{
  "bibcode": "2014GCN.15673....1H",
  "body": "S. T. Holland (STScI) and\nV. Mangano (PSU)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began observations of the field of GRB 131231A 136.5 ks\nafter the Fermi/LAT trigger (Sonbas et al., 2013, GCNC 15640).  The\npreliminary UVOT position is\n\n     RA (J2000)  00:42:21.66  =  10.59025 (deg)\n    Dec (J2000) -01:39:10.6   =  -1.65294 (deg)\n\nwith an estimated uncertainty of 0.43 arcsec (radius, 90% confidence,\nstatistical + systematic).  We detect the optical afterglow at the\nposition reported by Xu et al. (2013, GCNC 15641).  Preliminary UVOT\nphotometry is presented below.\n\n------------------------------------------------------\nFilter      TSTART     TSTOP    Exposure     Mag   Err\n------------------------------------------------------\nu          246,875   248,554        1652   19.57  0.10\nwhite      136,762   138,942        1650   19.37  0.05\nwhite      228,985   231,172        1639   20.07  0.07\n------------------------------------------------------\n\nThe quoted magnitudes and upper limits have not been corrected for the\nGalactic extinction along the line of sight to this burst of E_{B-V} =\n0.02 mag (Schlafly et al. 2011, ApJS, 737, 103).  The photometry is in\nthe UVOT photometric system (Breeveld et al. 2011, AIP\nConf. Proc. 1358, 373).\n\nThe white observations yield a power-law decay index of alpha ~ 1.25\nbetween 1.6 and 2.7 days.  This is consistent with that found by\nPerley et al. (2014, GCNC 15650) between 1.0 and 1.9 days.  The\npower-law decay index in the X-ray band at this time is alpha ~ 1.6\n(Mangano et al. 2014, 15648), suggesting that there may be a cooling\nbreak between the optical and X-ray regimes.",
  "circularId": 15673,
  "createdOn": 1388778424000,
  "email": "sholland@stsci.edu",
  "subject": "GRB 131231A: Swift/UVOT Observations of the Optical Afterglow",
  "submitter": "Stephen Holland at STScI  <sholland@stsci.edu>",
  "eventId": "GRB 131231A"
}