7,058 research outputs found
Gravitationally Lensed Gamma-Ray Bursts as Probes of Dark Compact Objects
If dark matter in the form of compact objects comprises a large fraction of
the mass of the universe, then gravitational lensing effects on gamma-ray
bursts are expected. We utilize BATSE and Ulysses data to search for lenses of
different mass ranges, which cause lensing in the milli, pico, and femto
regimes. Null results are used to set weak limits on the cosmological abundance
of compact objects in mass ranges from 10 to 10 . A
stronger limit is found for a much discussed universe dominated
by black holes of masses , which is ruled out at the
90% confidence level.Comment: 14 pages, 4 figures, fixed minor corrections. Accepted for
publication in ApJ(L
The Interplanetary Network Supplement to the BeppoSAX Gamma-Ray Burst Catalogs
Between 1996 July and 2002 April, one or more spacecraft of the
interplanetary network detected 787 cosmic gamma-ray bursts that were also
detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera
experiments aboard the BeppoSAX spacecraft. During this period, the network
consisted of up to six spacecraft, and using triangulation, the localizations
of 475 bursts were obtained. We present the localization data for these events.Comment: 89 pages, 3 figures. Submitted to the Astrophysical Journal
Supplement Serie
Direct N-body Modelling of Stellar Populations: Blue Stragglers in M67
We present a state-of-the-art N-body code which includes a detailed treatment
of stellar and binary evolution as well as the cluster dynamics. This code is
ideal for investigating all aspects relating to the evolution of star clusters
and their stellar populations. It is applicable to open and globular clusters
of any age. We use the N-body code to model the blue straggler population of
the old open cluster M67. Preliminary calculations with our binary population
synthesis code show that binary evolution alone cannot explain the observed
numbers or properties of the blue stragglers. On the other hand, our N-body
model of M67 generates the required number of blue stragglers and provides
formation paths for all the various types found in M67. This demonstrates the
effectiveness of the cluster environment in modifying the nature of the stars
it contains and highlights the importance of combining dynamics with stellar
evolution. We also perform a series of N = 10000 simulations in order to
quantify the rate of escape of stars from a cluster subject to the Galactic
tidal field.Comment: 26 pages, 18 figures, accepted for publication in MNRA
A Complete N-body Model of the Old Open Cluster M67
The old open cluster M67 is an ideal testbed for current cluster evolution
models because of its dynamically evolved structure and rich stellar
populations that show clear signs of interaction between stellar, binary and
cluster evolution. Here we present the first truly direct N-body model for M67,
evolved from zero age to 4 Gyr taking full account of cluster dynamics as well
as stellar and binary evolution. Our preferred model starts with 12000 single
stars and 12000 binaries placed in a Galactic tidal field at 8.0 kpc from the
Galactic Centre. Our choices for the initial conditions and for the primordial
binary population are explained in detail. At 4 Gyr, the age of M67, the total
mass has reduced by 90% as a result of mass loss and stellar escapes. The mass
and half-mass radius of luminous stars in the cluster are a good match to
observations although the model is more centrally concentrated than
observations indicate. The stellar mass and luminosity functions are
significantly flattened by preferential escape of low-mass stars. We find that
M67 is dynamically old enough that information about the initial mass function
is lost, both from the current luminosity function and from the current mass
fraction in white dwarfs. The model contains 20 blue stragglers at 4 Gyr which
is slightly less than the 28 observed in M67. Nine are in binaries. The blue
stragglers were formed by a variety of means and we find formation paths for
the whole variety observed in M67. Both the primordial binary population and
the dynamical cluster environment play an essential role in shaping the
population. A substantial population of short-period primordial binaries (with
periods less than a few days) is needed to explain the observed number of blue
stragglers in M67.Comment: 32 pages, 17 figures, submitted to MNRA
BATSE Observations of Gamma-Ray Burst Tails
I discuss in this paper the phenomenon of post-burst emission in BATSE
gamma-ray bursts at energies traditionally associated with prompt emission. By
summing the background-subtracted signals from hundreds of bursts, I find that
tails out to hundreds of seconds after the trigger may be a common feature of
long events (duration greater than 2s), and perhaps of the shorter bursts at a
lower and shorter-lived level. The tail component appears independent of both
the duration (within the long GRB sample) and brightness of the prompt burst
emission, and may be softer. Some individual bursts have visible tails at
gamma-ray energies and the spectrum in at least a few cases is different from
that of the prompt emission.Comment: 33 Pages from LaTex including 7 figures, with aastex. To appear in
Astrophysical Journa
Stereoscopic observations of hard x ray sources in solar flares made with GRO and other spacecraft
Since the launch of the Gamma Ray Observatory (GRO) in Apr. 1991, the Burst and Transient Source Experiment (BATSE) instrument on GRO has recorded a large number of solar flares. Some of these flares have also been observed by the Gamma-Ray Burst Detector on the Pioneer Venus Orbiter (PVO) and/or by the Solar X-Ray/Cosmic Gamma-Ray Burst Experiment on the Ulysses spacecraft. A preliminary list of common flares observed during the period May-Jun. 1991 is presented and the possible joint studies are indicated
No Evidence for Gamma-Ray Burst/Abell Cluster or Gamma- Ray Burst/Radio-Quiet Quasar Correlations
We examine the recent claims that cosmic gamma-ray bursts are associated with
either radio-quiet quasars or Abell clusters. These associations were based on
positional coincidences between cataloged quasars or Abell clusters, and
selected events from the BATSE 3B catalog of gamma-ray bursts. We use a larger
sample of gamma-ray bursts with more accurate positions, obtained by the 3rd
Interplanetary Network, to re-evaluate these possible associations. We find no
evidence for either.Comment: Accepted for publication in the Astrophysical Journa
Cooling of 2 kW H subscript 2-O subscript 2 fuel cell
An extensive research and development program has been carried out to devise an improved method of removing waste heat of reaction from a developmental 2 kW hydrogen-oxygen fuel cell
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