On the difference between the short and long gamma-ray bursts

¹ Konkoly Observatory, Budapest, Box 67, 1525, Hungary
² Laboratory for Information Technology, Eötvös University, Budapest, Pázmány Péter sétány 1/A, 1117, Hungary e-mail: bagoly@ludens.elte.hu
³ Dept. of Physics, Bolyai Military University, Budapest, Box 12, 1456, Hungary e-mail: hoi@bjkmf.hu
⁴ Astronomical Institute of the Charles University, 180 00 Prague 8, V Holešovičkách 2, Czech Republic e-mail: meszaros@mbox.cesnet.cz
⁵ Dept. of Astronomy & Astrophysics, Pennsylvania State University, 525 Davey Lab e-mail: nnp@astro.psu.edu

Corresponding author: L. G. Balázs, balazs@konkoly.hu

Received: 29 August 2002
Accepted: 16 December 2002

Abstract

We argue that the distributions of both the intrinsic fluence and the intrinsic duration of the γ-ray emission in gamma-ray bursts from the BATSE sample are well represented by log-normal distributions, in which the intrinsic dispersion is much larger than the cosmological time dilatation and redshift effects. We perform separate bivariate log-normal distribution fits to the BATSE short and long burst samples. The bivariate log-normal behaviour results in an ellipsoidal distribution, whose major axis determines an overall statistical relation between the fluence and the duration. We show that this fit provides evidence for a power-law dependence between the fluence and the duration, with a statistically significant different index for the long and short groups. We discuss possible biases, which might affect this result, and argue that the effect is probably real. This may provide a potentially useful constraint for models of long and short bursts.