{
  "bibcode": "1999GCN...477....1D",
  "body": "GRB 991216 Optical Observations\n\nA. Diercks (Caltech), L. Ferrarese (UCLA), J. S. Bloom (Caltech) report\non behalf of the Caltech-NRAO-CARA GRB collaboration:\n\n\"We imaged the field of GRB 991216 in Gunn-i on UT Dec. 17.214 and\nDec. 17.462 UT using the Palomar 200-inch with the COSMIC imager under\nphotometric conditions.  At each epoch we took three exposures of 300s\neach centered on the RXTE-PCA error circle (Takeshima et al. 1999).\nThe OT identified by Halpern (GCN #472) is well detected in each image\nand faded 0.48 +/- 0.04 mag between epochs.  This corresponds to a\npower-law decay index of alpha = -1.2 +/- 0.1.\n\nBased on observations of Landolt standards in SA 94 and conversion to\nGunn-i magnitudes (Wade et al., PASP 91:35), we estimate the\nbrightness at i = 19.1 +/- 0.2 on Dec. 17.214 UT and i = 19.6 +/- 0.2\non Dec. 17.463 UT.  Refinement of these absolute magnitudes will be\npossible as soon as better absolute calibrations are available.  We\nnote that the dust maps of Schlegal,Finkbinder, and Davis (ApJ, 500,\n525) give E(B-V) = 0.634 at this position, (l,b) = (190.44,-16.63),\ncorresponding to A(Gunn-i) = 1.3 for extra-galactic sources.\"\n\nThis message may be cited.",
  "circularId": 477,
  "createdOn": 945469851000,
  "email": "ad@astro.caltech.edu",
  "subject": "GRB 991216 Optical Observations",
  "submitter": "Alan H. Diercks at Caltech  <ad@astro.caltech.edu>",
  "eventId": "GRB 991216"
}