title: Very High Energy Gamma Ray Emission from Crab Nebula with the PACT Array

abstract:
  The Crab nebula has proved to be the nearest to a standard candle in VHE
$\gamma-$ ray astronomy. Results on the gamma ray emission from the nebula at
various energies have come in the last decade mostly from imaging telescopes.
The aim of the new Pachmarhi Atmospheric Cerenkov Telescope (PACT) array has
been to use the temporal and spatial distribution of Cerenkov photons in
distinguishing between proton and gamma ray showers. The array, with timing
information from 175 mirrors, is ideally suited for precise estimation of the
arrival direction. Preliminary results from the recent data taken on Crab has
shown a 12$\sigma$ signal with the flux in good agreement with those of the
other experiments.


title:
Thunderclouds and accretion discs: a model for the spectral and temporal
  variability of Seyfert 1 galaxies

abstract:
  X-ray observations of Seyfert 1 galaxies offer the unique possibility of
observing spectral variability on timescales comparable to the dynamical time
of the inner accretion flow. They typically show highly variable lightcurves,
with Power Density Spectra characterized by `red noise' and a break at low
frequencies. Time resolved spectral analysis have established that spectral
variability on the shortest timescales is important in all these sources, with
the spectra getting softer at high fluxes. Here we present a model that is able
to explain a number of the above mentioned properties in terms of magnetic
flares shining above a standard accretion disc and producing the X-ray spectrum
via inverse Compton scattering soft photons (both intrinsic and reprocessed
thermal emission from the accretion disc and locally produced synchrotron
radiation). We show that the fundamental heating event, likely caused by
magnetic reconnection, must be compact, with typical size comparable to the
accretion disc thickness and must be triggered at a height at least an order of
magnitude larger than its size; the spatial and temporal distribution of flares
are not random: the heating of the corona proceeds in correlated trains of
events in an avalanche fashion. The amplitude of the avalanches obeys a
power-law distribution and determines the size of the active regions where the
spectrum is produced. With our model we simulate X-ray lightcurves that
reproduce the main observational properties of the Power Density Spectra and of
the X-ray continuum short-term variability of Seyfert 1 galaxies. By comparing
them with observations of MGC--6-30-15, we are able to infer that the corona in
this source must have a large optical depth (tau >1.5) and small average
covering fraction.


title: Are there sextuplet and octuplet image systems?

abstract:
  We study gravitational lensing by the family of scale-free galaxies with flat
rotation curves. The models are defined by a shape function, which prescribes
the radius of the isophote as a function of position angle from the major axis.
The critical curves are analytic, while the caustic network is reducible to a
simple quadrature. The cusps are always located at the turning points of the
shape function. We show that the models with exactly elliptic isophotes never
admit butterfly or swallowtail cusps and so have at most 4 (or 5) images.
Higher order imaging is brought about by deviations of the isophotes from pure
ellipses -- such as pointedness caused by embedded disks or boxiness caused by
recent merging. The criteria for the onset of sextuple and octuple imaging can
be calculated analytically in terms of the ellipticity and the fourth-order
Fourier coefficients (a_4 and b_4) used by observers to parametrise the
isophote shapes. The 6 or 8 images are arranged roughly in a circle, which
appears as an incomplete Einstein ring if inadequately resolved. Using data on
the shapes of elliptical galaxies and merger remnants, we estimate that 1% of
all multiply imaged quasars may be sextuplet systems or higher. Forthcoming
satellites like the Global Astrometric Interferometer for Astrophysics (GAIA)
will provide datasets of roughly 4000 multiply imaged systems, and so about 40
will show sextuple imaging or higher.


title:
Submillimeter lines from circumstellar disks around pre-main sequence
  stars

abstract:
  Observations of submillimeter lines of CO (up to J=6-5), HCO+, HCN (up to
J=4-3) and their isotopes from circumstellar disks around low mass pre-main
sequence stars are presented. The different line ratios and optical depths
indicate that most of the observed line emission arises from an intermediate
disk layer with high densities of 1E6-1E8 cm-3 and moderately warm temperatures
in the outer regions. The data are compared with three disk models from the
literature using a full 2D Monte Carlo radiative transfer code. The abundances
of the molecules are constrained from the more optically thin 13C species and
indicate depletions of 1-30 for LkCa 15 and very high depletions of > 100 for
TW Hya with respect to dark cloud abundances. Evidence for significant
freeze-out (factors 10 or larger) of CO and HCO+ onto grain surfaces at
temperatures below 22 K is found, but the abundances of these molecules must
also be low in the warmer upper layer, most likely as a result of
photodissociation. A warm upper layer near the surface of a flaring disk heated
by stellar and interstellar radiation is an appropriate description of the
observations of TW Hya. LkCa 15 seems to be cooler at the surface, perhaps due
to dust settling.


abstract:
  The ASCA satellite made 107 pointing observations on a 5 x 5 deg^2 region
around the center of our Milky Way Galaxy (the Galactic Center) from 1993 to
1999. In the X-ray images of the 0.7--3 keV or 3--10 keV bands, we found 52
point sources and a dozen diffuse sources. All the point sources are uniformly
fitted with an absorbed power-law model. For selected bright sources, Sgr A*,
AX J1745.6-2901, A 1742-294, SLX 1744-300, GRO J1744-28, SLX 1737-282, GRS
1734-292, AX J1749.2-2725, KS 1741-293, GRS 1741.9-2853, and an unusual flare
source XTE J1739-302, we present further detailed spectral and timing analyses,
and discuss their nature.
  The dozen extended X-ray sources comprise radio supernova remnants, giant
molecular clouds, and some new discoveries. Most show emission lines from
either highly ionized atoms or low-ionized irons.
  The X-ray spectra were fitted with either a thin thermal or power-law model.
This paper summarizes the results and provides the ASCA X-ray source catalogue
in the Galactic Center region.


title: RX J1643.7+3402 : a new bright cataclysmic variable

abstract:
  We report the discovery of a new bright (V$\sim$12.6) cataclysmic variable
star identified with the ROSAT X-ray source RX J1643.7+3402. Spectroscopic and
photometric observations show it to be a novalike variable sharing some of the
characteristics of the SW Sex sub-class of novalike CVs. The spectroscopic
period may be either 2\fh575 or 2\fh885, within the period "gap." A photometric
modulation with a probable period of 2\fh595 and an amplitude of $\sim$ 0.1 mag
in V is present on most nights and could be either a "positive" or a "negative"
superhump modulation (depending on the exact spectroscopic period), indicating
the presence of a precessing accretion disk in this system. Rapid variations of
0.1 to 0.2 mag amplitude in V repeat with a time scale of $\sim$ 15 min.


title:
Gravitational instability of polytropic spheres and generalized
  thermodynamics

abstract:
  We complete the existing literature on the structure and stability of
polytropic gas spheres reported in the classical monograph of Chandrasekhar
(1942). For isolated polytropes with index $1<n<5$, we provide a new,
alternative, proof that the onset of instability occurs for $n=3$ and we
express the perturbation profiles of density and velocity at the point of
marginal stability in terms of the Milne variables. Then, we consider the case
of polytropes confined within a box of radius $R$ (an extension of the Antonov
problem for isothermal gas spheres). For $n\ge 3$, the mass-density relation
presents some damped oscillations and there exists a limiting mass above which
no hydrostatic equilibrium is possible. Like for isothermal gas spheres, the
onset of instability occurs precisely at the point of maximum mass. Analytical
results are obtained for the particular index $n=5$. We also discuss the
relation of our study with extended thermodynamics (Tsallis entropy) recently
investigated by Taruya & Sakagami (cond-mat/0107494).


title:
A Single Distance Sample of Molecular Outflows from High-Mass Young
  Stellar Objects

abstract:
  We have made 12CO 2-1 and 1-0 maps of eleven molecular outflows associated
with intermediate to high-mass young stellar objects (YSOs) in order to
establish whether the correlations between outflow parameters and source
bolometric luminosity hold in the high-mass regime. It is important to consider
the effects of Malmquist-type biases when looking at high-mass YSOs, as they
are generally much more distant than their low mass counterparts. We therefore
chose only objects located at ~2kpc. We find that the relations show much more
scatter than is seen in similar studies of low-mass YSOs. We also find that the
mass-spectrum is significantly steeper in high-mass outflows, indicating a
larger mass-fraction at lower velocities, a low collimation factor (~1-2) and
no Hubble-like relationship.


title: Panchromatic Mining for Quasars: An NVO Keystone Science Application

abstract:
  A data Tsunami is overwhelming Astronomy. This wave is affecting all aspects
of our field, revolutionizing not just the type of scientific questions being
asked, but the very nature of how the answers are uncovered. In this invited
proceeding, we will address a particular scientific application - Panchromatic
Mining for Quasars - of the forthcoming virtual observatories, which have
arisen in an effort to control the effects of the data Tsunami. This project,
in addition to serving as an important scientific driver for virtual
observatory technologies, is designed to a) characterize the multi-wavelength
nature of known active galaxies and quasars, especially in relation to their
local environment, in order to b) quantify the clustering of these known
systems in the multidimensional parameter space formed by their observables, so
that new, and potentially unknown types of systems can be optimally targeted.


title: The National Virtual Observatory

abstract:
  As a scientific discipline, Astronomy is rather unique. We only have one
laboratory, the Universe, and we cannot, of course, change the initial
conditions and study the resulting effects. On top of this, acquiring
Astronomical data has historically been a very labor-intensive effort. As a
result, data has traditionally been preserved for posterity. With recent
technological advances, however, the rate at which we acquire new data has
grown exponentially, which has generated a Data Tsunami, whose wave train
threatens to overwhelm the field. In this conference proceedings, we present
and define the concept of virtual observatories, which we feel is the only
logical answer to this dilemma.


title: HD 12098 - A new norhtern hemisphere roAp star

abstract:
  We present the analysis of 65 hours of high speed photometric observations of
HD 12098 taken from State Observatory, Naini Tal and Gurushikhar Observatory,
Mt.Abu on sixteen nights spanning from November 1999 to November 2000. HD 12098
is the first rapidly oscillating Ap star discovered from the `Naini Tal-Cape
survey for northern hemisphere roAp stars'. It is the 32nd in the complete
list. HD 12098 exhibits one predominant mode of oscillation at nu_1 = 2.1738
mHz. The second-most significant frequency in our data is at nu_2 = 2.1641 mHz
with a 1 cycle/day alias ambiguity. We argue that nu_2 is a rotational sidelobe
of nu_1, rather than an independent pulsation mode. Evidence for the presence
of two other frequencies at 2.1807 and 2.3056 mHz is also presented.


title: PG 1254+047: An Intrinsically X-ray Weak, Heavily Absorbed BALQSO?

