{
  "bibcode": "2011GCN.11642....1L",
  "body": "A.J. Levan (U. Warwick), N.R. Tanvir (U. Leicester) report for a\nlarger collaboration:\n\nWe obtained imaging of GRB 101225A (Racusin et al. GCN 11493)  with\nGMOS on Gemini North on 5 Feb 2011. At this epoch we obtained a\ntotal of 2400s in a narrow band H-alpha filter (centered a z~0) and\n900s in the r-band.\n\nThe afterglow is weakly detected in the H-alpha image, but not in the\ncontemporaneous r-band imaging. This suggests substantial spectral\nevolution from the early-time spectroscopy (Chornock et al. GCN\n11507), and that line emission is now contributing significantly\nto the emission between 6000-7000A.\n\nGiven the absence of any host galaxy, and the extremely unusual\ncharacteristics of this event, the most natural explanation is that\nwe are detecting Ha at z~0 from some class of high-energy\ntransient. If that is the case, three possible locations seem most\nlikely:\n\n(a) it could be a source within the Milky Way, sufficiently far\naway that the progenitor was undetected in prior imaging,\n\n(b) it could be in the far halo of M31 at a distance of at least\n~115 kpc\n\n(c) it could be associated with the distant Local Group dwarf\nspheroidal galaxy Andromeda XVIII, which itself is located ~1.4 Mpc\nfrom us, but is only ~12 kpc from the line of sight to 101225A.\n\nWe note that the early optical and X-ray emission (in particular\nthe ratio of the two) remain extremely unusual for known Galactic \ntransients.\n\nWe thank the staff of Gemini North for the rapid and effective\nexecution of these observations.",
  "circularId": 11642,
  "createdOn": 1296903156000,
  "email": "A.J.Levan@warwick.ac.uk",
  "subject": "GRB 101225A is likely at z~0",
  "submitter": "Andrew Levan at U.of Leicester  <A.J.Levan@warwick.ac.uk>",
  "eventId": "GRB 101225A"
}