{
  "bibcode": "2014GCN.15650....1P",
  "body": "D. A. Perley (Caltech) reports on behalf of a larger collaboration:\n\nWe imaged the location of GRB 131231A with the Palomar 60-inch (P60) \nrobotic telescope on UT 2014-01-01 between 03:28:31 and 04:22:05, and \nagain on 2014-01-02 between 01:56:28 and 02:37:12. Observations were \ntaken in the g, r, i, and z filters during each epoch.\n\nThe afterglow (Xu et al., GCN 15641) is well-detected in individual \nexposures in all bands.  Both nights were photometric and we calibrated \nthe field using an observation of the nearby standard field SA92.\n\nSome photometry of the GRB afterglow in the gri bands (all on the \nSDSS/AB system) is:\n\nr = 18.84 +/- 0.02  (t = 0.965 d)\ni = 18.72 +/- 0.02  (t = 0.970 d)\ng = 19.14 +/- 0.02  (t = 0.982 d)\n\nr = 19.77 +/- 0.03  (t = 1.886 d)\ni = 19.64 +/- 0.04  (t = 1.893 d)\ng = 20.06 +/- 0.03  (t = 1.907 d)\n\nThe power-law temporal decay index in all bands is approximately alpha=1.3.\n\n\nWe also give gri magnitudes of the five nearby calibration stars \npresented by Halpern (GCN 15646) for reference:\n\nstar  RA          dec       R         g      r      i\n  A    00:42:30.4 -01:36:13  16.07     16.86  16.28  16.11\n  B    00:42:11.7 -01:37:29  17.95     19.50  18.24  17.66\n  C    00:42:15.9 -01:39:08  17.92     19.16  18.20  17.85\n  D    00:42:20.0 -01:41:53  17.22     17.62  17.48  17.58\n  E    00:42:28.8 -01:40:16  17.96     18.76  18.18  18.02",
  "circularId": 15650,
  "createdOn": 1388639358000,
  "email": "dperley@astro.caltech.edu",
  "subject": "GRB 131231A: P60 observations",
  "submitter": "Daniel Perley at Caltech  <dperley@astro.caltech.edu>",
  "eventId": "GRB 131231A"
}