abstract:
  We present \textit{Chandra} observations of the radio-quiet Broad Absorption
Line (BAL) QSO PG 1254+047. We find that it is a weak X-ray source, with a
total of $44\pm 7$ photons measured in 36 ksec across the observed energy range
$0.7 - 6.0$ keV. Its X-ray weakness is consistent with the known correlation
between $\alpha_{ox}$ and the strength of the UV absorption lines. The spectral
energy distribution suggests that PG 1254+047 is intrinsically X-ray weak, in
addition to being heavily X-ray absorbed. The X-ray absorption column density
is $N_{H} > 10^{23}$ cm$^{-2}$ for neutral gas, while the intrinsic
(unabsorbed) emission spectrum has $\alpha_{ox} > 2$. The data are fit best by
including an ionized (rather than neutral) absorber, with column density $N_{H}
\gtrsim 2\times 10^{23}$ cm$^{-2}$. The degree of ionization is consistent with
the UV BALs, as is the total column density if the strongest UV lines are
saturated. If the X-ray absorber forms in a wind that is radiatively
accelerated to the BAL velocities, then the wind must be launched from a radius
of about $10^{16}$ cm with a mass loss rate of $\sim 1$ M$_\odot$ yr$^{-1}$.


title: Angular Resolution of Pachmarhi Array of Cerenkov Telescopes

abstract:
  Pachmarhi Array of \v{C}erenkov Telescopes(PACT), consisting of a distributed
array of 25 telescopes is used to sample the atmospheric \v{C}erenkov Photon
showers. The shower front is fitted to a plane and the direction of arrival of
primary particle is obtained. The accuracy in the estimation of the arrival
direction of showers has been estimated to be $\sim 0^{\circ}.1~$ using `split'
array method. The angular resolution is expected to be even better when a
spherical front is used for direction reconstruction or correction for the
curvature of the front is applied. This is the best angular resolution among
all the currently operating atmospheric \v{C}erenkov telescopes in the world.


title: Very High Energy Gamma Ray Emission from Crab and Geminga Pulsars

abstract:
  The main inference from the experiments of the '80s that the time-averaged
energy spectra of pulsars had to steepen in the GeV-TeV energy region has been
reinforced in the '90s from experiments with higher sensitivities. However,
results from several experiments from the past and the more sensitive
experiments at present can be reconciled by invoking a possibly different
component arising in the TeV region. The results of the preliminary analysis of
the data being collected with the PACT array will be presented.


title:
Hubble Space Telescope Spectroscopy of V471 Tauri: Oversized K Star,
  Paradoxical White Dwarf

abstract:
  We have used the GHRS onboard the HST to obtain Lyman-alpha spectra of the
hot white-dwarf (WD) component of the short-period eclipsing DA+dK2
pre-cataclysmic binary V471 Tauri, a member of the Hyades star cluster. Radial
velocities of the WD, combined with ground-based measurements of the dK
velocities, eclipse timings, and a determination of the dK star's rotational
velocity, yield dynamical masses for the components of M(WD)=0.84 and
M(dK)=0.93 Msun. Model-atmosphere fitting of the Ly-alpha profile provides the
effective temperature (34,500 K) and surface gravity (log g=8.3) of the WD. The
radius of the dK component is 18% larger than that of a normal Hyades dwarf of
the same mass. This expansion is attributed to the extensive coverage of the
surface by starspots, causing the star to expand in response. The WD radius,
determined from a radiometric analysis and from eclipse ingress timings, is
0.0107 Rsun. The position of the star in the M-R plane is in full accord with
theory for a degenerate CO WD. The high temperature and mass of the WD present
an evolutionary paradox: the WD is the most massive known in the Hyades, but
also the hottest and youngest. We suggest that the explanation is that the WD
is indeed very young, and is descended from a triple consisting of a blue
straggler and a more-distant dK companion. We estimate that the common-envelope
efficiency parameter, alpha_CE, was of order 0.3-1.0, in good agreement with
recent hydrodynamical simulations.


title:
X-ray Spectral Variability and Rapid Variability of the Soft X-ray
  Spectrum Seyfert 1 Galaxies Ark 564 and Ton S180

abstract:
  The bright, soft X-ray spectrum Seyfert 1 galaxies Ark 564 and Ton S180 were
monitored for 35 days and 12 days with ASCA and RXTE (and EUVE for Ton S180).
The short time scale (hours-days) variability patterns were very similar across
energy bands, with no evidence of lags between any of the energy bands studied.
The fractional variability amplitude was almost independent of energy band. It
is difficult to simultaneously explain soft Seyferts stronger variability,
softer spectra, and weaker energy-dependence of the variability relative to
hard Seyferts. The soft and hard band light curves diverged on the longest time
scales probed, consistent with the fluctuation power density spectra that
showed relatively greater power on long time scales in the softest bands. The
simplest explanation is that a relatively hard, rapidly-variable component
dominates the total X-ray spectrum and a slowly-variable soft excess is present
in the lowest energy channels of ASCA. Although it would be natural to identify
the latter with an accretion disk and the former with a corona surrounding it,
a standard thin disk could not get hot enough to radiate significantly in the
ASCA band, and the observed variability time scales are much too short. The
hard component may have a more complex shape than a pure power-law. The most
rapid factor of 2 flares and dips occurred within ~1000 sec in Ark 564 and a
bit more slowly in Ton S180. The speed of the luminosity changes rules out
viscous or thermal processes and limits the size of the individual emission
regions to <~15 Schwarzschild radii (and probably much less), that is, to
either the inner disk or small regions in a corona.


title:
Intra-Cluster Medium Enrichment and the Dynamical State of Galaxy
  Clusters

abstract:
  The effects of cluster mergers on the metal enrichment of the intra-cluster
gas in clusters of galaxies are reviewed. Mergers can influence the metal
production as well as the gas ejection processes, which transport the gas from
the galaxy potential wells into the intra-cluster gas. Several processes are
discussed: ram-pressure stripping, galactic winds and star formation activity.
Simulations on different scales ranging from galaxy size to large-scale
structure are presented.


title:
The fraction of galaxies that contain active nuclei and their accretion
  rates

abstract:
  We investigate the relationship between the present day optical luminosity
function of galaxies and the X-ray luminosity function of Seyfert 1s to
determine the fraction of galaxies which host Seyfert 1 nuclei and their
Eddington ratios. The local type 1 AGN X-ray luminosity function is well
reproduced if ~ 1% of all galaxies are type 1 Seyferts which have Eddington
ratios of ~ 10^{-3}. However, in such a model the X-ray luminosity function is
completely dominated by AGN in E and S0 galaxies, contrary to the observed mix
of Seyfert host galaxies. To obtain a plausible mix of AGN host galaxy
morphologies requires that the most massive black holes in E and S0 galaxies
accrete with lower Eddington ratios, or have a lower incidence of Seyfert
activity, than the central black holes of later type galaxies.


title: Estimation of Shower Parameters in Wavefront Sampling Technique

abstract:
  Wavefront sampling experiments record arrival times of \v{C}erenkov photons
with high precision at various locations in \v{C}erenkov pool using a
distributed array of telescopes. It was shown earlier that this photon front
can be fitted with a spherical surface traveling at a speed of light and
originating from a single point on the shower axis. Radius of curvature of the
spherical shower front ($R$) is approximately equal to the height of shower
maximum from observation level. For a given primary species, it is also found
that $R$ varies with the primary energy ($E$) and this provides a method of
estimating the primary energy. In general, one can estimate the arrival times
at each telescope using the radius of curvature, arrival direction of the
primary and the core location. This, when compared with the data enables us to
estimate the above parameters for each shower. This method of obtaining the
arrival direction alleviates the difficulty in the form of systematics arising
out of the plane wavefront approximation for the \v{C}erenkov front. Another
outstanding problem in the field of atmospheric \v{C}erenkov technique is the
difficulty in locating the shower core. This method seems to solve both these
problems and provides an elegant method to determine the arrival direction as
well as the core location from timing information alone. In addition, using the
\v{C}erenkov photon density information and the core position we can estimate
the energy of the primary if the nature of the primary is known. Combining
these two independent estimates of the primary energy, the energy resolution
can be further improved. Application of this methodology to simulated data and
the results will be presented. The intrinsic uncertainties on the various
estimated parameters also will be discussed.


title: Gamma-Hadron Separation using \v{C}erenkov Photon Density Fluctuations

abstract:
  In atmospheric \v{C}erenkov technique $\gamma-$rays are detected against
abundant background produced by hadronic showers. In order to improve signal to
noise ratio of the experiment, it is necessary to reject a significant fraction
of hadronic showers. The temporal and spectral differences, the lateral
distributions and density fluctuations of \v{C}erenkov photons generated by
$\gamma-$ray and hadron primaries are often used for this purpose. Here we
study the differences in \v{C}erenkov photon density fluctuations at the
observation level based on Monte Carlo simulations. Various types of density
fluctuations like the short range (or local), medium range fluctuations and
flatness parameter are studied. The estimated quality factors reflect the
efficiencies with which the hadrons can be rejected from the data. It has been
found that we can reject around 80% of proton showers while retaining about 70%
of $\gamma-$ray showers in the data, based only on the differences in the
flatness parameter. Density fluctuations particularly suited for wavefront
sampling observations seem to be a good technique to improve the signal to
noise ratio.


title: A Possible High Altitude High Energy Gamma Ray Observatory in India

abstract:
  Recently an Indian Astronomical Observatory has been set up at Hanle
(32$^\circ$ 46$^\prime$ 46$^{\prime\prime}$ N, 78$^\circ$ 57$^\prime$
51$^{\prime\prime}$ E, 4515m amsl) situated in the high altitude cold desert in
the Himalayas. The Observatory has 2-m aperture optical-infrared telescope,
recently built by the Indian Institute of Astrophysics.
  We have carried out systematic simulations for this observation level to
study the nature of \v{C}erenkov light pool generated by gamma ray and proton
primaries incident vertically at the top of the atmosphere. The differences in
the shape of the lateral distributions of \v{C}erenkov light with respect to
that at lower altitudes is striking. This arises primarily due to the proximity
of the shower maximum to the observation site. The limited lateral spread of
the \v{C}erenkov light pool and near 90% atmospheric transmission at this high
altitude location makes it an ideal site for a gamma ray observatory. This
results in a decrease in the gamma ray energy threshold by a factor of 2.9
compared to that at sea-level. Several parameters based on density and timing
information of \v{C}erenkov photons, including local and medium range photon
density fluctuations as well as photon arrival time jitter could be efficiently
used to discriminate gamma rays from more abundant cosmic rays at tens of GeV
energies.


title: Lateral Distribution Studies for the PACT Experiment

abstract:
  Monte Carlo calculations have been done to study the possibilities of using
different spatial distributions, local fluctuations and the number of Cerenkov
photons in gamma ray showers to increase the sensitivity of the PACT
experiment. After matching the trigger rates in data with the predictions of
simulations, the energy threshold of the array for gamma rays is found to be
about 900 GeV. It is shown that a lateral distribution parameter $\beta$ can
increase the signal to noise ratio in the experiment. A typical season of 15
nights should be able to conclusively establish any source with Crab level
fluxes. Two other possible parameters for increase of sensitivity are also
discussed. Preliminary results on the application of the $\beta$ parameter to
the data from PACT experiment are discussed.


