{
  "bibcode": "2015GCN.18272....1P",
  "body": "K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri\n(INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), D.N. Burrows\n(PSU), T.G.R. Roegiers (PSU), L.M. McCauley (PSU) and C. Pagani report\non behalf of the Swift-XRT team:\n\nWe have analysed 8.0 ks of XRT data for GRB 150910A (Pagani et al. GCN\nCirc. 18264), from 136 s to 35.1 ks after the  BAT trigger. The data\ncomprise 938 s in Windowed Timing (WT) mode (the first 7 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 Evans et\nal. (GCN Circ. 18271).\n\nThe late-time light curve (from T0+6.4 ks) can be modelled with a\nseries of power-law decays. The initial decay index is alpha=0.67\n(+0.23, -0.21). At T+10.9 ks  the decay steepens to an alpha of 3.17\n(+0.86, -0.30) before breaking again at T+20.3 ks to a final decay with\nindex alpha=1.3 (+/-0.4).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.56 (+/-0.04). The\nbest-fitting absorption column is  1.30 (+0.16, -0.15) x 10^21 cm^-2,\nin excess of the Galactic value of 5.4 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.77 (+0.09, -0.08)\nand a best-fitting absorption column of 7.1 (+2.3, -1.7) x 10^20 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.7 x 10^-11 (4.2 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     7.1 (+2.3, -1.7) x 10^20 cm^-2\nGalactic foreground: 5.4 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.77 (+0.09, -0.08)\n\nIf the light curve continues to decay with a power-law decay index of\n1.3, the count rate at T+24 hours will be 0.033 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x\n10^-12 (1.4 x 10^-12) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00655097.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 18272,
  "createdOn": 1441923963000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 150910A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 150910A"
}