{
  "bibcode": "2012GCN.13729....1S",
  "body": "V. Sudilovsky (MPE Garching), S. Schmidl (TLS Tautenburg), D.A. Kann (MPE\nGarching) and J. Greiner (MPE Garching) report on behalf of the GROND\nteam:\n\nWe observed the field of GRB 120909A (Swift trigger 533060; Immler et al.,\nGCN #13727) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,\nPASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla\nObservatory (Chile).\n\nObservations started at 01:44 UT, September 09, 140s after the burst, and\nare continuing. They were performed at an average seeing of 1\".6 and at an\naverage airmass of 1.2 .\n\nWe found a single point source within the 4\".8 Swift-XRT error circle\nreported by Immler et al. (GCN #13727) at\n\nRA (J2000.0) = 18h 22m 56.72s\n\nDEC (J2000.0) = -59d 26' 54\".1\n\nwith an uncertainty of 0\".5 in each coordinate, which is consistent with\nthe position reported by Haislip et al. (GCN #13728)   .\n\nBased on the first 141s of total exposures in g'r'i'z' and 240s in JHK,\nwe estimate preliminary magnitudes (all in AB) of\n\ng' = 18.4 +- 0.1,\nr' = 16.6 +- 0.1,\ni' = 15.8 +- 0.1,\nz' = 15.5 +- 0.1,\nJ = 14.8 +- 0.1,\nH = 14.5 +- 0.1, and\nK = 14.3 +- 0.1.\n\nBased on the the significantly lower flux in g', this suggests a \nredshift z>3.\n\nGiven magnitudes are calibrated against GROND zeropoints as well as 2MASS\nfield stars and are not corrected for the expected Galactic foreground\nextinction corresponding to a reddening of E_(B-V)=0.08 mag in the\ndirection of the burst (Schlegel et al. 1998).",
  "circularId": 13729,
  "createdOn": 1347158497000,
  "email": "vsudilov@mpe.mpg.de",
  "subject": "GRB 120909A: GROND detection of the afterglow",
  "submitter": "Vladimir Sudilovsky at MPE  <vsudilov@mpe.mpg.de>",
  "eventId": "GRB 120909A"
}