GRB 060505: A Possible Short‐Duration Gamma‐Ray Burst in a Star‐forming Region at a Redshift of 0.09

Abstract

On 2006 May 5, a 4 s duration, low-energy, ~1049 erg, gamma-ray burst (GRB) was observed, spatially associated with a z=0.0894galaxy. Here we report the discovery of the GRB optical afterglow andobservations of its environment using Gemini South, the Hubble SpaceTelescope (HST), Chandra, Swift, and the Very Large Array. The opticalafterglow of this GRB is spatially associated with a prominentstar-forming region in the Sc-type galaxy 2dFGRS S173Z112. Its proximityto a star-forming region suggests that the progenitor delay time, frombirth to explosion, is smaller than ~10 Myr. Our HST deep imaging rulesout the presence of a supernova brighter than an absolute magnitude ofabout -11 (or -12.6 in the case of maximal extinction) at about 2 weeksafter the burst and limits the ejected mass of radioactive56Ni to be less than about 2×10-4Msolar (assuming no extinction). Although it was suggestedthat GRB 060505 may belong to a new class of long-duration GRBs with nosupernova, we argue that the simplest interpretation is that thephysical mechanism responsible for this burst is the same as that forshort-duration GRBs.