The short-hard GRB 051103: Observations and implications for its nature

The bright short-hard GRB 051103 was triangulated by the Inter-Planetary Network and found to occur in the direction of the nearby M81/M82 galaxy group. Given its possible local-universe nature, we searched for an afterglow associated with this burst. We observed the entire 3 σ error quadrilateral using the Palomar 60 inch robotic telescope and the Very Large Array (VLA) about 3 days after the burst. We used the optical and radio observations to constrain the flux of any afterglow related to this burst and to show that this burst is not associated with a typical supernova out to z ≈ 0.15. Our optical and radio observations, along with the Konus/Wind gamma-ray energy and light curve, are consistent with this burst being a giant flare of a soft gamma-ray repeater (SGR) within the M81 galaxy group. Furthermore, we find a star-forming region associated with M81 within the error quadrilateral of this burst, which supports the SGR hypothesis. If confirmed, this will be the first case of a soft gamma-ray repeater outside the Local Group.