{
  "bibcode": "2018GCN.22685....1D",
  "body": "V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), S. J. LaPorte (PSU), J.A.\nKennea (PSU), B. Sbarufatti (INAF-OAB/PSU), K.L. Page (U. Leicester),\nA.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), A. Melandri\n(INAF-OAB) and A.Y. Lien report on behalf of the Swift-XRT team:\n\nWe have analysed 12 ks of XRT data for GRB 180504A (Lien et al. GCN\nCirc. 22682), from 98 s to 30.5 ks after the  BAT trigger. The data\ncomprise 163 s in Windowed Timing (WT) mode (the first 8 s were taken\nwhile Swift was slewing) with the remainder in Photon Counting (PC)\nmode. The best available XRT position  (using the promptly downlinked\nevent data, the XRT-UVOT alignment and matching UVOT field sources to\nthe USNO-B1 catalogue) is RA, Dec = 331.1442, -14.6583 which is\nequivalent to:\n\nRA (J2000): 22 04 34.61\nDec(J2000): -14 39 30.0\n\nwith an uncertainty of 2.0 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=0.7 (+nan, -nan).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.80 (+/-0.11). The\nbest-fitting absorption column is  6.9 (+3.2, -2.8) x 10^20 cm^-2, in\nexcess of the Galactic value of 3.5 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.86 (+0.25, -0.23)\nand a best-fitting absorption column of 1.5 (+0.8, -0.7) x 10^21 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.7 x 10^-11 (4.6 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.5 (+0.8, -0.7) x 10^21 cm^-2\nGalactic foreground: 3.5 x 10^20 cm^-2\nExcess significance: 2.7 sigma\nPhoton index:\t     1.86 (+0.25, -0.23)\n\nIf the light curve continues to decay with a power-law decay index of\n0.7, the count rate at T+24 hours will be 7.4 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.8 x\n10^-13 (3.4 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/00830822.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 22685,
  "createdOn": 1525507782000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180504A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180504A"
}