title: A catalogue of AGN observed by the PDS experiment on board BeppoSAX

abstract:
  The PDS experiment onboard BeppoSAX is the most sensitive instrument ever
above 10 keV. Preliminary results on the complete catalogue of AGN observed
with it are presented in this paper.


title:
Chemical Abundances of OB Stars with High Projected Rotational
  Velocities

abstract:
  Elemental abundances of carbon, nitrogen, oxygen, magnesium, aluminum, and
silicon are presented for a sample of twelve rapidly rotating OB star (v sin i
> 60 km s^-1) members of the Cep OB2, Cyg OB3 and Cyg OB7 associations. The
abundances are derived from spectrum synthesis, using both LTE and non-LTE
calculations. As found in almost all previous studies of OB stars, the average
abundances are slightly below solar, by about 0.1 to 0.3 dex. In the case of
oxygen, even with the recently derived low solar abundances the OB stars are
closer to, but still below, the solar value. Results for the 9 Cep OB2 members
in this sample can be combined with results published previously for 8 Cep OB2
stars with low projected rotational velocities to yield the most complete set
of abundances, to date, for this particular association. These abundances
provide a clear picture of both the general chemical and individual stellar
evolution that has occurred within this association. By placing the Cep OB2
stars studied in an HR diagram we identify the presence of two distinct age
subgroups, with both subgroups having quite uniform chemical abundances. Two
stars are found in the older subgroup that show significant N/O overabundances,
with both stars being two of the most massive, the most evolved, and most
rapidly rotating of the members studied in Cep OB2. These characteristics of
increased N abundances being tied to high mass, rapid rotation, and an evolved
phase are those predicted from models of rotating stars which undergo
rotationally driven mixing.


title: The Small-scale Structure of N103B - Nature of Nuture?

abstract:
  We present new results from a 40.8 ks Chandra ACIS observation of the young
supernova remnant (SNR) N103B located in the Large Magellanic Cloud. The high
resolution Chandra image reveals structure at the sub-arcsecond level,
including several bright knots and filaments. Narrow-band imaging and spatially
resolved spectroscopy reveal dramatic spectral variations in this remnant as
well. In this paper we discuss whether these variations are due to
inhomogeneities in the surrounding environment or were generated in the
explosion which created the SNR.


title: Quasars, their host galaxies, and their central black holes

abstract:
  We present the final results from our deep HST imaging study of the hosts of
radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and radio galaxies (RGs).
We describe new WFPC2 R-band observations for 14 objects and model these images
in conjunction with the data already reported in McLure et al (1999). We find
that spheroidal hosts become more prevalent with increasing nuclear luminosity
such that, for nuclear luminosities M_V < -23.5, the hosts of both radio-loud
and radio-quiet AGN are virtually all massive ellipticals. Moreover we
demonstrate that the basic properties of these hosts are indistinguishable from
those of quiescent, evolved, low-redshift ellipticals of comparable mass. This
result kills any lingering notion that radio-loudness is determined by
host-galaxy morphology, and also sets severe constraints on evolutionary
schemes which attempt to link low-z ULIRGs with RQQs. Instead, we show that our
results are as expected given the relationship between black-hole and spheroid
mass established for nearby galaxies, and apply this relation to estimate the
mass of the black hole in each object. The results agree very well with
completely-independent estimates based on nuclear emission-line widths; all the
quasars in our sample have M(bh) > 5 x 10^8 solar masses, while the radio-loud
objects are confined to M(bh) > 10^9 solar masses. This apparent mass-threshold
difference, which provides a natural explanation for why RQQs outnumber RLQs by
a factor of 10, appears to reflect the existence of a minimum and maximum level
of black-hole radio output which is a strong function of black-hole mass.
Finally, we use our results to estimate the fraction of massive
spheroids/black-holes which produce quasar-level activity. This fraction is
\~0.1% at the present day, rising to > 10% at z = 2-3.


title: X-ray transient AGN and galaxies

abstract:
  X-ray transience is the most extreme form of variability observed in AGN or
normal in-active galaxies. While factors of 2-3 on timescales of days to years
are quite commen among AGN, X-ray transients appear only once and vanish from
the X-ray sky years later. The ROSAT All-Sky Survey was the tool to discover
these sources. X-ray transience in AGN or galaxies can be caused by dramatic
changes in the accretion rate of the central black hole or by changes of the
properties of the accretion disk.


title: Lens magnification by CL0024+1654 in the U and R band

abstract:
  [ABRIDGED] We estimate the total mass distribution of the galaxy cluster
CL0024+1654 from the measured source depletion due to lens magnification in the
R band. Within a radius of 0.54Mpc/h, a total projected mass of
(8.1+/-3.2)*10^14 M_sol/h (EdS) is measured, which corresponds to a mass-
to-light ratio of M/L(B)=470+/-180. We compute the luminosity function of
CL0024+1654 in order to estimate contamination of the background source counts
from cluster galaxies. Three different magnification-based reconstruction
methods are employed using both local and non-local techniques. We have
modified the standard single power-law slope number count theory to incorporate
a break and applied this to our observations. Fitting analytical magnification
profiles of different cluster models to the observed number counts, we find
that the cluster is best described either by a NFW model with scale radius
r_s=334+/-191 kpc/h and normalisation kappa_s=0.23+/-0.08 or a power-law
profile with slope xi=0.61+/-0.11, central surface mass density
kappa_0=1.52+/-0.20 and assuming a core radius of r_core=35 kpc/h. The NFW
model predicts that the cumulative projected mass contained within a radius R
scales as M(<R)=2.9*10^14*(R/1')^[1.3-0.5lg (R/1')] M_sol/h. Finally, we have
exploited the fact that flux magnification effectively enables us to probe
deeper than the physical limiting magnitude of our observations in searching
for a change of slope in the U band number counts. We rule out both a total
flattening of the counts with a break up to U_AB<=26.6 and a change of slope,
reported by some studies, from dlog N/dm=0.4->0.15 up to U_AB<=26.4 with 95%
confidence.


title: The coincidence and angular clustering of Chandra and SCUBA sources

abstract:
  We explore the relationship between the hard X-ray and sub-mm populations
using deep Chandra observations of a large, contiguous SCUBA survey. In
agreement with other recent findings, we confirm that the direct overlap is
small. Of the 17 sub-mm sources detected in this field at 850 microns, only one
is coincident with a Chandra source. The resulting limits imply that the
majority of SCUBA sources are not powered by AGN, unless the central engine is
obscured by Compton-thick material with a low (<1 per cent) scattered
component. Furthermore, since Chandra detects only ~5 per cent of SCUBA
sources, the typical obscuration would need to be almost isotropic. The X-ray
upper limits are so strong that in most cases we can also rule out a starburst
SED at low redshift, suggesting that the majority of SCUBA sources lie at z>1
even if they are purely starburst galaxies. Despite the low detection rate, we
find evidence for strong angular clustering between the X-ray and sub-mm
populations. The implication is that AGN and SCUBA sources trace the same
large-scale structure but do not generally coincide. If bright sub-mm sources
represent massive elliptical galaxies in formation, we suggest that (for a
given galaxy) the major episode of star-formation must be distinct from the
period of observable quasar activity.


title:
Galactic Magnetic Field Structure and Ultra High Energy Cosmic Ray
  Propagation

abstract:
  We consider the effects of the Galactic magnetic field on the propagation of
ultra high energy cosmic rays (UHECRs). By employing two methods of trajectory
simulation, we investigate the possibility that UHECRs are produced within the
Galaxy with paths strongly influenced by the Galactic magnetic field. Such
trajectories have the potential to reconcile the existing conflict between
proposed local sources and isotropic UHECR arrival directions.


title:
Gamma-ray bursts with continuous energy injection and their afterglow
  signature

abstract:
  (Abridged) We discuss a Gamma-ray burst (GRB) fireball with an additional
energy injection, either in the form of a Poynting-flux-dominated outflow or a
kinetic-energy-dominated matter shell injected after the burst. A total
injection energy comparable to that of the impulsive energy in the initial
fireball is required to make a detectable signature in the afterglow
lightcurves. For the case of a Poynting-flux-dominated injection, this leads to
a gradual achromatic bump feature. For the case when the injection is
kinetic-energy-dominated, the collision between the rear (injected) and the
forward shell mild if the relative velocity between the colliding shells does
not exceed a critical value defined by their energy ratio. Otherwise, the
injection is violent, and an additional pair of shocks will form at the
discontinuity between two colliding shells, so that there are altogether three
shock-heated regions from which the emission contributes to the final
lightcurves. We describe the shell-merging process in detail and present
broadband lightcurves with the injection signatures. A violent collision
results in very complicated features, which differs from the gradual bump
signature found in the Poynting-flux or mild matter injection cases. In all the
cases, the energetics of the fireball as well as the absolute afterglow flux
level after the injection are boosted after the injection. Identifying the
different injection signatures from future early afterglow observations may
provide diagnostics about the nature of the fireball and of the central engine.


title:
A Complete Analytic Inversion of Supernova Lines in the Sobolev
  Approximation

abstract:
  We show that the shape of P-Cygni line profiles of photospheric phase
supernova can be analytically inverted to extract both the optical depth and
source function of the line -- i.e. all the physical content of the model for
the case when the Sobolev approximation is valid. Under various simplifying
assumptions, we derive formulae that give S(r) and tau(r) in terms of
derivatives of the line flux with respect to wavelength. The transition region
between the minimum and maximum of the line profile turns out to give
especially interesting information on the optical depth near the photosphere.
The formulae give insights into the relationship between line shape and
physical quantities that may be useful in interpreting observed spectra and
detailed numerical calculations.


title: The Chandra Deep Field North Survey. V. 1 Ms Source Catalogs

abstract:
  An extremely deep X-ray survey (about 1 Ms) of the Hubble Deep Field North
and its environs (about 450 arcmin^2) has been performed with the Advanced CCD
Imaging Spectrometer on board the Chandra X-ray Observatory. This is one of the
two deepest X-ray surveys ever performed; for point sources near the aim point
it reaches 0.5-2.0 keV and 2-8 keV flux limits of 3 x 10^{-17} erg/cm^2/s and 2
x 10^{-16} erg/cm^2/s, respectively. Here we provide source catalogs along with
details of the observations, data reduction, and technical analysis. Observing
conditions, such as background, were excellent for almost all of the exposure.
We have detected 370 distinct point sources: 360 in the 0.5-8.0 keV band, 325
in the 0.5-2.0 keV band, 265 in the 2-8 keV band, and 145 in the 4-8 keV band.
Two new Chandra sources in the HDF-N itself are reported and discussed. Source
positions are accurate to within 0.6-1.7 arcsec (at 90% confidence) depending
mainly on the off-axis angle. We also detect two highly significant extended
X-ray sources and several other likely extended X-ray sources. We present basic
number count results for sources located near the center of the field. Source
densities of 7100^{+1100}_{-940} deg^{-2} (at 4.2 x 10^{-17} erg/cm^2/s) and
4200^{+670}_{-580} deg^{-2} (at 3.8 x 10^{-16} erg/cm^2/s) are observed in the
soft and hard bands, respectively.


