Analysis of Fermi gamma-ray burst duration distribution

Abstract

Two classes of GRBs, short and long, have been determined without any doubts, and are usually prescribed to different physical scenarios. A third class, intermediate in $T_{90}$ durations, has been reported to be present in the datasets of BATSE, Swift, RHESSI and possibly BeppoSAX. The latest release of $>1500$ GRBs observed by Fermi gives an opportunity to further investigate the duration distribution. The aim of this paper is to investigate whether a third class is present in the $\log T_{90}$ distribution, or is it described by a bimodal distribution. A standard ${\chi }^2$ fitting of a mixture of Gaussians is applied to 25 histograms with different binnings. Different binnings give various values of the fitting parameters, as well as the shape of the fitted curve. Among five statistically significant fits none is trimodal. Locations of the Gaussian components are in agreement with previous works. However, a trimodal distribution, understood in the sense of having three separated peaks, is not found for any binning. It is concluded that the duration distribution in Fermi data is well described by a mixture of three log-normal distributions, but it is intrinsically bimodal, hence no third class is present in the $T_{90}$ data of Fermi. It is suggested that the log-normal fit may not be an adequate model.

6 pages, 3 figures; matches the version to be published

References in corpus (6)

• Further Study of the Gamma-Ray Bursts Duration Distribution
• Classification of Swift's gamma-ray bursts
• An analysis of the durations of Swift Gamma-Ray Bursts
• Statistical Study of Observed and Intrinsic Durations among BATSE and Swift/BAT GRBs
• Classification of BeppoSAX's Gamma-Ray Bursts
• Analysis of the Swift Gamma-Ray Bursts duration

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