{
  "bibcode": "2008GCN..8046....1L",
  "body": "W. Li, R. Chornock, D. A. Perley, J. S. Bloom, and A. V. Filippenko,\nUniversity of California at Berkeley, on behalf of the KAIT GRB team;\nD. A. Kann, TLS Tautenburg, report:\n\nWe have analyzed the KAIT observations of the OA of GRB 080727B\nas reported in Li et al. (GCN 8024). The imaging sequence started\nwith 10 x 2 s unfiltered exposures, with the OA detected on each\nframe. A series of 20 s V, I, and unfiltered images were then \nobtained, and the OA was detected in the first couple of I and\nunfiltered images. Additional photometry (calibrated to USNO B1):\n\nUT start  exptime  filter     mag     err\n\n08:14:46  2  s      clear   18.98    0.28\n08:16:03  20 s      clear   19.64    0.07\n08:17:35  20 s      clear   20.68    0.23 \n\nOur GRB pipeline used more than 100 USNO B1 stars in calculating the\nphotometric zero point. However, we suspect that the USNO B1 calibration\nfor the GRB field may be significantly off.  Based on our experience in\nthe limiting magnitude of the KAIT 2 s and 20 s unfiltered images, we\nestimate that the above photometry and those reported in GCN 8024 should\nbe made brighter by 1.0 - 2.0 mag.  The corrected KAIT photometry, together\nwith the REM NIR detection (D'Avanzo et al. GCN 8037), suggests an\noptical - NIR color of R-H (Vega)  = 1.2 to 2.2 mag, which is consistent\nwith the SED fit from the GROND observations (predicted R-H (AB) = 1.0 mag;\nKruehler et al. GCN 8045).  \n\nThe KAIT unfiltered light curve of GRB 080727B can be well fit by\na broken power-law with an index of 1.08 +/- 0.07 between t = 49 s\nto 169 s, and 1.88 +/- 0.21 between t= 169 s and 524 s. Such an\nearly break in the light curve is quite extraordinary. \n\nWe plan to obtain photometric calibrations of the GRB field in the\nupcoming photometric nights at Lick Observatory.",
  "circularId": 8046,
  "createdOn": 1217288950000,
  "email": "weidong@astron.berkeley.edu",
  "subject": "GRB 080727B: KAIT photometry and an early lightcurve break",
  "submitter": "Weidong Li at UC Berkeley KAIT/LOSS  <weidong@astron.berkeley.edu>",
  "eventId": "GRB 080727B"
}