{
  "circularId": 41379,
  "createdOn": 1755207097400,
  "subject": "GRB 250814A: Swift-XRT refined Analysis",
  "eventId": "GRB 250814A",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "body": "C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), S. Dichiara (PSU), J.A.\nKennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P.\nBeardmore (U. Leicester), R. Brivio (INAF-OAB) and P.A. Evans report on\nbehalf of the Swift-XRT team:\n\nWe have analysed 6.7 ks of XRT data for GRB 250814A, from 163 s to 40.1\nks after the   trigger. The data comprise 184 s in Windowed Timing (WT)\nmode (the first 10 s were taken while Swift was slewing) with the\nremainder in Photon Counting (PC) mode. The best available XRT position\n (using the promptly downlinked event data, the XRT-UVOT alignment and\nmatching UVOT field sources to the USNO-B1 catalogue) is RA, Dec =\n306.30792, 48.39903 which is equivalent to:\n\nRA (J2000): 20h 25m 13.90s\nDec(J2000): +48d 23' 56.5\"\n\nwith an uncertainty of 2.2 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with an initial power-law decay with an\nindex of alpha=1.49 (+0.27, -0.28), followed by a break at T+338 s to\nan alpha of 3.15 (+0.26, -0.20).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.33 (+0.24, -0.22). The\nbest-fitting absorption column is  1.2 (+0.4, -0.3) x 10^22 cm^-2, in\nexcess of the Galactic value of 6.5 x 10^21 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.9 (+/-0.4) and a\nbest-fitting absorption column of 1.0 (+0.4, -0.3) x 10^22 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 5.5 x 10^-11 (9.3 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.0 (+0.4, -0.3) x 10^22 cm^-2\nGalactic foreground: 6.5 x 10^21 cm^-2\nExcess significance: 1.8 sigma\nPhoton index:\t     1.9 (+/-0.4)\n\nIf the light curve continues to decay with a power-law decay index of\n3.15, the count rate at T+24 hours will be 1.3 x 10^-7 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.0 x\n10^-18 (1.2 x 10^-17) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01342439.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "bibcode": "2025GCN.41379....1S",
  "submittedHow": "email"
}