{
  "bibcode": "2015GCN.17498....1P",
  "body": "C. Pagani (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), M.\nde Pasquale (INAF-IASFPA), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows\n(PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester) and M. G.\nBernardini (INAF-OAB) report on behalf of the Swift-XRT team:\n\nWe have analysed 6.7 ks of XRT data for GRB 150222A (Bernardini et al.\nGCN Circ. 17486), from 76 s to 44.7 ks after the  BAT trigger. The data\ncomprise 221 s in Windowed Timing (WT) mode (the first 10 s were taken\nwhile Swift was slewing) with the remainder in Photon Counting (PC)\nmode. The enhanced XRT position for this burst was given by Beardmore\net al. (GCN Circ. 17494).\n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=0.95 (+/-0.03). Some flaring activity is observed \nbetween T+250 s and T+650 s.\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.51 (+0.12, -0.11). The\nbest-fitting absorption column is  4.7 (+/-0.5) x 10^21 cm^-2, in\nexcess of the Galactic value of 3.3 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.45 (+0.19, -0.18)\nand a best-fitting absorption column of 5.8 (+1.0, -0.9) x 10^21 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.4 x 10^-11 (7.9 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     5.8 (+1.0, -0.9) x 10^21 cm^-2\nGalactic foreground: 3.3 x 10^20 cm^-2\nExcess significance: 10.0 sigma\nPhoton index:\t     2.45 (+0.19, -0.18)\n\nIf the light curve continues to decay with a power-law decay index of\n0.95, the count rate at T+24 hours will be 9.9 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.3 x\n10^-13 (7.8 x 10^-13) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00632180.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 17498,
  "createdOn": 1424690787000,
  "email": "grazia.bernardini@brera.inaf.it",
  "subject": "GRB 150222A: Swift-XRT refined Analysis",
  "submitter": "Maria Grazia Bernardini at INAF/Brera  <grazia.bernardini@brera.inaf.it>",
  "eventId": "GRB 150222A"
}