{
  "eventId": "GRB 251002A",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "submittedHow": "email",
  "createdOn": 1759486009076,
  "bibcode": "2025GCN.42084....1K",
  "body": "J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester),\nJ.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini\n(INAF-OAB), E. Ambrosi\t(INAF-IASFPA), S. Lanava (PSU) and P.A. Evans\n(U. Leicester) reports on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of GRB 251002A. We\nsearched for X-ray sources in  1.5 ks of Photon Counting (PC) mode\ndata. The total exposure at the position of the afterglow (see below)\nis 1.5 ks, obtained between T0+3.6 ks and T0+9.2 ks.\n\nThree uncatalogued X-ray sources are detected within the estimated\n3-sigma SVOM/ECLAIRs error region (392 arcsec), of which one (\"Source\n1\") is above the RASS 3-sigma upper limit at this position, and is\ntherefore likely the GRB afterglow. Using 1503 s of PC mode data and 2\nUVOT images, we find an enhanced XRT position (using the XRT-UVOT\nalignment and matching UVOT field sources to the USNO-B1 catalogue):\nRA, Dec = 13.90813, -5.56678 which is equivalent to:\n\nRA (J2000): 00h 55m 37.95s\nDec(J2000): -05d 34' 00.4\"\n\nwith an uncertainty of 2.6 arcsec (radius, 90% confidence). This\nposition is consistent with the optical candidate (Palmerio et al. GCN\n42061) and the EP-FXT X-ray candidate (Sun et al. GCN 24075).\n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=1.27 (+0.28, -0.25).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.62 (+0.20, -0.18). The\nbest-fitting absorption column is  8.3 (+6.5, -2.8) x 10^20 cm^-2,\nconsistent with the Galactic value of 5.5 x 10^20 cm^-2 (Willingale et\nal. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux\nconversion factor deduced from this spectrum  is 4.2 x 10^-11 (4.7 x\n10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     8.3 (+6.5, -2.8) x 10^20 cm^-2\nGalactic foreground: 5.5 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.62 (+0.20, -0.18)\n\nIf the light curve continues to decay with a power-law decay index of\n1.27, the count rate at T+24 hours will be 0.014 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.9 x\n10^-13 (6.5 x 10^-13) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/03000125.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/SVOM/SVOM_FIELD00039.\n\nThis circular is an official product of the Swift-XRT team.\n\n",
  "subject": "GRB 251002A: Swift-XRT afterglow detection",
  "circularId": 42084
}