69 research outputs found

### Likelihood Analysis of Repeating in the BATSE Catalogue

I describe a new likelihood technique, based on counts-in-cells statistics,
that I use to analyze repeating in the BATSE 1B and 2B catalogues. Using the 1B
data, I find that repeating is preferred over non-repeating by 4.3:1 odds, with
a well-defined peak at 5-6 repetitions per source. I find that the post-1B data
are consistent with the repeating model inferred from the 1B data, after taking
into account the lower fraction of bursts with well-determined positions.
Combining the two data sets, I find that the odds favoring repeating over
non-repeating are almost unaffected at 4:1, with a narrower peak at 5
repetitions per source. I conclude that the data sets are consistent both with
each other and with repeating, and that for these data sets the odds favor
repeating.Comment: 5 pages including 3 encapsulated figures, as a uuencoded, gzipped,
Postscript file. To appear in Proc. of the 1995 La Jolla workshop ``High
Velocity Neutron Stars and Gamma-Ray Bursts'' eds. Rothschild, R. et al.,
AIP, New Yor

### A model independent lower limit on the number of Gamma Ray Burst hosts from repeater statistics

We present a general statistical analysis of Gamma Ray Bursts embedded in a
host population. If no host generates more than one observed burst, then we
show that there is a model independent lower bound on the number of hosts, $H$,
of the form $H > c B^2$, where B is the number of observed bursts, and $c$ is a
constant of order one which depends on the confidence level (CL) attached to
the bound. An analysis by Tegmark et al. (1996) shows that the BATSE 3B catalog
of 1122 bursts is consistent with no repeaters being present, and assuming that
this is indeed the case, our result implies a host population with at least
H=1.2x10^6 members. Without the explicit assumption of no repeaters, a Bayesian
analysis based on the results of Tegmark et al. (1996) can be performed which
gives the weaker bound of $H>1.7\times 10^5$ at the 90% CL. In the light of the
non-detection of identifiable hosts in the small error-boxes associated with
transient counterparts to GRBs, this result gives a model independent lower
bound to the number of any rare or exotic hosts. If in fact GRBs are found to
be associated with a particular sub-class of galaxies, then an analysis along
the lines presented here can be used to place a lower bound on the fraction of
galaxies in this sub-class. Another possibility is to treat galaxy clusters
(rather than individual galaxies) as the host population, provided that the
angular size of each cluster considered is less than the resolution of the
detector. Finally, if repeaters are ever detected in a statistically
significant manner, this analysis can be readily adapted to find upper and
lower limits on $H$.Comment: 9 pages (LaTex, aaspp4.sty); revised version includes a detailed
discussion of limits which can be set using present BATSE data; to be
published in ApJ Letter

### Wiggly Relativistic Strings

We derive the equations of motion for general strings, i.e. strings with
arbitrary relation between tension $\tau$ and energy per unit length
$\epsilon$. The renormalization of $\tau$ and $\epsilon$ that results from
averaging out small scale wiggles on the string is obtained in the general case
to lowest order in the amount of wiggliness. For Nambu-Goto strings we find
deviations from the equation of state $\epsilon \tau = {\rm constant}$ in
higher orders. Finally we argue that wiggliness may radically modify the gauge
cosmic string scenario.Comment: 10 pages, LaTeX, UFIFT-HEP-92-1

### Optical/Near-Infrared Observations of GRO J1744-28

We present results from a series of optical (g and r-band) and near-infrared
(K'-band) observations of the region of the sky including the entire XTE and
ROSAT error circles for the ``Bursting Pulsar'' GRO J1744-28. These data were
taken with the Astrophysical Research Consortium's 3.5-m telescope at Apache
Point Observatory and with the 2.2-m telescope at the European Southern
Observatory. We see no new object, nor any significant brightening of any known
object, in these error circles, with the exception of an object detected in our
8 February 1996 image. This object has already been proposed as a near-infrared
counterpart to GRO J1744-28. While it is seen in only two of our ten 8 February
frames, there is no evidence that this is an instrumental artifact, suggesting
the possibility of near-infrared flares from GRO J1744-28, similar to those
that have been reported from the Rapid Burster. The distance to the ``Bursting
Pulsar'' must be more than 2 kpc, and we suggest that it is more than 7 kpc.Comment: 21 pages, 5 JPEG plates, 2 postscript figures. This paper will appear
in the May 1, 1997 edition of the Astrophysical Journa

### Constraints on Cosmic Strings due to Black Holes Formed from Collapsed Cosmic String Loops

The cosmological features of primordial black holes formed from collapsed
cosmic string loops are studied. Observational restrictions on a population of
primordial black holes are used to restrict $f$, the fraction of cosmic string
loops which collapse to form black holes, and $\mu$, the cosmic string
mass-per-unit-length. Using a realistic model of cosmic strings, we find the
strongest restriction on the parameters $f$ and $\mu$ is due to the energy
density in $100 MeV$ photons radiated by the black holes. We also find that
inert black hole remnants cannot serve as the dark matter. If earlier, crude
estimates of $f$ are reliable, our results severely restrict $\mu$, and
therefore limit the viability of the cosmic string large-scale structure
scenario.Comment: (Plain Tex, uses tables.tex -- wrapped lines corrected), 11 pages,
FERMILAB-Pub-93/137-

### Evolution of cosmic string configurations

We extend and develop our previous work on the evolution of a network of
cosmic strings. The new treatment is based on an analysis of the probability
distribution of the end-to-end distance of a randomly chosen segment of
left-moving string of given length. The description involves three distinct
length scales: $\xi$, related to the overall string density, $\bar\xi$, the
persistence length along the string, and $\zeta$, describing the small-scale
structure, which is an important feature of the numerical simulations that have
been done of this problem. An evolution equation is derived describing how the
distribution develops in time due to the combined effects of the universal
expansion, of intercommuting and loop formation, and of gravitational
radiation. With plausible assumptions about the unknown parameters in the
model, we confirm the conclusions of our previous study, that if gravitational
radiation and small-scale structure effects are neglected, the two dominant
length scales both scale in proportion to the horizon size. When the extra
effects are included, we find that while $\xi$ and $\bar\xi$ grow, $\zeta$
initially does not. Eventually, however, it does appear to scale, at a much
lower level, due to the effects of gravitational back-reaction.Comment: 61 pages, requires RevTex v3.0, SUSSEX-TH-93/3-4,
IMPERIAL/TP/92-93/4

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