{
  "bibcode": "2018GCN.22632....1G",
  "body": "S.L. Gibson (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri\n(INAF-OAB), P. D'Avanzo (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), D.N.\nBurrows (PSU), A. Tohuvavohu (PSU), J.P. Osborne (U. Leicester) and Z.\nLiu report on behalf of the Swift-XRT team:\n\nWe have analysed 9.3 ks of XRT data for GRB 180411A (Liu et al. GCN\nCirc. 22630), from 72 s to 29.8 ks after the  BAT trigger. The data\ncomprise 200 s in Windowed Timing (WT) mode with the remainder in\nPhoton Counting (PC) mode. The refined XRT position is RA, Dec =\n356.8540, +66.7785 which is equivalent to:\n\nRA (J2000): 23 47 24.97\nDec(J2000): +66 46 42.5\n\nwith an uncertainty of 3.5 arcsec (radius, 90% confidence).\n\nThe late-time light curve (from T0+4.4 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.09 (+/-0.07).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.68 (+/-0.10). The\nbest-fitting absorption column is  1.54 (+0.16, -0.15) x 10^22 cm^-2,\nin excess of the Galactic value of 8.3 x 10^21 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.01 (+/-0.16) and a\nbest-fitting absorption column of 1.91 (+0.25, -0.23) x 10^22 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 5.9 x 10^-11 (1.3 x 10^-10) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.91 (+0.25, -0.23) x 10^22 cm^-2\nGalactic foreground: 8.3 x 10^21 cm^-2\nExcess significance: 7.7 sigma\nPhoton index:\t     2.01 (+/-0.16)\n\nIf the light curve continues to decay with a power-law decay index of\n1.09, the count rate at T+24 hours will be 0.032 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x\n10^-12 (4.1 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/00824451.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 22632,
  "createdOn": 1523487102000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180411A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180411A"
}