{
  "bibcode": "2007GCN..6437....1B",
  "body": "M.Biskup, M.Cwiok, W.Dominik, G.Kasprowicz, A.Majcher, A.Majczyna,\nK.Malek, L.Mankiewicz, M.Molak, K.Nawrocki, L.W.Piotrowski,\nM.Sokolowski, J.Uzycki, G.Wrochna, F.Zarnecki\non behalf of \"Pi of the Sky\" collaboration http://grb.fuw.edu.pl\n\n\"Pi of the Sky\" apparatus located at Las Campanas Observatory\nimaged the region of GRB 070521 from 6:13 UT, i.e. 38 minutes\nbefore the GRB, with 10s exposures (IR-cut filter only).\nThe most interesting exposure started at 6:51:10.9,\ni.e. exactly in coincidence with the GRB trigger.\nVariable thin clouds seriously disturbed the observations.\nNo OT was detected within the XRT error box.\n\nLimits for 10s exposures:\n6:50:44-6:50:54   >11.7\n6:50:57-6:51:07   >11.9\n6:51:10-6:51:20   >12.0 --- GRB trigger\n6:51:24-6:51:34   >12.0\n6:51:38-6:51:48   >12.2\n\nLimits for 20 coadded images\n6:42:51-6:47:17   >12.2\n6:47:21-6:51:48   >12.6\n6:51:52-6:56:18   >12.5\n6:56:22-7:00:53   >12.7",
  "circularId": 6437,
  "createdOn": 1179738954000,
  "email": "wrochna@fuw.edu.pl",
  "subject": "GRB 070521: optical limit by  Pi of the Sky",
  "submitter": "Grzegorz Wrochna at Soltan Inst.for Nuclear Studies  <wrochna@fuw.edu.pl>",
  "eventId": "GRB 070521"
}