{
  "circularId": 38918,
  "eventId": "GRB 250106A",
  "body": "J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini\n(INAF-OAB), E. Ambrosi\t(INAF-IASFPA) , M. A. Williams (PSU), S.\nDichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P.\nBeardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on\nbehalf of the Swift-XRT team:\n\nSwift-XRT has conducted further observations of the field of the\nSVOM/ECLAIRs-detected burst GRB 250106A. The observations now extend\nfrom T0+20.2 ks to T0+579.8 ks and have a total exposure time of 7.9\nks.  \n\nOf the sources previously reported, \"Source 1\" is fading with >3-sigma\nsignificance, and is therefore likely the GRB afterglow. Using 2981 s\nof PC mode data and 3 UVOT images, we find an enhanced XRT position\n(using the XRT-UVOT alignment and matching UVOT field sources to the\nUSNO-B1 catalogue): RA, Dec = 117.23873, +63.81242 which is equivalent\nto:\n\nRA (J2000): 07h 48m 57.29s\nDec(J2000): +63d 48' 44.7\"\n\nwith an uncertainty of 3.0 arcsec (radius, 90% confidence). This\nposition is 3.4 arcmin from the SVOM/ECLAIRs position.\tThe source is\nfading with alpha >0.6.\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.4 (+0.8, -0.7). The\nbest-fitting absorption column is  3.7 (+3.4, -2.4) x 10^21 cm^-2, in\nexcess of the Galactic value of 4.5 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 3.1 x 10^-11 (6.2 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     3.7 (+3.4, -2.4) x 10^21 cm^-2\nGalactic foreground: 4.5 x 10^20 cm^-2\nExcess significance: 2.2 sigma\nPhoton index:\t     2.4 (+0.8, -0.7)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00021753.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/ToO_GRBs/00021753.\n\nThis circular is an official product of the Swift-XRT team.\n\n",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "createdOn": 1736763978050,
  "subject": "GRB 250106A: Swift-XRT afterglow detection",
  "submittedHow": "email",
  "bibcode": "2025GCN.38918....1O"
}