760 research outputs found
A Principal Component Analysis of the 3B Gamma-Ray Burst Data
We have carried out a principal component analysis for 625 gamma-ray bursts
in the BATSE 3B catalog for which non-zero values exist for the nine measured
variables. This shows that only two out of the three basic quantities of
duration, peak flux and fluence are independent, even if this relation is
strongly affected by instrumental effects, and these two account for 91.6% of
the total information content. The next most important variable is the fluence
in the fourth energy channel (at energies above 320 keV). This has a larger
variance and is less correlated with the fluences in the remaining three
channels than the latter correlate among themselves. Thus a separate
consideration of the fourth channel, and increased attention on the related
hardness ratio appears useful for future studies. The analysis gives the
weights for the individual measurements needed to define a single duration,
peak flux and fluence. It also shows that, in logarithmic variables, the
hardness ratio is significantly correlated with peak flux, while is
significantly anticorrelated with peak flux. The principal component analysis
provides a potentially useful tool for estimating the improvement in
information content to be achieved by considering alternative variables or
performing various corrections on available measurementsComment: Ap.J., accepted 12/9/97; revised version contains a new appendix,
somewhat expanded discussion; latex, aaspp4, 15 page
Properties of the intermediate type of gamma-ray bursts
Gamma-ray bursts can be divided into three groups ("short", "intermediate",
"long") with respect to their durations. The third type of gamma-ray bursts -
as known - has the intermediate duration. We show that the intermediate group
is the softest one. An anticorrelation between the hardness and the duration is
found for this subclass in contrast to the short and long groups.Comment: In Sixteenth Maryland Astrophysics Conferenc
On the large-scale angular distribution of short-Gamma ray bursts
We investigate the large-scale angular distribution of the short-Gamma ray
bursts (SGRBs) from BATSE experiment, using a new coordinates-free method. The
analyses performed take into account the angular correlations induced by the
non-uniform sky exposure during the experiment, and the uncertainty in the
measured angular coordinates. Comparising the large-scale angular correlations
from the data with those expected from simulations using the exposure function
we find similar features. Additionally, confronting the large-angle
correlations computed from the data with those obtained from simulated maps
produced under the assumption of statistical isotropy we found that they are
incompatible at 95% confidence level. However, such differences are restricted
to the angular scales 36o - 45o, which are likely to be due to the non-uniform
sky exposure. This result strongly suggests that the set of SGRBs from BATSE
are intrinsically isotropic. Moreover, we also investigated a possible
large-angle correlation of these data with the supergalactic plane. No evidence
for such large-scale anisotropy was found.Comment: Accepted for publication in The Astrophysical Journal, 6 pages, 3
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