{
  "bibcode": "2009GCN..9876....1S",
  "body": "G. Stratta, V. D'Elia, M. Perri (ASDC) report on behalf of the\nSwift XRT team:\n\nAt 23:36 UT, September 2nd, 2009, Swift began a Target of Opportunity\nobservation of the Fermi GBM/LAT discovered burst GRB 090902B (de\nPalma et al., GCN 9867, Bissaldi et al., GCN 9866) about 12.5 hours\nafter the trigger.\n\nWe confirm that the X-ray source reported by Kennea et al. (GCN\nCirc. 9868) shows a decaying behavior and is likely the afterglow of\nGRB 090902B.\n\nThe enhanced XRT position for this burst was given by Evans\n(GCN. Circ 9871).\n\nThe X-ray light curve from T+12.53 hr to T+17.38 hr can be fit with\na single power-law model with a decay index of -1.3+/-0.9 (90% confidence\nlevel).\n\nWith 4.8 ks of integration time, the X-ray spectrum from T+12.53 hr to T+17.38 hr\nafter the Fermi/GBM trigger can be fit by an absorbed power-law model\nwith a photon index of 2.1 (+0.3,-0.3) and a rest frame column density of\n(3.4+/-0.9) x 10^22 cm^-2 at z=1.822 (Cucchiara et al., GCN 9873)\nin addition to the Galactic column density\nin the direction of the burst (3.88 x 10^20 cm^-2, Kalberla et al. 2005).\nErrors are at 90% confidence level.\nThe observed 0.3-10.0 keV flux is 3.2 x 10^-12 erg cm^-2 s^-1 which\ncorresponds to an unabsorbed flux of 4.1 x 10^-12  erg cm^-2 s^-1.\n\nProviding the source continues to decay at the same rate, we predict an\nobserved flux of about 8.7 x 10^-13 erg cm^-2 s^-1 at T+2 days.\n\nThis circular is an official product of the Swift-XRT team.\n\n[GCN OPS NOTE(03sep09): Per author's request, the missing Cucchiara\nreference was added.]",
  "circularId": 9876,
  "createdOn": 1251991829000,
  "email": "stratta@asdc.asi.it",
  "subject": "GRB090902B: Swift XRT refined analysis",
  "submitter": "Giulia Stratta at ASDC  <stratta@asdc.asi.it>",
  "eventId": "GRB 090902B"
}