title: Binary and Long-Term (Triple?) Modulations of 4U 1820$-$30 in NGC 6624

abstract:
  We present timing analysis results for Rossi x-ray Timing Explorer (RXTE)
observations of x-ray binary source 4U 1820$-$30 located in the globular
cluster NGC 6624. The light curves of observations made between October 1996
and September 1997 show that the maximum of the 685s binary period modulation
folded by the linear ephemeris from previous observations has phase shift of
$-$0.20 $\pm$ 0.06. Combined with historical results (1976-1997), the binary
period derivative is measured to be $\dot P / P =(-3.47 \pm 1.48) \times
10^{-8}$ yr$^{-1}$. The previous known ($\sim$176 d) long-term modulation is
significant in the x-ray light curve obtained by analysis of the RXTE All-Sky
Monitor (ASM) during the years 1996-2000. The RXTE/ASM ephemeris is extended by
analysis of all historical data (Vela 5B and Ginga) to yield a period
171.033$\pm$0.326 days with no evidence for period change ($|{\dot{P}/ {P}}| <
2.20 \times 10^{-4}$ yr$^{-1}$). All reported x-ray burst activity is confined
to within $\pm$23 d of the predicted minima. This stable long-term modulation
is consistent with 4U 1820$-$30 being a hierarchical triple system with a
$\sim$1.1 d period companion.


title: Origin of the Hard X-ray Emission from the Galactic Plane

abstract:
  The Galactic plane is a strong hard x-ray emitter and the emission forms a
narrow continuous ridge. The currently known hard x-ray sources are far too few
to explain the ridge x-ray emission, and the fundamental question as to whether
the ridge emission is ultimately resolved into numerous dimmer discrete sources
or truly diffuse emission has not yet been settled. In order to obtain a
decisive answer, using the Chandra x-ray observatory, we have carried out the
deepest hard x-ray survey of a Galactic plane region which is devoid of known
x-ray point sources. We have detected at least 36 new hard x-ray point sources
in addition to strong diffuse emission within a 17' x 17' field of view. The
surface density of the point sources is comparable to that at high Galactic
latitudes after the effects of Galactic absorption are considered. Therefore,
most of these point sources are probably extragalactic, presumably active
galaxies seen through the Galactic disk. The Galactic ridge hard x-ray emission
is diffuse, which indicates omnipresence of the hot plasma along the Galactic
plane whose energy density is more than one order of magnitude higher than any
other substances in the interstellar space.


title:
Period Changes of the LMC Cepheids Determined from the Harvard, OGLE and
  ASAS Data

abstract:
  Observations of Cepheids in the Large Magellanic Cloud, made over the last
several decades, allow us to search for evolutionary period changes. None of
the Cepheid from our sample of 378 stars stopped pulsating. Also none of them
showed a large period change which could indicate mode switching. However for
Cepheids with log P > 0.9 we found significant period changes, positive as well
as negative. A comparison between the observed period changes and theoretical
predictions shows moderate agreement with some models (Bono et al. 2000), and a
very large disagreement with others (Alibert et al. 1999). The large
differences between the models are likely caused by the very high sensitivity
of stellar evolution during core helium burning phase to even small changes in
the input physics, as discovered by Lauterborn, Refsdal and Weigert (1971).


title: The Star Formation History of LGS 3

abstract:
  We have determined the distance and star formation history of the Local Group
dwarf galaxy LGS 3 from deep Hubble Space Telescope WFPC2 observations. LGS 3
is intriguing because ground-based observations showed that, while its stellar
population is dominated by old, metal-poor stars, there is a handful of young,
blue stars. Also, the presence of HI gas makes this a possible ``transition
object'' between dwarf spheroidal and dwarf irregular galaxies. The HST data
are deep enough to detect the horizontal branch and young main sequence for the
first time. A new distance of D=620+/-20 kpc has been measured from the
positions of the TRGB, the red clump, and the horizontal branch. The mean
metallicity of the stars older than 8 Gyr is Fe/H = -1.5 +/- 0.3. The most
recent generation of stars has Fe/H ~ -1. For the first few Gyr the global star
formation rate was several times higher than the historical average and has
been fairly constant since then. However, we do see significant changes in
stellar populations and star formation history with radial position in the
galaxy. Most of the young stars are found in the central 63 pc (21''), where
the star formation rate has been relatively constant, while the outer parts
have had a declining star formation rate.


title: ATCA and CMB anisotropies

abstract:
  Australia Telescope Compact Array (ATCA) observations in sky regions selected
to be low in foreground confusion have been used to infer limits on
arcmin-scale CMB anisotropy in total intensity and polarization. These deep
searches have, hitherto, been made using the East-West ATCA in an ultra-compact
1-D array configuration and in the highest available frequency band at 3-cm
wavelength. The ATCA is being upgraded for operation at mm wavelengths and in
2-D array configurations: the enhanced capabilities present a new opportunity
for pursuing CMB anisotropy related observations with reduced foreground
confusion and at smaller angular scales.


title:
Reconstructing the equation of state for cold nuclear matter from the
  relationship of any two properties of neutron stars

abstract:
  A direct method is developed to reconstruct the equation of state for
high-density nuclear matter from the relationship between any two properties of
neutron stars, such as masses, radii, moments of inertia, baryonic masses,
binding energies, gravitational redshifts, and their combinations.


title: Are Galaxies Cosmon Lumps?

abstract:
  The scalar ``cosmon'' field mediating quintessence influences the dynamics of
extended objects in the universe. We discuss cosmon lumps -- spherically
symmetric solutions for the scalar field coupled to gravity. The two
integration constants can be associated to the mass and the rotational velocity
in a halo-like region with constant rotation curve. The presence of the scalar
field also changes the singularity of the black hole solution. We ask if
galaxies could be associated with cosmon lumps.


title:
An efficient parallel algorithm for O(N^2) direct summation method and
  its variations on distributed-memory parallel machines

abstract:
  We present a novel, highly efficient algorithm to parallelize O(N^2) direct
summation method for N-body problems with individual timesteps on
distributed-memory parallel machines such as Beowulf clusters. Previously known
algorithms, in which all processors have complete copies of the N-body system,
has the serious problem that the communication-computation ratio increases as
we increase the number of processors, since the communication cost is
independent of the number of processors. In the new algorithm, p processors are
organized as a $\sqrt{p}\times \sqrt{p}$ two-dimensional array. Each processor
has $N/\sqrt{p}$ particles, but the data are distributed in such a way that
complete system is presented if we look at any row or column consisting of
$\sqrt{p}$ processors. In this algorithm, the communication cost scales as $N
/\sqrt{p}$, while the calculation cost scales as $N^2/p$. Thus, we can use a
much larger number of processors without losing efficiency compared to what was
practical with previously known algorithms.


title:
Mid Infrared Spectral Energy Distribution of NGC 1068 with 0.1 arcsec
  Spatial Resolution

abstract:
  The central region of the Seyfert 2 galaxy NGC 1068 is imaged in the mid
infrared (MIR) using the Mid-Infrared Test Observation System on the 8.2 m
Subaru Telescope. The oversampling pixel scale associated with shift-and-add
method shows 0.1 arcsec resolution images with a high dynamic range after
deconvolution. Along with an extended structure at a position angle (P.A.) of
-10 degrees with higher surface brightness, another structure extends wider
with lower surface brightness at a P.A. of 20 degrees. The central peak
elongates north-south with FWHM of 0.3 x 0.2 arcsec. Spectral energy
distribution (SED) of the central peak is fitted to have the silicate
absorption feature of tau_9.7um = 0.9 +/- 0.3. This is half of the absorption
expected from the near-infrared (NIR) feature of carbonaceous dust. This
suggests a temperature gradient of the absorbing dust along the line of sight.
Another possibility, which is not distinguishable here, is the size
distribution of dust different from our Galaxy. Intrinsic luminosity of
emission from the central peak is 3 x 10^37 W. The SED shows a hint of the poly
aromatic hydrocarbon (PAH) emission features. Although a high spatial
resolution MIR spectrum is required, it suggests that the PAH carriers near the
active galactic nuclei (AGNs) are sheltered from the high-energy emission from
the AGNs and the AGNs have nuclear starbursts. For the NIR disklike structures,
no counterparts are detected in the MIR. The nature of the structures remains
unclear.


title: GRB 990704: the most X-ray rich BeppoSAX gamma-ray burst

abstract:
  We present the X- and $\gamma$-ray detection of GRB 990704 and the discovery
and study of its X-ray afterglow, 1SAX J1219.5-0350. Two pointed BeppoSAX
observations with the narrow field instruments were performed on this source,
separated in time by one week. The decay of the X-ray flux within the first
observation appears unusually slow, being best-fit by a power law with negative
index 0.83$\pm$0.16. Such a slow decay is consistent with the non-detection in
our second observation, but its back-extrapolation to the time of the GRB
largely underestimates the detected GRB X-ray prompt emission. In addition, the
GRB prompt event shows, among the BeppoSAX-WFC detected sample, unprecedentedly
high ratios of X- and gamma-ray peak fluxes (F$_{2-10 keV}$/F$_{40-700
keV}$$\sim$0.6, and F$_{2-26 keV}$/F$_{40-700 keV}$$\sim$1.6) and fluences
(S$_{2-10 keV}$/S$_{40-700 keV}$$\sim$1.5 and S$_{2-26 keV}$/S$_{40-700
keV}$$\sim$2.8), making it, among the BeppoSAX arcminute-localized GRBs, the
closest to the recently discovered class of Fast X-ray Transients.


title:
CCD drift-scan imaging lunar occultations: a feasible approach for
  sub-meter class telescopes

abstract:
  A CCD drift-scanning technique for lunar occultation (LO) observations is
presented. While this approach has been addressed before by Sturmann (1994) for
the case of large telescopes, the technical validity has never been discussed
for sub-meter class telescopes. In contrast to Sturmann's scheme, the proposed
technique places the CCD in the image plane of the telescope. This does not
represent a problem in the case of small telescopes, where the practical
angular resolution attainable by LO is not limited by aperture smoothing.
Photon-generated charge is read out at millisecond rate on a column-per-column
basis, as the diffraction pattern of the occulted star is being tracked. Two LO
events (SAO 79031 and SAO 77911) were observed to demonstrate the feasibility
of the method. Data analysis was carried out and no angular diameter the
observed stars were resolved. We show, however, that the technique could be
useful for close binary detections with small telescopes. A discussion of the
limiting resolution and magnitude imposed by our instrumentation is carried
out, showing that drift-scanning technique could be extended to 1-2m telescopes
for stellar diameter determination purposes. Finally, we point out that the
technical demands required by this technique can be easily met by most small
professional observatories and advanced amateurs.


