{
  "subject": "GRB 250108A: Swift-XRT afterglow detection",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "bibcode": "2025GCN.38853....1A",
  "eventId": "GRB 250108A",
  "createdOn": 1736353124711,
  "circularId": 38853,
  "submittedHow": "email",
  "body": "E. Ambrosi  (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), J.A. Kennea\n(PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P. Beardmore (U.\nLeicester), J.P. Osborne (U. Leicester), M. Perri (SSDC & INAF-OAR) and\nP.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nSVOM/ECLAIRs-detected burst GRB 250108A. We searched for X-ray sources\nin  2.7 ks of Photon Counting (PC) mode data. The total exposure at the\nposition of the afterglow (see below) is 3.2 ks, obtained between\nT0+16.1 ks and T0+34.4 ks.\n\nAn uncatalogued X-ray source is detected within the estimated 3-sigma\nSVOM/MXTs error region (98 arcsec) and is above the LSXPS 3-sigma upper\nlimit at this position, and is therefore likely the GRB afterglow.\nUsing 2670 s of PC mode data and 2 UVOT images, we find an enhanced XRT\nposition (using the XRT-UVOT alignment and matching UVOT field sources\nto the USNO-B1 catalogue): RA, Dec = 207.92093, +26.21642 which is\nequivalent to:\n\nRA (J2000): 13h 51m 41.02s\nDec(J2000): +26d 12' 59.1\"\n\nwith an uncertainty of 4.1 arcsec (radius, 90% confidence). This\nposition is 73 arcsec from the SVOM/MXTs position.  The source has a\nmean count rate of 1.7e-02 ct/sec; we cannot determine at the present\ntime whether it is fading.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00021755.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/ToO_GRBs/00021755.\n\nThis circular is an official product of the Swift-XRT team.\n\n"
}