{
  "createdOn": 1742204886867,
  "circularId": 39758,
  "bibcode": "2025GCN.39758....1B",
  "body": "A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini\n(INAF-OAB), E. Ambrosi\t(INAF-IASFPA) , J.A. Kennea (PSU), D.N. Burrows\n(PSU), M. A. Williams (PSU), J.P. Osborne (U. Leicester) and P.A. Evans\n(U. Leicester) reports on behalf of the Swift-XRT team:\n\nSwift-XRT has conducted further observations of the field of the\nSwift/BAT-detected burst GRB 250316A. The observations now extend from\nT0+21.7 ks to T0+51.0 ks and have a total exposure time of 4.6 ks. .\nThe source previously reported, \"Source 1\", is believed to be the\nafterglow. Using 3006 s of PC mode data and 2 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 = 219.59644, +14.89108\nwhich is equivalent to:\n\nRA (J2000): 14h 38m 23.15s\nDec(J2000): +14d 53' 27.9\"\n\nwith an uncertainty of 3.0 arcsec (radius, 90% confidence). This\nposition is 118 arcsec from the Swift/BAT position.  The source is\nfading with alpha >0.9.\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.7 (+0.9, -0.7). The\nbest-fitting absorption column is  5.1 (+4.0, -2.8) x 10^21 cm^-2, in\nexcess of the Galactic value of 1.5 x 10^20 cm^-2 (Willingale et al.\n2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 3.0 x 10^-11 (8.4 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     5.1 (+4.0, -2.8) x 10^21 cm^-2\nGalactic foreground: 1.5 x 10^20 cm^-2\nExcess significance: 2.9 sigma\nPhoton index:\t     2.7 (+0.9, -0.7)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00021823.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/ToO_GRBs/00021823.\n\nThis circular is an official product of the Swift-XRT team.\n\n",
  "submittedHow": "email",
  "eventId": "GRB 250316A",
  "subject": "GRB 250316A: Swift-XRT afterglow detection",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>"
}