2007MNRAS.378.1439L

We investigate the origin of the GRB060912A, which has observational properties that make its classification as either a long or short burst ambiguous. Short-duration gamma-ray bursts (SGRBs) are thought to have typically lower energies than long-duration bursts, can be found in galaxies with populations of all ages and are likely to originate from different progenitors to the long-duration bursts. However, it has become clear that duration alone is insufficient to make a distinction between the two populations in many cases, leading to a desire to find additional discriminators of burst type. GRB060912A had a duration of 6s and occurred only ∼10arcsec from a bright, low-redshift (z = 0.0936) elliptical galaxy, suggesting that this may have been the host, which would favour it being a short burst. However, our deep optical imaging and spectroscopy of the location of GRB060912A using the Very Large Telescope (VLT) shows that GRB060912A more likely originates in a distant star-forming galaxy at z = 0.937, and is most likely a long burst. This demonstrates the risk in identifying bright, nearby galaxies as the hosts of given gamma-ray bursts (GRBs) without further supporting evidence. Further, it implies that, in the absence of secure identifications, `host' type, or more broadly discriminators that rely on galaxy redshifts, may not be good indicators of the true nature of any given GRB.