{
  "subject": "GRB 130831A: ISON-UAFO optical observations",
  "eventId": "GRB 130831A",
  "bibcode": "2013GCN.15185....1V",
  "createdOn": 1378596051000,
  "circularId": 15185,
  "submitter": "Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>",
  "email": "apozanen@iki.rssi.ru",
  "body": "A. Volnova (IKI), A. Matkin (UAFO, ISON), A. Stepura (UAFO, ISON), I. \nMolotov (KIAM), A. Pozanenko (IKI) report on behalf of  larger GRB \nfollow-up collaboration:\n\nWe observed the afterglow (Hagen et al., GCN  15139; Guidorzi et al., \nGCN 15140) of the Swift GRB 130831A (Hagen et al., GCN  15139) with \nSANTEL-650 (0.65m) and VT-50 (0.5m)  telescopes of UAFO/ISON-Ussuriysk \nobservatory  starting on  Aug. 31  (UT) 13:14:32, i.e. 10.3  minutes \nafter burst trigger.  We took unfiltered  images of 120s and 30s \nexposures  ending observations at (UT) 19:20:53.\n\nIn each initial frames we clearly detect afterglow. A preliminary \nphotometry of the afterglow in the initial frames are following\n\nT_start              T0+       Filter, Exposure, OT,    OT_err\n(UT)                 (mid, d)            (s)\n\n2013-08-31T13:14:32  0.00782   none    120       13.86  0.02\n2013-08-31T13:l6:40  0.00931   none    120       13.75  0.02\n2013-08-31T13:18:49  0.01080   none    120       13.78  0.02\n\nThe photometry is based on reference stars SDSS-DR9, (R mag, \ntransformation by Lupton 2005)\n\nN\tSDSS id\t\t\tR(Lupton)errR\n1\tJ235443.71+292539.3\t13.491\t 0.016\n2\tJ235438.60+292547.3\t14.136\t 0.015\n3\tJ235423.64+292452.8\t17.120\t 0.016"
}