{
  "bibcode": "2011GCN.12356....1E",
  "body": "J. Elliott (MPE Garching), D. A. Kann (TLS Tautenburg), and J. Greiner\n(also MPE Garching) report on behalf of the GROND team:\n\nWe observed the field of the AGILE GRB 110915B (E. Del Monte et al., GCN\n12341) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,\nPASP, 120, 405) mounted at the 2.2 m MPI/ESO telescope at La Silla\nObservatory (Chile).\n\nObservations were taken starting at 06:59 UT on 18 September 2011 (2.5 days\nafter the GRB trigger). They were performed at an average seeing of 1\".4\nand at an airmass of 2, with the Moon only 22 degrees away.\n\nWe detect the afterglow candidate reported by A. de Ugarte Postigo et al.\n(GCN 12350). Based on an exposure time of 4502 s in the optical, we estimate\nan r' magnitude (in AB) of:\n\nr' = 23.2 +/- 0.1.\n\nCompared to the magnitudes reported by A. de Ugarte Postigo et al., the\ncandidate shows no decay over the past 2.1 days and so is likely not the\nGRB\nafterglow. We find a flux ratio between optical and X-rays of f_x/f_opt =\n4500 which indicates an AGN nature if the X-ray emission (P. D'Avanzo et\nal., GCN 12348) has not faded.\n\nGiven magnitudes are calibrated against GROND zeropoints and shifted based\non the USNO-B1.0 star used by A de Ugarte Postigo., RA = 05:10:09.720,\nDec. = +01:56:40.12, and are not corrected for the expected Galactic\nforeground extinction corresponding to a reddening of E(B-V) = 0.07 in the\ndirection of the burst (Schlegel et al. 1998).\n\nWe are indebted to A. de Ugarte Postigo for providing us a finding chart.",
  "circularId": 12356,
  "createdOn": 1316449414000,
  "email": "kann@tls-tautenburg.de",
  "subject": "GRB 110915B: GROND Observations of the Optical/NIR Afterglow  Candidate",
  "submitter": "Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>",
  "eventId": "GRB 110915B"
}