title:
Colors and luminosities of the optical afterglows of the gamma-ray
  bursts

abstract:
  Results of the study of the color indices and luminosities of 17 optical
afterglows (OAs) of GRBs are presented. We show that the color variations
during the decline of OAs (except for GRB000131) are relatively small during
t-T_0 < 10 days and allow a comparison among them, even for the less densely
sampled OAs. The colors in the observer frame, corrected for the Galactic
reddening, concentrate at (V-R)_0 = 0.40 +- 0.13, (R-I)_0 = 0.46 +- 0.18,
(B-V)_0 = 0.47 +- 0.17. The color evolution of the OAs is negligible although
their brightness declines by several magnitudes during the considered time
interval. Such a strong concentration of the color indices also suggests that
the intrinsic reddening (inside their host galaxies) must be quite similar and
relatively small for all these events. The absolute brightness of OAs in the
observer frame, corrected for the host galaxy, lies within M_(R_0) = -26.5 to
-22.2 for (t-T_0)_rest = 0.25 days. This spread of M_(R_0) is not significantly
influenced by the shifts of lambda, caused by the different redshift z of the
respective OAs. The general decline rate of the OA sample considered here seems
to be independent of the absolute optical brightness of the OA, measured at
some t-T_0 identical for all OAs, and the light curves of all events are almost
parallel, when corrected for the redshift-induced time dilation.


title: On the black hole - bulge mass relation in active and inactive galaxies

abstract:
  New black-hole mass estimates are presented for a sample of 72 AGN covering
three decades in optical luminosity. Using a sub-sample of Seyfert galaxies,
which have black-hole mass estimates from both reverberation mapping and
stellar velocity dispersions, we investigate the geometry of the AGN broad-line
region (BLR). It is demonstrated that a model in which the orbits of the
line-emitting material have a flattened geometry is favoured over randomly
orientated orbits. Using this model we investigate the M_{bh}-L_{bulge}
relation for a combined 90-object sample, consisting of the AGN plus a sample
of 18 nearby inactive elliptical galaxies with dynamical black-hole mass
measurements. It is found that, for all reasonable mass-to-light ratios, the
M_{bh}-L_{bulge} relation is equivalent to a linear scaling between bulge and
black-hole mass. The best-fitting normalization of the M_{bh}-M_{bulge}
relation is found to be M_{bh}=0.0012M_{bulge}, in agreement with recent
black-hole mass studies based on stellar velocity dispersions. Furthermore, the
scatter around the M_{bh}-L_{bulge} relation for the full sample is found to be
significantly smaller than has been previously reported (Delta \log M_{bh}=0.39
dex). Finally, using the nearby inactive elliptical galaxy sample alone, it is
shown that the scatter in the M_{bh}-L_{bulge} relation is only 0.33 dex,
comparable to that of the M_{bh}-sigma relation. These results indicate that
reliable black-hole mass estimates can be obtained for high redshift galaxies.


title:
RR Lyrae Variables in the Globular Clusters of M31: a First Detection of
  Likely Candidates

abstract:
  The purpose of this paper is to show that RR Lyrae variables exist and can be
detected in M31 globular clusters. We report on the first tentative
identification of RR Lyrae candidates in four globular clusters of the
Andromeda galaxy, i.e. G11, G33, G64 and G322. Based on HST-WFPC2 archive
observations in the F555W and F814W filters spanning a total interval of about
5 consecutive hours we find evidence for 2, 4, 11 and 8 RR Lyrae variables of
both ab and c Bailey types in G11, G33, G64 and G322, respectively. Several
more candidates can be found by relaxing slightly the selection criteria. These
numbers are quite consistent with the horizontal branch morphology exhibited by
the four clusters, starting from the very blue HB in G11, and progressively
moving to redder HBs in G64, G33 and G322.


title: On the origin of highest energy gamma-rays from Mkn 501

abstract:
  The spectra of very high energy gamma-radiation from distant extragalactic
objects suffer significant deformations during the passage of primary
gamma-rays through the intergalactic medium. The recently reported fluxes of
diffuse infrared background radiation indicate that we detect, most probably,
heavily absorbed TeV radiation from Mkn 421 and Mkn 501. This implies that the
absorption-corrected spectrum of Mkn 501 may contain a sharp pile-up which
contradicts to the predictions of the conventional models of TeV blazars, and
thus may leads to the so-called "IR background-TeV gamma-ray crisis". To
overcome this difficulty, in this paper we propose two independent hypotheses
assuming that (i) the TeV radiation from Mkn 501 has a secondary origin, i.e.
it is formed during the development of electron-photon cascades in the
intergalactic medium initiated by primary gamma-rays; (ii) the pile-up in the
source spectrum is a result of comptonization (in deep Klein-Nishina regime) of
ambient optical radiation by an ultrarelativistic conical cold outflow (jet)
with bulk motion Lorentz factor Gamma_0 >= 3 10^7. Within the uncertainties
caused by the limited energy resolution of spectral measurements, the observed
TeV radiation of Mkn 501 formally can be explained by the intergalactic cascade
gamma-rays, assuming however an extremely low intergalactic magnetic field in
the direction to the source at the level of < 10^{-18} G. We also demonstrate
that the "bulk motion comptonization" scenario can quite naturally reproduce
the unusual spectral features in the absorption-corrected TeV spectrum of Mkn
501, and briefly discuss the astrophysical implications of this hypothesis.


title: A Remarkable Three Hour Thermonuclear Burst From 4U 1820-30

abstract:
  We present a detailed observational and theoretical study of a ~3 hr long
X-ray burst (the ``super burst'') observed by the Rossi X-ray Timing Explorer
(RXTE) from the low mass X-ray binary (LMXB) 4U 1820-30. This is the longest
X-ray burst ever observed from this source, and perhaps one of the longest ever
observed in great detail from any source. We show that the super burst is
thermonuclear in origin. The level of the accretion driven flux as well as the
total energy release of ~1.5 x 10^{42} ergs indicate that helium could not be
the energy source for the super burst. We outline the physics relevant to
carbon production and burning on helium accreting neutron stars and present
calculations of the thermal evolution and stability of a carbon layer and show
that this process is the most likely explanation for the super burst. We show
that for large columns of accreted carbon fuel, a substantial fraction of the
energy released in the carbon burning layer is radiated away as neutrinos, and
the heat that is conducted from the burning layer in large part flows inward,
only to be released on timescales longer than the observed burst. Thus the
energy released possibly exceeds that observed in X-rays by more than a factor
of ten. Spectral analysis during the super burst reveals the presence of a
broad emission line between 5.8 - 6.4 keV and an edge at 8 - 9 keV likely due
to reflection of the burst flux from the inner accretion disk in 4U 1820-30. We
believe this is the first time such a signature has been unambiguously detected
in the spectrum of an X-ray burst.


title: Enrichment of the Intergalactic Medium by the Milky Way Subgroup

abstract:
  I study the effect of the galaxies of the Milky Way subgroup on the chemical
enrichment of the diffuse gas within the Local Group. The preferred model
predicts that the present-day intergalactic medium mass is 1/22 of the initial
baryonic mass and its metallicity is 1/20 $Z_\odot$. Nearly 80 % of
intergalactic metals were produced in the Galactic bulge.


title: Open and closed CDM isocurvature models contrasted with the CMB data

abstract:
  We consider pure isocurvature cold dark matter models in the case of open and
closed universe. We allow for a large spectral tilt and scan the 6-dimensional
parameter space for the best fit to the COBE, Boomerang, and Maxima-1 data.
Taking into account constraints from large-scale structure and big bang
nucleosynthesis, we find a best fit with $\chi^2 = 121$, which is to be
compared to $\chi^2 = 44$ of a flat adiabatic reference model. Hence the
current data strongly disfavour pure isocurvature perturbations.


title:
On the use of Principal Component Analysis in analysing Cepheid light
  curves

abstract:
  We show how Principal Component Analysis can be used to analyse the structure
of Cepheid light curves. This method is more efficient than Fourier analysis at
bringing out changes in light curve shape as a function of period. Using this
technique, we study the shape of fundamental and first overtone mode Cepheid
light curves in the Galaxy, LMC and SMC over a wide period range. For
fundamentals, we find evidence for structural changes at $\log P \approx 1.55,
2.1$. It is suggested that the feature at $\log P \approx 2.1$ is associated
with a resonance in the Cepheid normal mode spectrum. For overtones, we recover
the Z shape in the $R_{21}$ period plane and reproduce the metallicity
dependence of this Z shape.


title:
Three Wide-Separation L dwarf Companions from the Two Micron All Sky
  Survey: Gl 337C, Gl 618.1B, and HD 89744B

abstract:
  We present two confirmed wide separation L-dwarf common proper motion
companions to nearby stars and one candidate identified from the Two Micron All
Sky Survey. Spectral types from optical spectroscopy are L0 V, L2.5 V, and L8
V. Near-infrared low resolution spectra of the companions are provided as well
as a grid of known objects spanning M6 V -- T dwarfs to support spectral type
assignment for these and future L-dwarfs in the z'JHK bands. Using published
measurements, we estimate ages of the companions from physical properties of
the primaries. These crude ages allow us to estimate companion masses using
theoretical low-mass star and brown dwarf evolutionary models. The new L-dwarfs
in this paper bring the number of known wide-binary (Separation >= 100 AU)
L-dwarf companions of nearby stars to nine. One of the L-dwarfs is a wide
separation companion to the F7 IV-V + extrasolar planet system HD89744Ab.


title: Applications of Tunable Imaging Filters for the VLT

abstract:
  Tunable imaging filters have been used for a variety of science programmes on
the Anglo-Australian and William Herschel Telescopes during the last five
years. This contribution describes these novel devices and reviews the science
(both Galactic and extragalactic) done with them. Possible strategies for
implementing a tunable filter at the VLT are also discussed. Significant
scientific potential exists for a tunable filter on the VLT, particularly in
the years before such capability becomes available on 8 -- 10 m-class
telescopes elsewhere.


title: Sherpa: a Mission-Independent Data Analysis Application

abstract:
  The ever-increasing quality and complexity of astronomical data underscores
the need for new and powerful data analysis applications. This need has led to
the development of Sherpa, a modeling and fitting program in the CIAO software
package that enables the analysis of multi-dimensional, multi-wavelength data.
In this paper, we present an overview of Sherpa's features, which include:
support for a wide variety of input and output data formats, including the new
Model Descriptor List (MDL) format; a model language which permits the
construction of arbitrarily complex model expressions, including ones
representing instrument characteristics; a wide variety of fit statistics and
methods of optimization, model comparison, and parameter estimation;
multi-dimensional visualization, provided by ChIPS; and new interactive
analysis capabilities provided by embedding the S-Lang interpreted scripting
language. We conclude by showing example Sherpa analysis sessions.


