{
  "bibcode": "2007GCN..6844....1L",
  "body": "W. Li, R. Chornock, A. V. Filippenko, D. A. Perley, J. S. Bloom (University\nof California, Berkeley), on behalf of the KAIT GRB team, report:\n\nWe have analyzed the KAIT observations of the GRB 071003 optical \nafterglow (OA) reported by Li (GCN 6838) and confirmed by Cenko\nand Fox (GCN 6839). Our preliminary unfiltered light curve, calibrated\nwith USNO B1.0, shows two potential breaks for the OA in the first\n10 minutes after the burst. We measured a steep power law index of \n-1.52 +/- 0.06 between t = 0.7 min and 1.2 min after the burst (from\n5 x 5s images), possibly signaling the detection of the optical reverse\nshock emission from the GRB. A shallower power law index of -0.89\n+/- 0.03 is measured between t = 1.2 min and 4.3 min (from 3 images),\nsuggesting a break in the light curve between t = 1.2 min to 2.8 min. \nThe second potential break occurred at about 4 minutes after the burst,\nwith the power law decay index measured as -1.85 +/- 0.10 from 3 images\nobserved between t = 4.3 min to 7.4 min. We note this power law decay\nindex is consistent with the value reported by Swan et al. (GCN 6841)\nat later times. Our observations ended at about 27 minutes after the\nburst due to physical limits of KAIT.  The analysis of all the data is\nstill ongoing.\n\nThe overall behavior of the OA of GRB 071003 OA is similar to that of\nGRB 061126 (Perley et al., astro-ph/0703538), but with the breaks\noccurring at an earlier stage of the evolution.  We expect contamination\nfrom the nearby bright star as discussed by Li (GCN 6838), Cenko and Fox\n(GCN 6839), and Misra et al. (GCN 6840) to slightly affect the above\npower indices, but not the overall photometric behavior.\n\nSome selected KAIT unfiltered photometry:\n\nt_start(s)     Exptime(s)     Mag     Mag(err)\n\n 42            5.000        12.83   0.02\n 67            5.000        13.56   0.03\n249           20.000        14.82   0.03\n431           20.000        15.89   0.06\n\nThis message may be cited.",
  "circularId": 6844,
  "createdOn": 1191453294000,
  "email": "weidong@astron.berkeley.edu",
  "subject": "GRB 071003: OA power-law decay indices from KAIT",
  "submitter": "Weidong Li at UC Berkeley KAIT/LOSS  <weidong@astron.berkeley.edu>",
  "eventId": "GRB 071003"
}