Radio Detection of Old GRB Remnants in the Local Universe

Abstract

We investigate the hydrodynamic evolution of Gamma--Ray Burst (GRB) remnants at late times (>> 1 year), by extending the standard fireball model into the nonrelativistic Sedov--Taylor regime. We calculate the associated synchrotron luminosity as a function of remnant age. The radio luminosity of old remnants depends strongly on the power-law index p= (dlogN/dlogE) of the kinetic energy distribution of shock-accelerated electrons. In addition, the detection probability of remnants in nearby galaxies depends on the GRB rate in the local universe. We predict that if p<2.6 and the BATSE-calibrated GRB rate per comoving volume is independent of redshift (despite the strong evolution in the cosmic star formation rate) then the VLA can discover a 10^3 years-old GRB remnant in the Virgo cluster. Nearby GRB remnants could be searched for and resolved at radio frequencies, and then identified as distinct from supernova remnants based on the detection of the extended emission of high-ionization lines in follow--up optical observations.