On multiple classes of gamma-ray bursts, as deduced from autocorrelation functions or bivariate duration/hardness ratio distributions
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Date
2012
Authors
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Journal ISSN
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Publisher
Oxford University Press
Abstract
Autocorrelation functions (ACFs) of 119 gamma-ray bursts (GRBs) monitored by the Burst
Alert Telescope (BAT) on Swift are calculated. Contrasting with previous results for smaller
numbers of bursts from other missions, the widths of the ACFs are not bimodally distributed.
Although the distribution appears slightly asymmetrical, underlying mixtures of distributions
can also probably be ruled out. Factors contributing to differences between the results presented
here, and those in the literature, may include the differences in energy passbands used, and
the superior sensitivity of the BAT instrument (which affects e.g. the redshift distribution of
the detected GRB). The second part of the paper is concerned with the fitting of mixtures of
bivariate Gaussians to the joint duration/hardness ratio data of 325 GRBs. A careful analysis
confirms that a three-component mixture is the statistically most acceptable, but it is shown
that the implied marginal distribution of the hardness ratios does not fit the data very well.
It is also stressed that mixture components cannot automatically be assumed to represent
different classes of GRBs. The point is illustrated by showing two substantially different, but
statistically almost equivalent, mixture models for the distribution of 571 BAT-determined
GRB durations.
Description
Keywords
Methods: statistical, Gamma-ray burst: general
Citation
Koen, C. & Bere, A. (2012). On multiple classes of gamma-ray bursts, as deduced from autocorrelation functions or bivariate duration/hardness ratio distributions. Monthly Notices of the Royal Astronomical Society, 420: 405–415