next previous
Up: Stellar evolution, GRB and


1 Motivation


The binary neutron star mergers ( Blinnikov et al. 1994; Paczynski1991) are one of the most probable GRB progenitors. Several works were devoted to fitting the observed parameters of GRB (mainly, $\log N - \log P$ distributions) by evolutionary models (e.g. Fenimore et al. 1993; Jørgensenet al. 1995; Totani 1997; Bagot et al. 1998). It is often supposed in such calculations that the merger rate is proportional to the star formation rate.

However, the coalescence time of the NS+NS and NS+BH binaries can be very long, and some of the mergers should take place in rather old stellar population, even in elliptical galaxies where there should be no noticeable star formation. This property can help to distingwish the binary merger GRB from the GRB from massive star collapses.

  
\begin{figure}

\includegraphics [width=7cm,clip]{R76_f1a.eps}

\hspace*{4mm}

\...
 ...graphics [width=7cm,clip]{R76_f1b.eps}

\vspace*{-1mm}\vspace*{-2mm}\end{figure} Figure 1: Coalescence time distributions for different kick velocities normalized for a sample galaxy with instantaneous star formation of $10^{11}M_\odot$.Left: NS+NS. Right: NS+BH
  
\begin{figure}

\includegraphics [width=7cm,clip]{R76_f2a.eps}

\hspace*{4mm}

\...
 ...graphics [width=7cm,clip]{R76_f2b.eps}

\vspace*{-1mm}\vspace*{-2mm}\end{figure} Figure 2: The ratio of the coalescence rates in spiral and elliptical galaxies at different redshift for different kick velocities. a) Left panel: NS+NS. b) Right panel: NS+BH



next previous
Up: Stellar evolution, GRB and

Copyright The European Southern Observatory (ESO)