{
  "bibcode": "1999GCN...478....1T",
  "body": "T. Takeshima (USRA/GSFC), C. Markwardt (U.Md./GSFC),\nF. Marshall (GSFC), T.Giblin & R.M. Kippen (UAH/MSFC) report:\n\nRXTE has discovered an X-ray afterglow from the extremely bright\ngamma-ray burst detected with BATSE on 1999 Dec. 16.672 UT (Kippen et\nal., GCN Circ. 463, trigger number 7906).  Initial results from the\nRXTE observations have been distributed in two GCN Notices entitled\n\"GCN/RXTE_PCA BURST POSITION NOTICE\".  This circular summarizes the\nresults of the RXTE observations.\n\nThe first RXTE observation searched for an X-ray afterglow by scanning\nthe region around the BATSE LOCBURST position with the PCA, which has\n1-degree field-of-view.  In two of the scans a bright X-ray source was\ndetected, the first detection occurring at 1999 Dec. 16.840 UT or 4.02\nhours after the burst trigger, and second occurring about 200 seconds\nlater.  During both detections the pointing direction of the PCA was\nchanging most rapidly in R.A.  With such a scan pattern the source\nDeclination cannot be determined with as high a precision as the R.A.\nThe best-fit position from this observation was distributed through\nGCN at 22:49 UT on Dec. 16.\n\nRXTE scanned across the same source again at Dec. 17.126 UT or 10.90\nhours after the burst. During this observation the PCA scanned\nprimarily in the Declination direction.  The best-fit source position\nfor both observations is R.A. = 77.38 +/- 0.04 and Decl. = 11.30 +/-\n0.05 (J2000).  This position is consistent with the optical transient\ndetected by Uglesich et al (GCN 472).\n\nThe best-fit source intensities for the both observations were 1.24\n+/- 0.04 and 0.25 +/- 0.01, in units of 1e-10 erg/s/cm2 in the 2-10\nkeV band.  Assuming a power law decay, the evolution of the intensity\ncan be predicted (in the same units) by f = 0.065 x t**(-1.64) where t\nis the time in days after the burst trigger.\n\nPreliminary analysis of the source spectrum indicates a power-law\nshape with a photon index of about 2.1.\n\nThis message may be cited.",
  "circularId": 478,
  "createdOn": 945472941000,
  "email": "craigm@milkyway.gsfc.nasa.gov",
  "subject": "GRB 991216--Summary of RXTE Observations",
  "submitter": "Craig Markwardt at GSFC  <craigm@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 991216"
}