{
  "bibcode": "2009GCN..9458....1R",
  "body": "A. Rossi (Tautenburg), F. Olivares, and J. Greiner (both MPE Garching)\nreport on behalf of the GROND team:\n\nWe observed the field of GRB 090530 (Swift trigger 353567, Cannizzo et al.,\nGCN #9438) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m\nMPI/ESO telescope at La Silla Observatory (Chile). Observations started on\n31 May 2009 at 00:36 UT, 21.3 h after the burst.\n\nWe detect the optical/NIR afterglow (Cannizzo et al., GCN #9438;\nFlewelling et al., GCN #9439; Morgan et al., GCN #9440; Nissinen & Hentunen,\nGCN #9442) in stacked exposures of 20 min in JHK and 24 min in g'r'i'z'. \n\nCalibrating the r' band data against the USNO star at RA = 11:57:41.7, \nDec = +26:35:43, we obtain R = (22.2 +-0.2) mag. Comparing this with \nthe white light magnitudes obtained by ROTSE (Flewelling et al., GCN #9439),\nUVOT (Schady et al., GCN #9450) and GRAS002 (Nissinen & Hentunen,\nGCN #9442) as well as the NOT R-band magnitude (Malesani et al., GCN #9452),\nwe find a break in the optical light at around 22 ksec post-burst (i.e.\nbefore the NOT observation), with slopes of 0.5+-0.1 (pre-break) and \n1.8+-0.4 (post-break).  We note that a break at this time is also visible\nin the Swift/XRT data (see repository; Evans et al. 2007).",
  "circularId": 9458,
  "createdOn": 1243773408000,
  "email": "jcg@mpe.mpg.de",
  "subject": "GRB 090530: break in light curve",
  "submitter": "Jochen Greiner at MPI  <jcg@mpe.mpg.de>",
  "eventId": "GRB 090530"
}