{
  "bibcode": "2011GCN.12588....1B",
  "body": "E. Berger, W. Fong (Harvard), T. Sakamoto (GSFC/UMBC), and E. Troja\n(NASA/GSFC/ORAU) report:\n\n\"We re-analyzed the Chandra observation of the short GRB 111117A (Sakamoto\net al. GCN 12580) for the purpose of clarifying and refining the astrometry\nrelative to the location of the host galaxy (using an optical image from\nMagellan/IMACS:  Fong et al. GCN 12566).  Using 4 objects in common to the\nChandra data and the IMACS image (which is itself tied to USNO-B with 0.25\"\nrms) we find a correction to the native Chandra astrometry of:\n\ndRA = -0.54+/-0.17\"\ndDEC = +0.34+/-0.14\"\n\nsubstantially improved relative to the 0.6\" systematic uncertainty of the\nnative Chandra astrometry (Sakamoto et al. GCN 12580).  With this\ncorrection, the position of the X-ray counterpart of GRB 111117A is (J2000):\n\nRA = 00:50:46.257\nDEC = +23:00:40.01\n\nwith a statistical uncertainty of about 0.13\" in each coordinate.\n\nRelative astrometry compared to the centroid of the host galaxy indicates a\nprojected angular offset of 1.0\".  Although the redshift of the host galaxy\nis not known at the present, this roughly corresponds to 6-8 kpc at\nredshifts of z>0.5 (typical of short GRB offsets: Fong et al. 2010, ApJ,\n708, 9).\"",
  "circularId": 12588,
  "createdOn": 1322081922000,
  "email": "eberger@cfa.harvard.edu",
  "subject": "GRB 111117A: Refined Chandra Astrometry",
  "submitter": "Edo Berger at Harvard  <eberger@cfa.harvard.edu>",
  "eventId": "GRB 111117A"
}