{
  "subject": "GRB020331: Late-time Optical Light Curve",
  "eventId": "GRB 020331",
  "bibcode": "2002GCN..1459....1S",
  "createdOn": 1027527314000,
  "circularId": 1459,
  "submitter": "Alicia Soderberg at Caltech  <ams@astro.caltech.edu>",
  "email": "ams@astro.caltech.edu",
  "body": "A. M. Soderberg, D. W. Fox, and S. R. Kulkarni (Caltech) report\non behalf of the larger Caltech-NRAO-CARA GRB collaboration.\n\n\"We have observed the optical afterglow associated with GRB 020331\n(GCN 1334) with HST+STIS (Clear) at four epochs spanning the period\n25-50 days following the burst (one orbit per epoch).\n\nRegistration of the STIS data against ground-based images allows us to\nidentify the afterglow amidst a complex of at least three galaxies,\nincluding the presumed host galaxy which lies under the afterglow\nitself.  Aperture photometry on the optical transient + host yields\nthe following R-equivalent magnitudes for the first three epochs:\n\n    HST Epoch   T (days since burst)     R (mag)\n       1        23.9                     24.54 +/- 0.07\n       2        36.6                     25.01 +/- 0.10\n       3        42.7                     24.76 +/- 0.09\n\nWe have derived our R-equivalent magnitudes by assuming\n(R-Clear)=-0.67 as given by the STIS Exposure Time Calculator for\na source with power-law spectrum (index=-1).\nThese values imply a power-law flux decay index over this interval with\nindex alpha=0.75, compatible with previous ground-based estimates\n(Ricker et al., GCN 1382).\n\nPreliminary analysis of the fourth epoch, T=50 days, indicates a\nrebrightening of the optical afterglow by 0.2 +/- 0.1 mag as compared\nwith our Epoch 3.  We have requested additional HST observations to\nhelp us clarify whether this rebrightening is statistically significant.\n\nA finding chart of the field can be found at:\n\n\thttp://www.astro.caltech.edu/~ams/grb020331.html\n\nThis message may be cited.\""
}