{
  "bibcode": "2013GCN.15177....1T",
  "body": "M. Tanga, V. Sudilovsky, D. A. Kann, and J. Greiner (all MPE Garching)\nreport on behalf of the GROND team:\n\nWe re-observed (Sudilovsky et al., GCN #15170) the field of GRB 130903A\n(Mereghetti et al. 2013, GCN #15169) simultaneously in g'r'i'z'JHK with\nGROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG/ESO\ntelescope at La Silla Observatory (Chile).\n\nObservations are centered at 09:19 UT on 04 Sep 2013, 35.53 hours after\nthe GRB trigger, with a total exposure time of 50 min in g'r'i'z' and 40\nmin in JHK. They were performed at an average seeing of 1\".1 and an\naverage airmass of 1.3.\n\nIn the XRT error circle given by Grupe & Holland (GCN #15173), we detect a\nsource in our first epoch observations (Sudilovsky et al., GCN #15170) at\ncoordinates\n\nRA (J2000) = 05:28:31.33\nDec. (J2000) = -00:07:38.4\n\nwith an error of 0\".3 arcseconds.\n\nFor the first epoch, we derive preliminary magnitudes (AB system) of:\n\ng' = 22.4 +/- 0.1,\nr' = 22.2 +/- 0.1,\ni' = 22.0 +/- 0.1,\nz' = 21.7 +/- 0.1,\nJ > 21.6,\nH > 20.8, and\nK > 20.1.\n\nThe source is still detected in g'r'i'z' in the second epoch, but is seen\nto have faded by 1 mag in the r' band. We therefore conclude that this is\nthe afterglow of GRB 130903A.\n\nMagnitudes were obtained against the SDSS catalog in g'r'i'z' and against\nthe 2MASS catalog in JHK. They have not been corrected for the expected\nGalactic extinction of E(B-V) = 0.14 mag in the direction of the burst\n(Schlegel et al. 1998).",
  "circularId": 15177,
  "createdOn": 1378306961000,
  "email": "kann@tls-tautenburg.de",
  "subject": "GRB 130903A: GROND Afterglow Discovery",
  "submitter": "Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>",
  "eventId": "GRB 130903A"
}