{
  "bibcode": "2005GCN..2955....1H",
  "body": "J. E. Hill, J. A. Kennea, D. C. Morris, D. N. Burrows (PSU), A. A. Wells, J. P.\nOsborne (U. Leicester), G. Tagliaferri (OAB), M. Ivanushkina, S. Hunsberger, J.\nA. Nousek, P. Roming (PSU), P. Schady (MSSL), S. Barthelmy, F. Marshall and N.\nGehrels (NASA/GSFC) report on behalf of the Swift XRT team:\n\nWe have derived a refined Swift XRT position for GRB050117, based on preliminary\nalignment corrections to the raw position reported in Burrows et al. (GCN 2951).\n\nThe refined XRT position is:\nRA(J2000) = 358.47067 = 23h 53m 53.0s\nDec(J2000) = +65.93882 = +65:56:20\n\nThe estimated uncertainty in this position is 15 arcseconds (radius).\n\nThis is the first time that the Swift observatory has executed a prompt slew to\na GRB, and the XRT position was measured 192 seconds after the burst occurred.\nBecause the burst was quite long, the first XRT data were collected before the\nburst ended, a first for a focussed X-ray GRB/afterglow observation.  We note\nthat the XRT in-flight calibration program has not yet begun because the Swift\nobservatory is still in its commissioning phase.\n\nThe burst occurred at 12:52:36 UT (Sakamoto et al., GCN 2952) just before Swift\nentered the South Atlantic Anomaly (SAA) and while the burst location was\nwithin the Swift Earth limb constraint.  The Swift spacecraft began slewing to\nthe burst at 12:54:38 UT, while in the SAA.  The XRT imaged the source\nimmediately after the slew ended, at 12:55:48.64 UT.  The source was very\nbright, resulting in a successful centroid on the first 0.1s Image Mode\nexposure. The XRT then collected a partial Photodiode Mode frame and stopped\ndata collection because it was in the SAA.  Although we have not yet calibrated\nfluxes measured in XRT's Image Mode, the X-ray source intensity in the Image\nMode frame appears to be comparable to Cyg X-2, which puts it at roughly 1/2\nCrab (based on RXTE ASM data on Cyg X-2 and the Crab).\n\nThe source is located just outside the zero-visibility region around the Swift\norbit pole and has only short periods of visibility on each orbit.  Most of\nthese visible periods occur while Swift is in the SAA, which limits the\namount of time when the source can be viewed by the XRT.  Automated observations\nwill proceed for the rest of 2005 Jan 17 when the source is visible.  We expect\nto obtain a total observing time of about 15 minutes, spread out between 12:55\nUT and 19:29 UT.  Because of orbital precession, the source will not be visible\nagain by the Swift XRT until 2005 Jan 21.",
  "circularId": 2955,
  "createdOn": 1105985363000,
  "email": "burrows@astro.psu.edu",
  "subject": "GRB050117: Refined XRT position",
  "submitter": "David Burrows at PSU/Swift  <burrows@astro.psu.edu>",
  "eventId": "GRB 050117"
}