Friday, June 21, 2013

1306.4971 (N. R. Tanvir et al.)

A search for kilonova emission associated with GRB 130603B: the smoking gun signature of a compact binary merger event    [PDF]

N. R. Tanvir, A. J. Levan, A. S. Fruchter, J. Hjorth, K. Wiersema, R. Tunnicliffe, A. de Ugarte Postigo
The nature of short duration gamma-ray bursts (S-GRBs) represents one of the great unsolved mysteries of astrophysics today. While a favoured model for their origin is the merger of two compact objects (e.g., neutron stars) this lacks a smoking gun signature to date. However, these mergers are expected to create radioactive species, including heavy r-process elements, which should result in a faint, fast transient in the days following the burst, a so-called kilonova. Recent calculations suggest much energy comes out in the near-infrared in the days following the initial burst. Here we report a search for such an event accompanying GRB 130603B, the first S-GRB to have a firm redshift established directly from the afterglow. At z=0.36 the faint transient is expected to peak a few days after the burst at an H-band magnitude of ~25. Observing with the Hubble Space Telescope (HST) nine days post-burst, we indeed find a source at the location of the burst, with these properties, although we cannot yet say whether the light is transient in nature. If it is kilonova emission, then it provides both strong support for the binary neutron star merger theory of short-GRBs and an alternative, un-beamed electromagnetic signature of the most promising gravitational wave sources. We note that we felt compelled to submit this provisional report of our work, despite our HST DDT program being incomplete, due to other authors having already posted an analysis of the publicly available first epoch data.
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