Observational prospects for afterglows of short-duration gamma-ray bursts

If the efficiency for producing gamma rays is the same in short-duration (less than or similar to2 s) gamma-ray bursts (GRBs) as in long-duration GRBs, then the average kinetic energy per solid angle in short GRBs must be similar to 20 times less than that of long GRBs. Assuming that the relativistic shocks in short- and long-GRB afterglows have similar parameters, we show that the afterglows of short GRBs will be, on average, 10-40 times dimmer than those of long GRBs. We find that the afterglow of a typical short GRB will be below the detection limit (less than or similar to 30 mu Jy) of searches at radio frequencies. The afterglow would also be difficult to observe in the optical, where we predict R greater than or similar to 23 10 hr the burst. The radio and optical afterglows would be even fainter if short GRBs occurred in a low-density medium, as expected in neutron star-neutron star and neutron star-black hole merger models. Early (less than or similar to1 day) observations in X-rays offer the best prospects for detecting short- GRB afterglows.