Astron. Astrophys. 323, 312-316 (1997)

The distance scale of cosmological -ray bursts ^*

D.M. Wei ¹ and T. Lu <sup>3, 2

1</sup> Purple Mountain Observatory, Academia Sinica, Nanjing 210008, P.R. China
² Department of Astronomy, Nanjing University, Nanjing 210093, P.R. China
³ CCAST(World Laboratory) P.O.Box.8730, Beijing 100080, P.R.China

Received 18 June 1996 / Accepted 23 September 1996

Abstract

The isotropic but radially non-uniform distribution of -ray bursts (GRBs) observed with the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO) suggests that the bursts may be at cosmological distances. At such distances, the expansion of the Universe should have two main effects on the statistics of -ray bursts: first, it should stretch the temporal structure, resulting in dimmer bursts to be longer than bright bursts; second, it would decrease the number of -ray bursts with distance, resulting in the value of to be smaller than 0.5. Here we have used the observed time dilation () to estimate the distance of -ray bursts, and then we use another method, calculating the value of to obtain the distance of -ray bursts. These two methods are independent and should be self-consistent. Our results show that the redshift of the dimmest bursts determined from these two distinct methods are consistent, , corresponding to a burst luminosity of , which is different from the results reported previously.

Key words: cosmology: theory fl rays: bursts

* Supported by the National Natural Science Foundation, the National Climbing Programme on Fundamental Researches, the Foundation of the Committee for Education of China and China Postdoctoral Science Foundation

Send offprint requests to: Tan , Dept. of Astronomy, Nanjing University, Nanjing, 210093, China (tlu@nju.edu.cn)

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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