title: On the X-ray emission of Eta Carinae's outer ejecta

abstract:
  The extremely luminous and unstable star Eta Carinae is surrounded by ejecta
formed during the star's giant eruption around 1843. The optical nebula
consists of an inner region, the bipolar Homunculus and the outer ejecta. The
X-ray emission as detected in ROSAT and CHANDRA shows a hook shaped emission
structure mainly at the position of the outer ejecta substantially larger than
the Homunculus. We present results of a comparative study of the optical
morphology, the kinematics and the X-ray emission of the outer ejecta around
Eta Carinae. In general we find that the X-ray emission traces the shocks of
faster moving knots in the outer ejecta. First results of CHANDRA/ACIS data
will be presented, with spectra of selected areas in the outer ejecta giving
insight to the conditions (temperature, present elements and degree of
ionization) of the hot gas. The X-ray spectra will again be compared to the
kinematics of the gas as known from our optical spectra.


title: Large Bodies in the Kuiper Belt

abstract:
  We present a survey for bright Kuiper Belt Objects (KBOs) and Centaurs,
conducted at the Kitt Peak National Observatory (KPNO) 0.9 m telescope with the
KPNO 8k Mosaic CCD. The survey imaged 164 sq deg near opposition to a limiting
red magnitude of 21.1. Three bright KBOs and one Centaur were found, the
brightest KBO having red magnitude 19.7, about 700 km in diameter assuming a
dark Centaur-like 4% albedo. We estimate the power-law differential size
distribution of the Classical KBOs to have index q = 4.2 (+0.4)(-0.3), with the
total number of Classical KBOs with diameters larger than 100 km equal to 4.7
(+1.6)(-1.0) x 10^4. Additionally, we find that if there is a maximum object
size in the Kuiper Belt, it must be larger than 1000 km in diameter. By
extending our model to larger size bodies, we estimate that 30 (+16)(-12)
Charon-sized and 3.2 (+2.8)(-1.7) Pluto-sized Classical KBOs remain
undiscovered.


title: A Wavelet-Based Algorithm for the Spatial Analysis of Poisson Data

abstract:
  Wavelets are scaleable, oscillatory functions that deviate from zero only
within a limited spatial regime and have average value zero. In addition to
their use as source characterizers, wavelet functions are rapidly gaining
currency within the source detection field. Wavelet-based source detection
involves the correlation of scaled wavelet functions with binned,
two-dimensional image data. If the chosen wavelet function exhibits the
property of vanishing moments, significantly non-zero correlation coefficients
will be observed only where there are high-order variations in the data; e.g.,
they will be observed in the vicinity of sources.
  In this paper, we describe the mission-independent, wavelet-based source
detection algorithm WAVDETECT, part of the CIAO software package. Aspects of
our algorithm include: (1) the computation of local, exposure-corrected
normalized (i.e. flat-fielded) background maps; (2) the correction for exposure
variations within the field-of-view; (3) its applicability within the
low-counts regime, as it does not require a minimum number of background counts
per pixel for the accurate computation of source detection thresholds; (4) the
generation of a source list in a manner that does not depend upon a detailed
knowledge of the point spread function (PSF) shape; and (5) error analysis.
These features make our algorithm considerably more general than previous
methods developed for the analysis of X-ray image data, especially in the low
count regime. We demonstrate the algorithm's robustness by applying it to
various images.


title: The Effectiveness of the Canada-France-Hawaii Telescope

abstract:
  We have investigated the productivity and impact of the Canada-France-Hawaii
Telescope (CFHT) during its twenty-year history. CFHT has maintained a database
of refereed publications based on data obtained with CFHT since first light in
1979. For each paper, we analysed the cumulative number of citations and the
citation counts for each year, from data supplied by the NASA Astrophysics Data
System (ADS). We have compared citation counts retrieved from the ADS with
those from the Institute for Scientific Information (ISI) for a small sample of
papers. We have developed a procedure that allows us to compare citation counts
between older and newer papers in order to judge their relative impact. We
looked at the number of papers and citations not only by year, but also by the
instrument used to obtain the data. We also provide a preliminary look as to
whether programs given a higher ranking by the Time Allocation Committee (TAC)
produced papers with a higher number of citations.


title: Did the Universe Reionize at Redshift Six?

abstract:
  In light of recent observations of spectra of the quasars SDSS 1030+0524
(Becker et al. 2001) and SDSS 1044-0125 (Djorgovski et al. 2001), we study the
observational signatures of different stages of the reionization epoch. During
the initial, pre-overlap stage, the hydrogen throughout the universe is neutral
except for isolated HII bubbles due to individual ionizing sources. The central
stage of reionization is the overlap stage, during which the individual HII
bubbles overlap each other and reionize the low-density gas which takes up most
of the volume of the universe. Some neutral hydrogen remains in dense clumps
which are then slowly reionized during post-overlap. We show that both of the
recent observations are consistent with the post-overlap stage. Becker et al.
(2001) may have observed the universe in the era before the end of overlap, but
a conclusive proof of this requires the observation of similar intervals of
Gunn-Peterson absorption at the same redshift along several additional lines of
sight.


title: Novel Ways to Probe the Universe with Gamma-Ray Bursts and Quasars

abstract:
  I consider novel ways by which Gamma-Ray Bursts (GRBs) and quasars can be
used to probe the universe. Clues about how and when was the intergalactic
medium ionized can be read off the UV emission spectrum of GRB explosions from
the first generation of stars. The existence of intergalactic and galactic
stars can be inferred from their gravitational microlensing effect on GRB
afterglows. Prior to reionization, quasars should be surrounded by a halo of
scattered Lyman-alpha radiation which probes the neutral intergalactic medium
(IGM) around them. The situation is analogous to the appearance of a halo of
scattered light around a street lamp which is embedded in a dense fog. Outflows
from quasars magnetize the IGM at all redshifts. As a result, the shocks
produced by converging flows during the formation of large scale structure in
the IGM, accelerate electrons to relativistic energies and become visible in
the radio regime through their synchrotron emission and in the gamma-ray regime
through their inverse-Compton scattering of the microwave background photons.
During transient episodes of strong mergers, X-ray clusters should therefore
appear as extended radio or gamma-ray sources on the sky.


title:
Galaxy number counts in the Hubble Deep Field as a strong constraint on
  a hierarchical galaxy formation model

abstract:
  Number counts of galaxies are re-analyzed using a semi-analytic model (SAM)
of galaxy formation based on the hierarchical clustering scenario. We have
determined the astrophysical parameters in the SAM that reproduce observations
of nearby galaxies, and used them to predict the number counts and redshifts of
faint galaxies for three cosmological models for (1) the standard cold dark
matter (CDM) universe, (2) a low-density flat universe with nonzero
cosmological constant, and (3) a low-density open universe with zero
cosmological constant. The novelty of our SAM analysis is the inclusion of
selection effects arising from the cosmological dimming of surface brightness
of high-redshift galaxies, and also from the absorption of visible light by
internal dust and intergalactic \ion{H}{1} clouds. Contrary to previous SAM
analyses which do not take into account such selection effects, we find, from
comparison with observed counts and redshifts of faint galaxies in the Hubble
Deep Field (HDF), that the standard CDM universe is {\it not} preferred, and a
low-density universe either with or without cosmological constant is favorable,
as suggested by other recent studies. Moreover, we find that a simple
prescription for the time scale of star formation (SF), being proportional to
the dynamical time scale of the formation of the galactic disk, is unable to
reproduce the observed number- redshift relation for HDF galaxies, and that the
SF time scale should be nearly independent of redshift, as suggested by other
SAM analyses for the formation of quasars and the evolution of damped
Ly-$\alpha$ systems.


title:
Environmental Effects on Evolution of Cluster Galaxies in a LCDM
  Universe

abstract:
  We investigate environmental effects on evolution of bright cluster galaxies
in a $\Lambda$ dominated cold dark matter universe using a combination of
dissipationless N-body simulations and a semi-analytic galaxy formation model.
The N-body simulations enable us to calculate orbits of galaxies in simulated
clusters. Therefore we can incorporate stripping of cold gas from galactic
disks by ram pressure from intracluster medium into our model. In this paper we
study how ram pressure stripping (RPS) and small starburst induced by a minor
merger affect colors, star formation rates, and morphologies of cluster
galaxies. We find that the RPS is not important for colors and SFRs of galaxies
in the cluster core if star formation time-scale is properly chosen, because
the star formation is sufficiently suppressed by consumption of the cold gas in
the disks. Then observed color and SFR gradients can be reproduced without the
RPS. The small starburst triggered by a minor merger hardly affects the SFRs
and colors of the galaxies as well. We also examine whether these two processes
can resolve the known problem that the major merger-driven bulge formation
scenario predict too few galaxies of intermediate bulge-to-total luminosity
ratio (B/T) in clusters. When the minor burst is taken into account, the
intermediate B/T population is increased and the observed morphology gradients
in clusters are successfully reproduced. When the minor burst is considered,
the RPS also plays an important role in formation of the intermediate B/T
galaxies. We present redshift evolution of morphological fractions predicted by
our models. The predicted number ratios of the intermediate B/T galaxies to the
bulge-dominated galaxies show nearly flat or slightly increasing trends with
increasing redshift.


title: Infrared Photometry of Late-M, L, and T Dwarfs

abstract:
  We present ZJHKL'M' photometry of a sample of 58 late-M, L, and T dwarfs,
most of which are identified from the Sloan Digital Sky Survey and the Two
Micron All-Sky Survey. Near-infrared spectra and spectral classifications for
most of this sample are presented in a companion paper by Geballe et al. We
derive the luminosities of 18 dwarfs in the sample and the results imply that
the effective temperature range for the L dwarfs in our sample is approximately
2200-1300 K and for the T dwarfs 1300-800 K. We obtained new photometric data
at the United Kingdom Infrared Telescope for: 42 dwarfs at Z, 34 dwarfs at JHK,
21 dwarfs at L', as well as M' data for two L dwarfs and two T dwarfs. The M'
data provide the first accurate photometry for L and T dwarfs in this bandpass
- for a T2 and a T5 dwarf, we find K-M'=1.2 and 1.6, respectively. These colors
are much bluer than predicted by models suggesting that CO may be more abundant
in these objects than expected, as has been found for the T6 dwarf Gl 229B. We
also find that K-L' increases monotonically through most of the M, L, and T
subclasses, but it is almost constant between types L6 and T5. The degeneracy
is probably due to the onset of methane absorption at the blue edge of the L'
bandpass. The JHK colors of L dwarfs show significant scatter, suggesting that
the fluxes in these bandpasses are sensitive to variations in photospheric dust
properties. The H-K colors of the later T dwarfs also show some scatter which
we suggest is due to variations in pressure-induced molecular hydrogen opacity,
which is sensitive to gravity and metallicity.


