{
  "bibcode": "2025GCN.41136....1O",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "circularId": 41136,
  "subject": "GRB 250721A: Swift-XRT observations",
  "submittedHow": "email",
  "eventId": "GRB 250721A",
  "body": "J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), T. Sbarrato\n(INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), D.N.\nBurrows (PSU), M.A. Williams (PSU), S. Dichiara (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 the MAXI-detected\nburst GRB 250721A in a series of observations tiled on the sky.  The\ntotal exposure time is\t1.4 ks, distributed over 5 tiles; the maximum\nexposure at a single sky location in the tiling was 569 s. The data\nwere collected between T0+16.2 ks and T0+22.9 ks, and are entirely in\nPhoton Counting (PC) mode. \n\nNo X-ray sources have been detected. The 3-sigma upper limit in the\nfield (not including the regions where the tiles overlap) ranges from\n~0.02 to ~0.05 ct s^-1, corresponding to a 0.3-10 keV observed flux of\n6.5e-13 to 2.2e-12 erg cm^-2 s^-1 (assuming a typical GRB spectrum).\n\nThe results of the XRT-team automatic analysis of the tiled XRT\nobservations, including a position-specific upper limit calculator, are\navailable at https://www.swift.ac.uk/xrt_products/TILED_GRB00137.\n\nThis circular is an official product of the Swift-XRT team.\n\n",
  "createdOn": 1753191967600
}