Optical emission from GRB 050709: a short/hard GRB in a star-forming galaxy

COVINO, S.; MALESANI, D.; ISRAEL, G. L.; D'AVANZO, P.; ANTONELLI, L. A.; CHINCARINI, G.; FUGAZZA, D.; CONCIATORE, M. L.; DELLA VALLE, M.; FIORE, F.; GUETTA, D.; HURLEY, K.; LAZZATI, D.; STELLA, L.; TAGLIAFERRI, G.; VIETRI, M.; CAMPANA, S.; BURROWS, D. N.; D'ELIA, V.; FILLIATRE, P.; GEHRELS, N.; GOLDONI, P.; MELANDRI, A.; MEREGHETTI, S.; MIRABEL, I. F.; MORETTI, A.; NOUSEK, J.; O'BRIEN, P. T.; PELLIZZA, L. J.; PERNA, R.; PIRANOMONTE, S.; ROMANO, P.; ZERBI, F. M.

ASTRONOMY AND ASTROPHYSICS

EDP Sciences

Lugar: Les Ulis, Francia; Año: 2006 vol. 447 p. 5 - 8

0004-6361

We present optical observations of the short/hard gamma-ray burst GRB 050709, the first such event with an identified optical counterpart. The object is coincident with a weak X-ray source and is located inside a galaxy at redshift z = 0.1606 ± 0.0002. Multiband photometry allowed us to study the broad-band spectral energy distribution. Late-time monitoring places strong limits on any supernova simultaneous with the GRB. The host galaxy is not of early type. Spectra show that the dominant stellar population is relatively young (˜ 1 Gyr), and that ongoing star formation is present at a level of 2--3 L/L_*~M_o yr-1. This is at least 2 orders of magnitude larger than that observed in the elliptical hosts of the short GRB 050509B and GRB 050724. This shows that at least some short GRBs originate in a young population. Short/hard GRB models based on the merger of a binary degenerate system are compatible with the host galaxy characteristics, although there is still the possibility of a connection between young stars and at least a fraction of such events.