124 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 New Measure of the Clustering of QSO Heavy-Element Absorption-Line Systems
We examine the line-of-sight clustering of QSO heavy-element absorption-line
systems, using a new measure of clustering, called the reduced second moment
measure, that directly measures the mean over-density of absorbers. While
closely related to other second-order measures such as the correlation function
or the power spectrum, this measure has a number of distinct statistical
properties which make possible a continuous exploration of clustering as a
function of scale. From a sample of 352 C IV absorbers with median redshift
2.2, drawn from the spectra of 274 QSOs, we find that the absorbers are
strongly clustered on scales from 1 to 20 Mpc. Furthermore, there appears to be
a sharp break at 20 Mpc, with significant clustering on scales up to 100 Mpc in
excess of that which would be expected from a smooth transition to homogeneity.
There is no evidence of clustering on scales greater than 100 Mpc. These
results suggest that strong C IV absorbers along a line of sight are indicators
of clusters and possibly superclusters, a relationship that is supported by
recent observations of ``Lyman break'' galaxies.Comment: 13 pages (LaTex, uses aaspp4.sty and psfig.sty), with 3 encapsulated
PostScript figures. To appear in The Astrophysical Journal. Extended new
discussion of the statistical properties of the reduced second moment
measure, and a new figure highlighting the excess clustering on comoving
scales greater than 20 Mp
Gravitational Lensing and the Hubble Deep Field
We calculate the expected number of multiply-imaged galaxies in the Hubble
Deep Field (HDF), using photometric redshift information for galaxies with m_I
< 27 that were detected in all four HDF passbands. A comparison of these
expectations with the observed number of strongly lensed galaxies constrains
the current value of Omega_m-Omega_Lambda, where Omega_m is the mean mass
density of the universe and Omega_Lambda is the normalized cosmological
constant. Based on current estimates of the HDF luminosity function and
associated uncertainties in individual parameters, our 95% confidence lower
limit on Omega_m-Omega_Lambda ranges between -0.44, if there are no strongly
lensed galaxies in the HDF, and -0.73, if there are two strongly lensed
galaxies in the HDF. If the only lensed galaxy in the HDF is the one presently
viable candidate, then, in a flat universe (Omega_m+Omega_Lambda=1),
Omega_Lambda < 0.79 (95% C.L.). These limits are compatible with estimates
based on high-redshift supernovae and with previous limits based on
gravitational lensing.Comment: 4 pages (aipproc.sty), 2 figures. To appear in "After the dark ages:
when galaxies were young," proceedings of the 9th Annual October Astrophysics
Conference, eds. S. S. Holt & E. P. Smit
Non-divergence of gravitational self-interactions for Goto-Nambu strings
The classical linearised gravitational self interaction of a Goto-Nambu
string is examined in four spacetime dimensions. Using a conveniently gauge
independent tensorial treatment, the divergent part of the self-force is shown
to be exactly zero. This is due to cancelation by a contribution that was
neglected in the previous treatments. This result has implications for many
applications.Comment: 7 Pages. Final version to be published in Phys. Lett. B
Match Probability Statistics and Gamma Ray Burst Recurrences in the BATSE Catalog
We develop match probability statistics to test the recurrences of gamma ray
bursts in the BATSE catalog 1B and 2B. We do not find a signal of repetitions
at the match level of 1.e-3.Comment: 4 pages, LaTeX, two macros included (kluwer.sty, spacekap.sty) To
appear in the proceedings of the Eslab29 symposium, ``gamma ray bursts:
toward the source
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