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Дата изменения: Tue Aug 20 18:39:45 1996
Дата индексирования: Tue Oct 2 14:30:55 2012
Кодировка:
Поисковые слова: comet tail

Introduction

The observed isotropy on the sky and non-uniform spatial distribution of GRB revealed by the BATSE device onboard the Compton Gamma-Ray Observatory (e.g. Meegan et al. 1992) lend support to the idea of cosmological origin of GRB (Prilutski & Usov 1975; Usov & Chibisov 1975) for which the best candidates could be merging binary NS+NS or NS+BH at high redshifts ( ), (Blinnikov, et al. 1984; Paczynski 1991, 1992). Narayan, Paczynski & Piran (1992) argued that the rate of double NS coalescence as a result of orbital shrinking induced by gravitational waves are far from being sufficient to explain the observed properties of cosmic GRB and their rate (  bursts per day). Wickramasinghe et al (1993) showed the consistency of standard cosmology and the BATSE GRB - distribution.

The cosmological models for GRB have not yet been proven; moreover, they come across severe problems (such as no-host-galaxy limits, baryon contamination degradation of the high energy photons, efficiency problems at getting the NS binding energy out of the BH into gamma-rays etc.), which we will not address here.

However, the cosmological models involving binary NS or NS+BH coalescences must have clear observational consequences in showing the effects of binary coalescence rate evolution on the observed - distribution and . Attempts to take the intrinsic evolution of the sources into account have been carried out in a number of papers (see e.g. Piran 1992; Yi 1994; Cohen & Piran 1995), but all of them used simple ad hoc assumptions for the sources evolution.

Both the parameters of the cosmological model and source evolution are known to influence the shape of the integral statistical distributions of sources (e.g. Weinberg 1972), and it has until now been very difficult or even impossible to separate these effects from each other. This is similar to the failure of using counts of radio sources to check the cosmological models, as the evolution of number per comoving frame, spectral shape, luminosity etc is very complicated and poorly understood as yet.

In contrast, the evolution of binary systems being based and confirmed by a bulk of astronomical observations at different wavelengths is much better understood. The analysis of the evolutionary scenario of binary systems by Lipunov et al. 1995 showed that a few key parameters largely define the overall binary evolution. These parameters are the spectrum f(q) of the initial binary mass ratio and the efficiency of binary orbital momentum transfer into a common envelope. These parameters can be constrained by comparing the numbers of binaries in different stages of evolution in the Galaxy predicted by the scenario with the observed numbers (Lipunov et al. 1995).

In the present paper we compute the cumulative statistical distribution, - , and test for binary NS and NS+BH coalescence taking into account the temporal change of their rates found by Monte-Carlo modelling of the modern scenario of binary star evolution (the ``Scenario Machine'' method). A comparison of the computed distribution with that of the 2nd BATSE GRB catalogue (Meegan et al. 1994) is also made.