{
  "bibcode": "2010GCN.11020....1O",
  "body": "F. Olivares, T. Kruehler, R. Filgas, J. Greiner, M. Nardini (all MPE\nGarching) and A. Nicuesa (TLS Tautenburg) report on behalf of the GROND\nteam:\n\nWe observed the field of GRB 100728A (Swift trigger 430151; Cannizzo et\nal., GCN #11004; A. von Kienlin, GCN #11006) simultaneously in\ng'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at\nthe 2.2 m MPI/ESO telescope at La Silla Observatory (Chile).\n\nObservations started at 09:26 UT, 7 hours after the GRB trigger and were\nterminated at 10:32 UT by the GRB 100728B trigger. They\nwere performed at an average seeing of 1.3\" and at an average airmass of\n2.5.\n\nWe found a single, very faint point source in the H band within the\nenhanced Swift-XRT error circle reported by Beardmore et al. (GCN #11005) at\n\nRA (J2000.0) = 05:55:02.01\nDEC (J2000.0) = -15:15:20.4\n\nwith an uncertainty of 0.5\" in each coordinate.\n\nBased on 24 min of total exposures in g'r'i'z' JHK, we\nestimate preliminary magnitudes and upper limits (all in AB system) of\n\ng' > 23.3\nr' > 23.9\ni' > 23.5\nz' > 23.5\nJ > 22.0\nH = 21.2 +- 0.3\nK > 20.3\n\nGiven magnitudes and upper limits are obtained by calibrating the images\nagainst GROND zeropoints as well as 2MASS field stars and are not\ncorrected for the expected Galactic foreground extinction corresponding\nto a reddening of E_(B-V)=0.18 mag in the direction of the burst\n(Schlegel et al. 1998).\n\nThese magnitudes imply very red colors of the afterglow of J-H > 0.8\nand r-H > 2.7. Together with the significant excess absorption seen by\nthe XRT (Evans & Cannizzo, GCN 11014), and the lack of prompt detections\nin the optical and UV filters (Oates & Cannizzo, GCN 11016), these values\nare suggestive of a highly extinguished optical/NIR afterglow. The K band\nupper limit is not constraining even for the steepest SED slopes and\nconsistent with this hypothesis.",
  "circularId": 11020,
  "createdOn": 1280336150000,
  "email": "filgas@mpe.mpg.de",
  "subject": "GRB 100728A: GROND Detection of the NIR Afterglow Candidate",
  "submitter": "Robert Filgas at MPI  <filgas@mpe.mpg.de>",
  "eventId": "GRB 100728A"
}