{
  "bibcode": "2008GCN..8299....1G",
  "body": "C. Guidorzi, R. Margutti, J. Mao (INAF-OAB) and T. Sakamoto (GSFC/UMBC)\nreport on behalf of the Swift-XRT team:\n\nWe have analysed the first 7 orbits of Swift-XRT data obtained for\nGRB 080928 (Sakamoto et al., GCN Circ. 8292), covering 325 s of Windowed\nTiming (WT) mode data and 15.3 ks of Photon  Counting (PC) mode data.\nThe UVOT-enhanced XRT position was given by Osborne et al. in GCN Circ. \n8295.\n\nThe light-curve can be modelled by a broken power-law, with a couple\nof bright flares peaking at 210 and 360 s with a FWHM duration of 55\nand 35 s and a peak count rate of 420 +/- 10 and 75 +- 3 count s^-1,\nrespectively. The power-law decay index changes from an initial value\nof 1.20 +- 0.03 to 1.7 +- 0.2 after a break time of (11 +- 2) ks\n(uncertainties at 1 sigma). The first flare coincides with the main\nemission seen by BAT (Fenimore et al. GCN Circ. 8297).\n\nA spectrum extracted from WT data around the first flare, from 176 to 250 s,\ncan be modelled with an absorbed power-law, with Gamma = 1.45 +- 0.06 and\nNH = (1.7 +- 0.2)x1e21 cm^-2, in excess of the Galactic column in this\ndirection of 5.6e20 cm^-2. Another spectrum extracted around the second\nflare, from 300 to 470 s, can be fit with the same model, with\nGamma = 1.85 +- 0.06 and NH = (1.1 +- 0.2)x1e21 cm^-2.\nA later spectrum extracted from PC data, from 5 to 47 ks, can be fit with\nan absorbed power law with Gamma  = 2.2 +- 0.2 and NH = (1.2 +- 0.4)x1e21\ncm^-2. The observed (unabsorbed) flux over this time interval is 8.4x10^-12\n(1.2x10^-11) erg cm^-2 s^-1.\n\nIf the light-curve continues to decay with the current rate, the count\nrate 24 hours after the burst is estimated to be 5.6e-3 count s^-1, which\ncorresponds to an observed flux of 2.5x10^-13 erg cm^-2 s^-1.\n\nThis is an official product of the Swift-XRT team.",
  "circularId": 8299,
  "createdOn": 1222693001000,
  "email": "cristiano.guidorzi@brera.inaf.it",
  "subject": "GRB 080928: Swift-XRT refined analysis",
  "submitter": "Cristiano Guidorzi at INAF-OAB  <cristiano.guidorzi@brera.inaf.it>",
  "eventId": "GRB 080928"
}