title: GRB 010222: A Burst Within a Starburst

abstract:
  We present millimeter and submillimeter wavelength observations and
near-infrared K-band imaging toward the bright gamma-ray burst GRB 010222. Over
seven epochs the flux density of the source was constant with an average flux
density 3.74+/-0.53 mJy at 350 GHz and 1.05+/-0.22 mJy at 250 GHz, giving a
spectral index alpha=3.78+/-0.25. We rule out the possibility that this
emission originated from the burst or its afterglow and we conclude that it is
due to a dusty, high redshift starburst galaxy (SMM J14522+4301). We argue that
the host galaxy of GRB 010222 is the most plausible counterpart of SMM
J14522+4301, based in part on the centimeter detection of the host at the
expected level. The optical/NIR properties of the host galaxy of GRB 010222
suggest that it is a blue, sub-L_*, similar to other GRB host galaxies. This
contrasts with the enormous far-infrared luminosity of this galaxy based on our
submillimeter detection (L_Bol~4X10^{12} L_odot). We suggest that this GRB host
galaxy has a very high star formation rate, SFR 600 M_\odot/yr, most of which
is unseen at optical wavelengths.


title:
The Self-Enrichment of Galactic Halo Globular Clusters: the
  mass-metallicity relation

abstract:
  We discuss the existence of a mass-metallicity relation among galactic halo
globular clusters. The lack of any luminosity-metallicity correlation in
globular cluster systems has been used as an argument against self-enrichment
models of cluster formation. We show that such a relation is statistically
present among the galactic Old Halo globulars. This observational correlation
implies that the least massive old clusters are the most metal-rich. This is in
contradiction with the idea that, if globular clusters were self-enriched
systems, the most metal-rich clusters would also be the most massive ones. We
further show that this anti-correlation is as predicted by self-enrichment
models.


title: X-Ray spectra from protons illuminating a neutron star

abstract:
  We consider the interaction of a slowly rotating unmagnetized neutron star
with a hot (ion supported, ADAF) accretion flow. The virialized protons of the
ADAF penetrate into the neutron star atmosphere, heating a surface layer.
Detailed calculations are presented of the equilibrium between heating by the
protons, electron thermal conduction, bremsstrahlung and multiple Compton
scattering in this layer. Its temperature is of the order 40-70 keV. Its
optical depth increases with the incident proton energy flux, and is of the
order unity for accretion at $10^{-2}$--$10^{-1}$ of the Eddington rate. At
these rates, the X-ray spectrum produced by the layer has a hard tail extending
to 100 keV, and is similar to the observed spectra of accreting neutron stars
in their hard states. The steep gradient at the base of the heated layer gives
rise to an excess of photons at the soft end of the spectrum (compared to a
blackbody) through an `inverse photosphere effect'. The differences with
respect to previous studies of similar problems are discussed, they are due
mostly to a more accurate treatment of the proton penetration process and the
vertical structure of the heated layer.


title:
Angular and three--dimensional correlation functions, determined from
  the Muenster Red Sky Survey

abstract:
  We measured the two dimensional galaxy--galaxy correlation function from the
Muenster Red Sky Survey (Ungruhe 1999). This survey has a slightly larger
surface as the APM survey and complete up to r_F<18.3 mag (z_{med} \sim 0.14).
The large dynamical range of the survey made it possible to examine
sub-catalogues with different limiting magnitudes. The positive part of our
measured angular correlation functions (after the colour correction) agree
excellently with those measured by Maddox, Efstathiou and Shutherland 1996 from
the APM galaxy catalogue (Maddox et al. 1990). From the measured angular
correlation functions the three dimensional two-point correlation function
\xi(r) was calculated. We have chosen the evolution parameter \epsilon so that
the change of the correlation length r_0 with the depth of the sub-catalogue
were minimal. This prescription gives r_0 = 5.82 \pm 0.05 h^{-1} Mpc and a
high, positive evolution parameter \epsilon = 2.6. We have estimated the
average inflow/outflow velocity, corresponding to the evolution of the 3d
correlation function. The position of the point, where the 3d correlation
function breaks away from the power law depends on the depth of the
sub-catalogues: for low magnitude limits the break-down comes earlier, for
higher later.


title:
Distant FR I radio galaxies in the Hubble Deep Field: implications for
  the cosmological evolution of radio-loud AGN

abstract:
  Deep and high resolution radio observations of the Hubble Deep Field and
flanking fields have shown the presence of two distant edge-darkened FR I radio
galaxies, allowing for the first time an estimate of their high redshift space
density. If it is assumed that the space density of FR I radio galaxies at z>1
is similar to that found in the local universe, then the chance of finding two
FR I radio galaxies at these high radio powers in such a small area of sky is
<1%. This suggests that these objects were significantly more abundant at z>1
than at present, effectively ruling out the possibility that FR I radio sources
undergo no cosmological evolution. We suggest that FR I and FR II radio
galaxies should not be treated as intrinsically distinct classes of objects,
but that the cosmological evolution is simply a function of radio power with FR
I and FR II radio galaxies of similar radio powers undergoing similar
cosmological evolutions. Since low power radio galaxies have mainly FR I
morphologies and high power radio galaxies have mainly FR II morphologies, this
results in a generally stronger cosmological evolution for the FR IIs than the
FR Is. We believe that additional support from the V/Vmax test for evolving and
non-evolving populations of FR IIs and FR Is respectively is irrelevant, since
this test is sensitive over very different redshift ranges for the two classes.


title:
A New Distance Estimator and Spatial Distribution of GRBS Observed by
  BATSE

abstract:
  We propose a redshift estimator for the long ($T_{90} > 20$) gamma-ray bursts
(GRBs) observed by the BATSE. It is based on an empirical relation between the
redshift and the power-law index of power density spectra (PDSs) of the
observed GRBs. This relation is constructed by using the fact that the
power-law index is dependent upon a characteristic timescale of GRB light
curves which are inevitably stretched by cosmological time dilation. We
construct the empirical relation using both individual PDSs and averaged PDSs.
An error estimates of $z$ are 1.09 and 1.11 for the empirical relation by
individual PDS fits, 1.72 and 1.56 by averaged PDS fits, for the least squares
fit and the maximum likelihood fit, respectively. We attempt to determine the
spatial distribution of the GRBs observed by the BATSE as a function of
redshifts on the basis of the resulting redshift estimator. We find that the
obtained spatial distribution of the observed GRBs seems consistent with that
of the GRBs whose redshifts are reported, even though the estimated errors are
not very accurate. The GRBs observed by the BATSE seem distributed within $z
\sim 5-6$. This result has implications on theoretical calculations of stellar
formations at high redshifts and beaming geometry via a statistical study of
the observed GRBs involving beaming-induced luminosity functions. We discuss
such implications, and possible uncertainties of the suggested method.


title: AGAPE : Gravitational microlensing effect to look for MACHOs towards M31

abstract:
  We report the discovery of a short-duration microlensing candidate in the
Northern field of the POINT-AGAPE pixel lensing survey towards M31. The
full-width at half-maximum timescale is very short (tfwhm = 1.8 days) and the
source star has almost certainly been identified on HST images, allowing to
infer an Einstein crossing time : te=10.4 days and a magnification at maximum :
Amax=18.


title:
Towards Spectral Classification of L and T Dwarfs: Infrared and Optical
  Spectroscopy and Analysis

abstract:
  We present 0.6-2.5um, R~400 spectra of twenty-seven cool, low luminosity
stars and substellar objects. Based on these and previously published spectra
we develop a preliminary spectral classification system for L and T dwarfs. For
late L and T types the classification system is based entirely on four spectral
indices in the 1-2.5um interval. Two of these indices are derived from water
absorption bands at 1.15um and 1.4um, the latter of which shows a smooth
increase in depth through the L and T sequences and can be used to classify
both spectral types. The other two indices make use of methane absorption
features in the H and K bands, with the K band index also applicable to mid to
late L dwarfs. Continuum indices shortward of 1um used by previous authors to
classify L dwarfs are found to be useful only through mid L subclasses. We
employ the 1.5um water index and the 2.2um methane index to complete the L
classification through L9.5 and to link the new system with a modified version
of the 2MASS ``Color-d'' index. By correlating the depths of the methane and
water absorption features, we establish a T spectral sequence from types T0 to
T8, based on all four indices, which is a smooth continuation of the L
sequence. We reclassify two 2MASS L8 dwarfs as L9 and L9.5 and identify one
SDSS object as L9. In the proposed system methane absorption appears in the K
band approximately at L8, two subclasses earlier than its appearance in the H
band. The L and T spectral classes are distinguished by the absence and
presence, respectively, of H band methane absorption.


title: Web Availability of MACHO Data

abstract:
  The MACHO Project generated two-color photometric lightcurves for 73 million
stars in the LMC, SMC, and the galactic bulge during its 8 years of observing.
This photometry, along with all images and a catalog of LMC variable stars, is
now available for viewing or download from the MACHO Project websites,
http://wwwmacho.anu.edu.au/ or http://wwwmacho.mcmaster.ca/ . The capabilities
and organization of the new data retrieval facility is described in this paper.


title: The deepest X-ray look at the Universe

abstract:
  The origin of the X-ray background, in particular at hard (2-10 keV)
energies, has been a debated issue for more than 30 years. The Chandra deep
fields provide the deepest look at the X-ray sky and are the best dataset to
study the X-ray background. We searched the Chandra Deep Field South for X-ray
sources with the aid of a dedicated wavelet-based algorithm. We are able to
reconstruct the Log N-Log S source distribution in the soft (0.5-2 keV) and
hard (2-10 keV) bands down to limiting fluxes of 2x10^{-17} erg s^{-1} cm^{-2}
and 2x10^{-16} erg s^{-1} cm^{-2}, respectively. These are a factor ~5 deeper
than previous investigations. We find that the soft relation continues along
the extrapolation from higher fluxes, almost completely accounting for the soft
X-ray background. On the contrary, the hard distribution shows a flattening
below ~2x10^{-14} erg s^{-1} cm^{-2}. Nevertheless, we can account for >68% of
the hard X-ray background, with the main uncertainty being the sky flux itself.


title: Radiation from collision-dominated relativistic pair fireballs

abstract:
  It is generally accepted that gamma-ray bursts (GRBs) are initiated by a
relativistic pair fireball, converting its internal energy into kinetic energy
of a relativistically moving plasmoid and subsequently into radiation. Here, we
investigate the early stages of this evolution, after the pair fireball has
become optically thin to gamma-gamma pair production. We show that for a short
period of time, ~ 0.1 - a few seconds after the initial explosion, the pair
plasmoid evolution might be dominated by collisional processes prior to the
formation of a collisionless shock. We simulate these processes during the
early pair plasmoid evolution and calculate the expected radiative signatures.
We show that the radiation from the collision-dominated pair plasmoid phase
results in a short (~ a few ms) flash of thermal soft X-ray emission, followed
by a transition phase of < 1 s during which the fireball turns Thomson thin,
but its radiation remains dominated by thermal Comptonization, peaking at
around E_pk ~ 100 MeV - a few GeV. While the very early thermal emission could
be associated with the quasi-thermal radiation signatures found in the very
early phases of several bright BATSE GRBs, the predicted subsequent flash of
high-energy emission should be easily detectable with the GLAST satellite.


