The afterglow of GRB 050709 and the nature of the short-hard γ-ray bursts
Cenko, S. B.; Peterson, B. A.; Price, P. A.; Harrison, F. A.; Berger, E.; Frail, D. A.; Gal-Yam, A.; Kulkarni, S. R.; Schmidt, B. P.; Chevalier, R. A.; Hurley, K. C.; Kawai, N.; Roth, M.; Watson, D.; Phillips, M. M.; Kasliwal, M. M.; Fox, D. B.; Moon, D. -S.; McCarthy, P. J.; Soderberg, A. M.; Aoki, K.; Rich, J.; Kumar, P.; Roth, K.; MacFadyen, A.; Totani, T.; Shectman, S.; Kosugi, G.; Piran, T.; Nakar, E.; Park, H. -S.; Rauch, M.; Penprase, B.; Cameron, P. B.; Cowie, L.; Lee, B. L.
Abstract
The final chapter in the long-standing mystery of the γ-ray bursts (GRBs) centres on the origin of the short-hard class of bursts, which are suspected on theoretical grounds to result from the coalescence of neutron-star or black-hole binary systems. Numerous searches for the afterglows of short-hard bursts have been made, galvanized by the revolution in our understanding of long-duration GRBs that followed the discovery in 1997 of their broadband (X-ray, optical and radio) afterglow emission. Here we present the discovery of the X-ray afterglow of a short-hard burst, GRB 050709, whose accurate position allows us to associate it unambiguously with a star-forming galaxy at redshift z = 0.160, and whose optical lightcurve definitively excludes a supernova association. Together with results from three other recent short-hard bursts, this suggests that short-hard bursts release much less energy than the long-duration GRBs. Models requiring young stellar populations, such as magnetars and collapsars, are ruled out, while coalescing degenerate binaries remain the most promising progenitor candidates.