{
  "bibcode": "2006GCN..5465....1C",
  "body": "B. E. Cobb and C. D. Bailyn, part of the larger SMARTS consortium, report:\n\nUsing the ANDICAM instrument on the 1.3m telescope at CTIO, we\nobtained optical/IR imaging of the error region of GRB 060729\n(Grupe et al. GCN 5365) with the following mid-exposure times:\n        obs1 2006-08-03 10:07 UT -  4.6 days post-burst\n        obs2 2006-08-12 10:11 UT - 13.6 days post-burst\n        obs3 2006-08-14 09:26 UT - 15.6 days post-burst\n        obs4 2006-08-16 09:27 UT - 17.6 days post-burst\nFor each observation, total summed exposure times amounted to\n36 minutes in I and 30 minutes in J.\n\nThe afterglow of GRB 060729 is clearly visible in the I-band in\nour first observation (obs1), despite 4.6 days having past since the\nGRB occurred.  The preliminary afterglow magnitude is I = 20.0 +/- 0.1.\nThe I-band photometry is calibrated to a number of secondary stars in the\nfield of GRB 060729.  The magnitude of these secondary stars was\nderived using Landolt standard star observations obtained\nduring the night of obs4, which was a photometric night at CTIO.\nThe afterglow is only marginally detected in the corresponding\nJ-band image, which has an approximate limiting magnitude of J > 19\n(calibrated based on several 2MASS stars in the field).\n\nNo source appears at the position of the afterglow in the individual\nobservations taken 13.6 to 17.6 days post-burst (obs2 - obs4). \nWhen these three images are combined, however, a faint source is \ndetected in the I-band, with magnitude I = 21.9 +/- 0.2\n(no source is detected in the combined J-band image to a limiting\nmagnitude of J > 19.5).  A decay of ~2 magnitudes between day ~5\nand day ~16 is consistent with an afterglow decay rate\nof alpha ~ -1.5, but steeper than the late-time optical\ndecay noted by Grupe (GCN 5432).  If the host galaxy contributes\nsignificantly, the afterglow decay must be steeper still.",
  "circularId": 5465,
  "createdOn": 1155914120000,
  "email": "cobb@astro.yale.edu",
  "subject": "GRB 060729, SMARTS optical/IR observations",
  "submitter": "Bethany Cobb at Yale U  <cobb@astro.yale.edu>",
  "eventId": "GRB 060729"
}