title: Neutrinos from Early-Phase, Pulsar-Driven Supernovae

abstract:
  Neutron stars, just after their formation, are surrounded by expanding,
dense, and very hot envelopes which radiate thermal photons. Iron nuclei can be
accelerated in the wind zones of such energetic pulsars to very high energies.
These nuclei photo-disintegrate and their products lose energy efficiently in
collisions with thermal photons and with the matter of the envelope, mainly via
pion production. When the temperature of the radiation inside the envelope of
the supernova drops below $\sim 3\times 10^6$ K, these pions decay before
losing energy and produce high energy neutrinos. We estimate the flux of muon
neutrinos emitted during such an early phase of the pulsar - supernova envelope
interaction. We find that a 1 km$^2$ neutrino detector should be able to detect
neutrinos above 1 TeV within about one year after the explosion from a
supernova in our Galaxy. This result holds if these pulsars are able to
efficiently accelerate nuclei to energies $\sim 10^{20}$ eV, as postulated
recently by some authors for models of Galactic acceleration of the extremely
high energy cosmic rays (EHE CRs).


title:
Identification of a strong emission line at 2.8935 mu in the spectrum of
  the Orion Nebula

abstract:
  A strong emission line at 2.8935 mu discovered by Rubin et al. (2001) in an
ISO SWS02 spectrum of the Orion Nebula is identified as the 4p - 4s multiplet
of the O I triplets. Line formation is due to de-excitation cascades following
UV-pumping of high triplet terms and occurs in the O I zone immediately behind
the Hydrogen ionization front. This cascade mechanism also accounts for
permitted O I triplet lines in the optical spectrum (Grandi 1975). An escape
probability treatment of the O I cascades accounts for the strength of the 2.89
mu line and suggests interesting diagnostic possibilities for the optical
lines.


title: The chemical enrichment of the ICM with BeppoSAX

abstract:
  We review observations on the chemical enrichment of the intracluster medium
(ICM) performed using BeppoSAX MECS data. The picture emerging is that
non-cooling flow clusters have flat metallicity profiles, whereas a strong
enhancement in the abundance is found in the central regions of the cooling
flow clusters. All the non-cooling flow clusters present evidence of recent
merger activity suggesting that the merger events redistributes efficiently the
metal content of the ICM. The observed abundance excess in the central regions
of cooling flow clusters is probably due to metals ejected from the cD galaxy
located in the cluster core. Cooling flow cluster have also enhanced Nickel
abundances in their cores with respect to the non cooling flow clusters.


title:
R-Modes on Rapidly Rotating, Relativistic Stars: I. Do Type-I Bursts
  Excite Modes in the Neutron-Star Ocean?

abstract:
  During a Type-I burst, the turbulent deflagation front may excite waves in
the neutron star ocean and upper atmosphere with frequencies, $\omega \sim 1$
Hz. These waves may be observed as highly coherent flux oscillations during the
burst. The frequencies of these waves changes as the upper layers of the
neutron star cool which accounts for the small variation in the observed QPO
frequencies. In principle several modes could be excited but the fundamental
buoyant $r-$mode exhibits significantly larger variability for a given
excitation than all of the other modes. An analysis of modes in the burning
layers themselves and the underlying ocean shows that it is unlikely these
modes can account for the observed burst oscillations. On the other hand,
photospheric modes which reside in a cooler portion of the neutron star
atmosphere may provide an excellent explanation for the observed oscillations.


title:
Non-LTE, Relativistic Accretion Disk Fits to 3C~273 and the Origin of
  the Lyman Limit Spectral Break

abstract:
  We fit general relativistic, geometrically thin accretion disk models with
non-LTE atmospheres to near simultaneous multiwavelength data of 3C~273,
extending from the optical to the far ultraviolet. Our model fits show no flux
discontinuity associated with a hydrogen Lyman edge, but they do exhibit a
spectral break which qualitatively resembles that seen in the data. This break
arises from relativistic smearing of Lyman emission edges which are produced
locally at tens of gravitational radii in the disk. We discuss the possible
effects of metal line blanketing on the model spectra, as well as the
substantial Comptonization required to explain the observed soft X-ray excess.
Our best fit accretion disk model underpredicts the near ultraviolet emission
in this source, and also has an optical spectrum which is too red. We discuss
some of the remaining physical uncertainties, and suggest in particular that an
extension of our models to the slim disk regime and/or including nonzero
magnetic torques across the innermost stable circular orbit may help resolve
these discrepancies.


title:
The Spectra of T Dwarfs I: Near-Infrared Data and Spectral
  Classification

abstract:
  We present near-infrared spectra for a sample of T dwarfs, including eleven
new discoveries made using the Two Micron All Sky Survey. These objects are
distinguished from warmer (L-type) brown dwarfs by the presence of methane
absorption bands in the 1--2.5 $\micron$ spectral region. A first attempt at a
near-infrared classification scheme for T dwarfs is made, based on the
strengths of CH$_4$ and H$_2$O bands and the shapes of the 1.25, 1.6, and 2.1
$\micron$ flux peaks. Subtypes T1 V through T8 V are defined, and spectral
indices useful for classification are presented. The subclasses appear to
follow a decreasing T$_{eff}$ scale, based on the evolution of CH$_4$ and
H$_2$O bands and the properties of L and T dwarfs with known distances.
However, we speculate that this scale is not linear with spectral type for cool
dwarfs, due to the settling of dust layers below the photosphere and subsequent
rapid evolution of spectral morphology around T$_{eff}$ $\sim$ 1300--1500 K.
Similarities in near-infrared colors and continuity of spectral features
suggest that the gap between the latest L dwarfs and earliest T dwarfs has been
nearly bridged. This argument is strengthened by the possible role of CH$_4$ as
a minor absorber shaping the K-band spectra of the latest L dwarfs. Finally, we
discuss one peculiar T dwarf, 2MASS 0937+2931, which has very blue
near-infrared colors (J-K$_s$ = $-0.89\pm$0.24) due to suppression of the 2.1
$\micron$ peak. The feature is likely caused by enhanced collision-induced
H$_2$ absorption in a high pressure or low metallicity photosphere.


title:
Analysis of a Proper-Motion Selected Sample of Stars in the Ursa Minor
  Dwarf Spheroidal Galaxy

abstract:
  We have studied the stellar population and internal structure of the core of
the Ursa Minor dwarf spheroidal galaxy, using a sample of stars selected to be
members based on their proper motions. In agreement with previous studies, we
find Ursa Minor to be dominated by an old, metal-poor stellar population. A
small number of stars with high membership probabilities lie redward of the red
giant branch. The brightest (V <= 18) such stars are known to be Carbon stars,
rather than metal-rich first-ascent giants. A number of stars with high
membership probabilities lie blueward of the red giant branch, and are more
luminous than the horizontal branch. We speculate that these are
post-horizontal branch stars. There may also be one or two stars in the
post-AGB phase. Spectroscopy of the candidate post-HB and post-AGB stars is
required to determine their nature. We recover the internal substructure in
Ursa Minor that has been noted by several authors in the last 15 years. Using a
variety of two- and three-dimensional statistical tests, we conclude that this
substructure is statistically significant at the 0.005 level. There is no
evidence that the regions of density excess have stellar populations that
differ from the main body of Ursa Minor. The crossing time for a typical
density excess is only ~5 million years. They are therefore clearly not due to
intermediate age star-forming bursts. We conclude that they are instead due to
tidal interactions between the Galaxy and Ursa Minor.


title: Protostellar Evolution during Time Dependent, Anisotropic Collapse

abstract:
  The formation and collapse of a protostar involves the simultaneous infall
and outflow of material in the presence of magnetic fields, self-gravity, and
rotation. We use self-similar techniques to self-consistently model the
anisotropic collapse and outflow by a set of angle-separated self-similar
equations. The outflow is quite strong in our model, with the velocity
increasing in proportion to radius, and material formally escaping to infinity
in the finite time required for the central singularity to develop.
  Analytically tractable collapse models have been limited mainly to
spherically symmetric collapse, with neither magnetic field nor rotation. Other
analyses usually employ extensive numerical simulations, or either perturbative
or quasistatic techniques. Our model is unique as an exact solution to the
non-stationary equations of self-gravitating MHD, which features co-existing
regions of infall and outflow.
  The velocity and magnetic topology of our model is quadrupolar, although
dipolar solutions may also exist. We provide a qualitative model for the origin
and subsequent evolution of such a state. However, a central singularity forms
at late times, and we expect the late time behaviour to be dominated by the
singularity rather than to depend on the details of its initial state. Our
solution may, therefore, have the character of an attractor among a much more
general class of self-similarity.


title: Pachmarhi Array of \v{C}erenkov Telescopes and its Sensitivity

abstract:
  Pachmarhi Array of \v{C}erenkov Telescopes (PACT) has been designed to search
for celestial TeV $\gamma-$rays using the wavefront sampling technique. PACT,
located at Pachmarhi, (latitude 22$^\circ$ 28$^\prime$ N, longitude 76$^\circ$
26$^\prime$ E, altitude 1075 m) consists of 25 telescopes deployed over an area
of 80 m $\times$ 100m. Each telescopes consists of 7 parabolic reflectors, each
viewed by a fast phototube behind a 3$^\circ$ mask at the focus. The density
and the arrival time of the photons at the PMT are recorded for each shower.
The energy threshold and collection area of the array are estimated, from Monte
Carlo simulations, to be $\sim$ 900 GeV and 10$^5$ m$^2$ respectively. The
accuracy in determination of arrival angle of a shower is estimated to be about
0.1$^\circ$ in the near vertical direction. About 99% of the off-axis hadronic
events could be rejected from directional information alone. Further, at least
75% of the on-axis hadronic events could be rejected using species sensitive
parameters derived from timing and density measurements. These cuts on data to
reject background would retain $\sim$ 44% of the $\gamma-$ray signal. The
sensitivity of the array for a 5$\sigma$ detection of $\gamma-$ray signal at a
threshold energy of 1 TeV has been estimated to be $\sim$ 4.1 $\times$
10$^{-12}$ photons cm$^{-2}$ s$^{-1}$ for an on source exposure of 50 hours.
The PACT set-up has been fully commissioned and is collecting data. The details
of the system parameters and sensitivity will be presented.


title: 1RXS J214303.7+065419/RBS 1774: A New Isolated Neutron Star Candidate

abstract:
  We report on the identification of a new possible Isolated Neutron Star
candidate in archival ROSAT observations. The source 1RXS J214303.7+065419,
listed in the ROSAT Bright Survey as RBS 1774, is very soft, exhibits a thermal
spectrum well fitted by a blackbody at ${T}\sim 90$ eV and has a low column
density, ${N_H}\sim 5\times 10^{20}$ ${cm}^{-2}$. Catalogue searches revealed
no known sources in other energy bands close to the X-ray position of RBS 1774.
Follow-up optical observations with NTT showed no peculiar object within the
X-ray error circle. The absence of any plausible optical counterpart down to
${m_R}\sim 23$ results in an X-ray to optical flux ratio in excess of 1000.