{
  "bibcode": "2009GCN..8797....1M",
  "body": "R. Margutti (Univ. Bicocca & INAF-OAB), J. Mao (INAF-OAB),\nT. Sakamoto (NASA/UMBC) report on behalf of the Swift XRT team:\n\nWe have analysed the first 2 orbits of Swift-XRT data obtained for\nGRB 090111 (Sakamoto et al., GCN Circ. 8795), covering 70 s of\nWindowed Timing (WT) and 4 ks of Photon Counting (PC) mode data,\nrespectively, between  77 s and 8 ks after the trigger.\nThe UVOT-enhanced XRT position was given by Evans et al. in\nGCN Circ. 8796.\n\nIn the time interval 77-150 s, the light curve can be modelled by a\nsimple power law with a decay index alpha_1= 5.1 +/- 0.3 (90% confidence)\nfollowed by a rebrightening around 0.5 ks.\nAfter the rebrightnening the light curve decays with a powerlaw index\nalpha_2= 3.6 +/- 0.4 and then flattens to alpha_3= 0.4 +/- 0.1\nwith a t_break of 1200 s.\n\nThe spectrum extracted from WT data can be modelled with an\nabsorbed simple power-law, with Gamma = 5.4 +/- 0.5  and\nNH = (5.4 +/- 0.8)x10^21 cm^-2 in excess of the Galactic column in\nthis direction which is 6.5x10^20 cm^-2 (Kalberla et al. 2005).\nThe observed (unabsorbed) 0.3 -10 keV\nflux over this time interval (77-150 s post-trigger) is\n3.8x10^-10 (2.7x10^-8) erg cm^-2 s^-1.\n\nThe spectrum extracted from PC data in the time interval 150-8000 s\ncan be modelled with an absorbed power-law, with Gamma= 3.3 +/- 0.5\nand an intrinsic column density of NH = (2.0 +/- 0.8)x10^21 cm^-2.\nThe observed (unabsorbed) 0.3 -10 keV flux over this time\ninterval is 3.0x10^-12 (1.2x10^-11) erg cm^-2 s^-1.\nUncertainties are given at 90% confidence.\n\nIf the light-curve continues to decay with alpha ~0.4, the count rate 24\nhours after the burst is estimated to be 1.3x10^-2 count s^-1, which\ncorresponds to an observed flux of 4x10^-13 erg cm^-2 s^-1.\n\nThe results of the xrt automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00339696.\n\nThis is an official product of the Swift-XRT team.",
  "circularId": 8797,
  "createdOn": 1231761947000,
  "email": "raffaella.margutti@brera.inaf.it",
  "subject": "GRB 090111: Swift-XRT refined analysis",
  "submitter": "Raffaella Margutti at U. di Milano Bicocca  <raffaella.margutti@brera.inaf.it>",
  "eventId": "GRB 090111"
}