:
  The primary observational goals of the Sloan Digital Sky Survey are to obtain
CCD imaging of 10,000 deg^2 of the north Galactic cap in five passbands, with a
limiting magnitude in the r-band of 22.5, to obtain spectroscopic redshifts of
10^6 galaxies and 10^5 quasars, and to obtain similar data for three ~ 200
deg^2 stripes in the south Galactic cap, with repeated imaging to allow
co-addition and variability studies in at least one of these stripes. The
resulting photometric and spectroscopic galaxy datasets allow one to map the
large scale structure traced by optical galaxies over a wide range of scales to
unprecedented precision. Results relevant to the large scale structure of our
Universe include: a flat model with a cosmological constant Omega_Lambda=0.7
provides a good description of the data; the galaxy-galaxy correlation function
shows departures from a power law which are statistically significant; and
galaxy clustering is a strong function of galaxy type.


title:
A Comparison of Copper Abundances in Globular Cluster and Halo Field
  Giant Stars

abstract:
  We derive [Cu/Fe] for 117 giant stars in ten globular clusters (M3, M4, M5,
M10, M13, M15, M71, NGC 7006, NCG 288, and NGC 362) and find that globular
cluster Cu abundances appear to follow [Cu/Fe] trends found in the field. This
result is interesting in light of recent work which indicates that the globular
cluster Omega Centauri shows no trend in [Cu/Fe] with [Fe/H] over the abundance
range -2.0 <[Fe/H]< -0.8. Of particular interest are the two clusters M4 and
M5. While at a similar metallicity ([Fe/H] ~- 1.2), they differ greatly in some
elemental abundances: M4 is largely overabundant in Si, Ba, and La compared to
M5. We find that it is also overabundant in Cu with respect to M5, though this
overabundance is in accord with [Cu/Fe] ratios found in the field.


title: Low Statistics of EHECRs

abstract:
  The nature of the unknown sources of ultra-high energy cosmic rays can be
revealed through the detection of the GZK feature in the cosmic ray spectrum.
The only two experiments that have probed this energy range, AGASA and HiRes,
have apparently conflicting results. HiRes measured a flux consistent with the
GZK feature while AGASA reported a larger than expected flux of so-called
Super-GZK particles. Here we emphasize that neither experiment has gathered the
statistics necessary for making a definitive measurement of the GZK cutoff. The
photo-pion production responsible for the GZK feature is stochastic for
energies around the cutoff leading to large fluctuations of the spectrum for
low statistics measurements. We show that the results from AGASA and HiRes
results are within about $ 2 \sigma$ of one another by simulating 400 spectra
for a range of input spectral indices normalized to the number of events above
$10^{19}$ eV for each experiment. If a 15% systematic correction in energy is
applied to both experiments, the agreement between the experiments improves
considerably and the best fit input spectral index becomes $\sim 2.6$ for both
data sets. Our results clearly show the need for much larger experiments such
as Auger and EUSO, that can increase the number of detected events by 2 orders
of magnitude. Only large statistics experiments can finally prove or disprove
the existence of the GZK feature in the cosmic ray spectrum.


title:
An Advanced Analysis Technique for Transient Searches in Wide-Field
  Gamma-Ray Observatories

abstract:
  Wide-field gamma-ray telescopes typically have highly variable event-by-event
resolution which leads to a number of unique and challenging analysis
requirements -- particularly when conducting transient searches over multiple
time scales. By generalizing the ideas of the Gaussian weighting analysis to
point-spread functions of arbitrary shape and the regime of Poisson statistics,
an efficient analysis which uses the event-by-event resolution is developed
with a sensitivity similar to that of a well-implemented maximum likelihood
analysis. In this development, the effect of a number of different
approximations on the sensitivity and speed of the final analysis can be easily
determined and tuned to the particular application. The analysis method is
particularly well suited to transient detection in wide field-of-view gamma-ray
observatories, and is currently used for the 40 s -- 3 hour transient search in
the Milagro observatory.


title: The cosmic production of Helium

abstract:
  We estimate the cosmic production rate of helium relative to metals ($\Delta
Y/\Delta Z$) using K dwarf stars in the Hipparcos catalog with accurate
spectroscopic metallicities. The best fitting value is $\Delta Y/\Delta Z=2.1
\pm 0.4$ at the 68% confidence level. Our derived value agrees with
determinations from HII regions and with theoretical predictions from stellar
yields with standard assumptions for the initial mass function. The amount of
helium in stars determines how long they live and therefore how fast they will
enrich the insterstellar medium with fresh material.


title: Precision Cosmology? Not Just Yet

abstract:
  The recent announcement from the Wilkinson Microwave Anisotropy Probe (WMAP)
satellite experiment combined with other recent advances in observational
cosmology verifies key components of the standard cosmological model. However,
we argue that there remain some significant open issues regarding the basic
history and composition of the Universe and uncertainties in some of the most
important parameters.


title: The Luminosity Function of IRAS PSCz Galaxies

abstract:
  We estimated the luminosity function (LF) of IRAS galaxies in the PSCz
catalogue. The faint end of the PSCz LF is slightly steeper than that of the LF
derived by Saunders et al. (1990; S90). Using an analytical form for the LF
used by S90, we obtain the following parameters: \alpha = 1.23 \pm 0.04,
L_*=(8.85 \pm 1.75) \times 10^8 h^{-2} L_\odot, \sigma =0.724 \pm 0.010, and
\phi_* = (2.34 \pm 0.30) \times 10^{-2} h^3 Mpc^{-3}. We also examined the
evolution in the sample by a simple assumption \phi_*(z) \propto (1+z)^P, and
found P=3.40 \pm 0.70. It does not affect the three parameters, \alpha, L_*,
and \sigma, but \phi_*(z=0) is overestimated up to \sim 15% if we ignore
evolution. We estimated the temperature dependence of the LF. The LFs of warm
and cool galaxies are quite different: the LF of warm galaxies has a very steep
faint end with \alpha =1.37. We also discuss a lump found at the brightest end
of the LF.


title:
Equation of Motion for an Arbitrarily Shaped Particle Moving in a
  Radiation Field

abstract:
  We consider the motion of uncharged dust grains of arbitrary shape including
the effects of electromagnetic radiation and thermal emission. The resulting
relativistically covariant equation of motion is expressed in terms of standard
optical parameters. Explicit expressions for secular changes of osculating
orbital elements are derived in detail for the special case of the
Poynting-Robertson effect. Two subcases are considered: (i) central
acceleration due to gravity and the radial component of radiation pressure
independent of the particle velocity, (ii) central acceleration given by
gravity and the radiation force as the disturbing force. The latter case yields
results which may be compared with secular orbital evolution in terms of
orbital elements for an arbitrarily shaped dust particle. The effects of solar
wind are also presented.