{
  "subject": "GRB071118: Swift XRT refined analysis",
  "eventId": "GRB 071118",
  "bibcode": "2007GCN..7111....1M",
  "createdOn": 1195466343000,
  "circularId": 7111,
  "submitter": "Alberto Moretti at Obs Brera Merate  <alberto.moretti@brera.inaf.it>",
  "email": "alberto.moretti@brera.inaf.it",
  "body": "A. Moretti (INAF-OAB), J. R. Cummings (NASA/UMBC), C. Guidorzi\n(Univ. Bicocca & INAF-OAB), P. Romano (Univ. Bicocca & INAF-OAB),\nP. Evans (U Leicester)report on behalf of the Swift-XRT team:\n\nWe have analysed the first 4 orbits of Swift-XRT data obtained for GRB\n071118 (trigger number 296856, Cummings et al., GCN Circ. 7106).  The\ndata consist of 122 s in Windowed Timing (WT) mode, starting 128\ns after the BAT trigger and 8.8 ks in Photon Counting (PC) mode.\nUsing 1298 s of overlapping XRT Photon Counting mode and UVOT V-band\ndata, we find an astrometrically corrected X-ray position (using the\nXRT-UVOT alignment and matching UVOT field sources to the USNO-B1\ncatalogue): RA, Dec = 299.71558, 70.12449 which is equivalent to:\n\nRA (J2000):  19 58 51.74\nDec (J2000): +70 07 28.2\n\nwith an uncertainty of 1.6 arcsec (radius, 90% confidence).  This\nlocation is 2.7 arcseconds from the XRT position measured using prompt\ndownlinked data (Cummings et al., GCN Circ. 7106) and 152 arcseconds\nfrom the BAT refined position (Markwardt et al.  GCN Circ. 7109).\n\nThe light-curve, in the first orbit (up to 2 ks from the trigger)\nshows a steep decay accompanied by flaring activity Since the second\norbit, the afterglow shows a more regular decay with a shallow phase\n(alpha1=0.6+/-0.2) until 11 ks and a steeper decay (alpha2=1.6+/-0.2).\n\nThe spectrum formed from all the WT data can be modelled with a\npower-law of photon index Gamma = 1.64 +/- 0.13, with an absorbing\ncolumn of NH = (2.7 +/- 0.6)e21 cm^-2 (in excess with respect to the\nGalactic value of 9.7e20 cm^-2). The spectrum formed from the PC data\ncan be modelled with a power-law of photon index Gamma = 1.62 +/-\n0.06, with an absorbing column of NH = (2.6 +/- 0.4)e21 cm^-2, which\nis consistent with the previous one.\n\nAssuming the light-curve continues to decay with alpha2=1.6, the count\nrate at 48 hours is predicted to be 0.002 count s^-1. This corresponds\nto an observed (unabsorbed) flux of 1.3e-13 (1.7e-13) erg cm^-2 s^-1.\n\nThis circular is an official product of the Swift-XRT team."
}