{
  "subject": "GRB 250916A: Swift-XRT observations",
  "body": "J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), C. Salvaggio\n(INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows\n(PSU), S. Lanava (PSU), S. Dichiara (PSU) and P.A. Evans (U. Leicester)\nreports on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nFermi/GBM-detected burst GRB 250916A, collecting  1.6 ks of Photon\nCounting (PC) mode data between T0+101.9 ks and T0+107.2 ks. \n\nOne uncatalogued X-ray source has been detected within the estimated\n3-sigma GOTO error region (0.8 arcsec) given in GCN Circ. 41847, it is\nbelow the RASS limit and shows no definitive signs of fading. However,\ngiven its coincident location with the fading optical source, it is\nindeed likely to be the afterglow. Details of this source are given\nbelow:\n\nSource 1:\n  RA (J2000.0):  26.5708  =  01h 46m 16.99s\n  Dec (J2000.0): +36.1652  =  +36d 09' 54.6\"\n  Error: 3.7 arcsec (radius, 90% conf. [Enhanced position])\n  Count-rate: 0.0274 +/- 0.0049 ct s^-1   \n  Distance: 2 arcsec from GOTO position.\n  Flux: (9.2 +/- 1.6)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)\n\nAn uncatalogued source was also detected, however this was too far from\nthe GRB position to be the afterglow.\n\nThe results of the XRT-team automatic analysis of the XRT observations,\nincluding a position-specific upper limit calculator, are available at\nhttps://www.swift.ac.uk/ToO_GRBs/00021859.\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>",
  "bibcode": "2025GCN.41862....1O",
  "createdOn": 1758182309497,
  "eventId": "GRB 250916A",
  "circularId": 41862,
  "submittedHow": "email"
}