{
  "bibcode": "2007GCN..6757....1P",
  "body": "D. A. Perley,  J. S. Bloom (UC Berkeley),  and C. C. Thoene (DARK, UCB)\nreport:\n\nBeginning at 06:48:00 UT (2007-08-11) we began a second series of imaging\nexposures on the field of GRB 070810A (GCN 7433) using the Keck I\ntelescope (+LRIS).  We acquired a total of 390s in R band and 480s in g\nband through high airmass.\n\nThe optical afterglow (GCN 6734) is still detected, but has faded\nsignificantly since our previous imaging epoch (GCN 6741) and appears\nmarginally extended.  Aperture photometry of the source indicates that it\nhas has faded by 3.2 +/- 0.1 magnitudes since the observations the first\nnight, corresponding to a decay index of alpha >= 1.5 between 4 hours and\n28.6 hours including a possible contribution from a host galaxy or other\nextended source.\n\nUsing the same calibration system as in our previous circular, we estimate\na preliminary magnitude of R=23.7.",
  "circularId": 6757,
  "createdOn": 1186895292000,
  "email": "dperley@astro.berkeley.edu",
  "subject": "GRB 070810A: Continued Keck Imaging",
  "submitter": "Daniel Perley at U.C. Berkeley  <dperley@astro.berkeley.edu>",
  "eventId": "GRB 070810A"
}