{
  "bibcode": "2017GCN.22219....1S",
  "body": "B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), S.L. Gibson (U.\nLeicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), P.\nD'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A.\nTohuvavohu (PSU) and S.J. LaPorte report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 6.3 ks of XRT data for GRB 171209A (LaPorte et al. GCN\nCirc. 22213), from 92 s to 17.9 ks after the  BAT trigger. The data\ncomprise 349 s in Windowed Timing (WT) mode (the first 5 s were taken\nwhile Swift was slewing) with the remainder in Photon Counting (PC)\nmode. Using 2454 s of PC mode data and 6 UVOT images, we find an\nenhanced XRT position (using the XRT-UVOT alignment and matching UVOT\nfield sources to the USNO-B1 catalogue): RA, Dec = 139.40280, -30.52016\nwhich is equivalent to:\n\nRA (J2000): 09h 17m 36.67s\nDec(J2000): -30d 31' 12.6\"\n\nwith an uncertainty of 1.7 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with a series of power-law decays. The\ninitial decay index is alpha=1.87 (+/-0.08). At T+231 s  the decay\nsteepens to an alpha of 3.42 (+0.26, -0.22) before breaking again at\nT+629 s to a final decay with index alpha=0.74 (+0.12, -0.11).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.37 (+/-0.04). The\nbest-fitting absorption column is  2.54 (+0.27, -0.25) x 10^21 cm^-2,\nin excess of the Galactic value of 2.1 x 10^21 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.06 (+0.08, -0.07)\nand a best-fitting absorption column consistent with the Galactic\nvalue. The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 3.4 x 10^-11 (4.5 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     2.11 (+0.10, -0.00) x 10^21 cm^-2\nGalactic foreground: 2.1 x 10^21 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     2.06 (+0.08, -0.07)\n\nIf the light curve continues to decay with a power-law decay index of\n0.74, the count rate at T+24 hours will be 0.036 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x\n10^-12 (1.6 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/00796100.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 22219,
  "createdOn": 1512858341000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 171209A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 171209A"
}