{
  "bibcode": "2013GCN.14401....1C",
  "body": "B. E. Cobb (GWU), reports:\n\nUsing the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained\noptical/IR imaging of the error region of GRB 130418A (GCN 14377,\nDe Pasquale et al.) at two epochs (with mid-exposure times of\n2013-04-19 00:03 UT & 01:24 UT). For each epoch, several dithered\nimages were obtained with total summed exposure times of\n15 min in V and I and 12 min in J and K.\n\nThe fading afterglow of GRB 130418A (e.g. GCN 14377, De Pasquale\net al.; GCN 14378, Gorosabel et al.; GCN 14379, Quadri et al.)\nwas detected with the following magnitudes:\n\nmid-exposure\ntime\n(hours)               V mag              I mag               J\nmag              K mag\n5.03944 hours   18.41 +/- 0.03  17.57 +/- 0.03  16.46 +/- 0.10  14.82 +/-\n0.10\n6.38972 hours   18.59 +/- 0.03  17.69 +/- 0.03  16.70 +/- 0.10  15.05 +/-\n0.10\n\n(Optical photometry is calibrated against Landolt standard stars\nand IR photometry is calibrated against a 2MASS star in the field.)\n\nBetween about 5 hrs and 6.4 hrs post-burst, the GRB afterglow fades with\na decay rate of approximately alpha = 0.6 +/- 0.2 in the optical\n(where afterglow flux is proportional to t^-alpha).",
  "circularId": 14401,
  "createdOn": 1366411266000,
  "email": "bcobb@gwu.edu",
  "subject": "GRB 130418A: SMARTS optical/IR afterglow observations",
  "submitter": "Bethany Cobb at GWU  <bcobb@gwu.edu>",
  "eventId": "GRB 130418A"
}