{
  "bibcode": "2008GCN..8547....1C",
  "body": "B. E. Cobb (UC Berkeley) reports:\n\nUsing the ANDICAM instrument on the 1.3m telescope at CTIO, we\nobtained several epochs of optical/IR imaging of the\nerror region of GRB 081121 (GCN 8537, Oates et al.).  Each\nepoch consisted of several dithered images in each filter, with\ntotal summed exposure times of 180s in each of BRIJK and 120s\nin each of H and V.\n\nAt a mid-exposure time of 2008-11-22 02:02 (5.4 hrs post-burst),\nthe GRB afterglow (GCN 8536, Yuan et al.) is detected with the\nfollowing magnitudes:\nB = 19.34 +/- 0.04\nR = 18.61 +/- 0.04\nI = 18.21 +/- 0.04\nJ = 17.21 +/- 0.15\nH = 17.05 +/- 0.15\nK = 16.75 +/- 0.15\n\nObservations were obtained under non-photometric conditions.  In optical,\nthese preliminary magnitudes are calibrated against several USNO-B1.0\nstars in the field, so there is likely an additional photometric\ncalibration error of ~0.3 magnitudes.  In the IR, calibration is against \n2MASS stars.\n\nBetween 5.4 hrs and 8.7 hours post-burst, the afterglow decays\nwith an approximate optical decay rate of alpha~-1 (where\nafterglow flux is proportional to t^alpha).",
  "circularId": 8547,
  "createdOn": 1227400069000,
  "email": "bcobb@astro.berkeley.edu",
  "subject": "GRB 081121, SMARTS optical/IR afterglow observations",
  "submitter": "Bethany Cobb at UC Berkeley  <bcobb@astro.berkeley.edu>",
  "eventId": "GRB 081121"
}