{
  "bibcode": "2025GCN.39681....1K",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "circularId": 39681,
  "body": "J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P.\nBeardmore (U. Leicester), J.P. Osborne (U. Leicester), R. Brivio\n(INAF-OAB), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR) and P.A.\nEvans (U. Leicester) reports on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the MAXI-detected\nburst GRB 250311A/MAXI J1457-026 (GCN Circ. 39660) in a series of\nobservations tiled on the sky.\tThe total exposure time is  1.4 ks,\ndistributed over 4 tiles; the maximum exposure at a single sky location\nin the tiling was 731 s. The data were collected between T0+34.4 ks and\nT0+36.0 ks, and are entirely in Photon Counting (PC) mode. \n\nTwo uncatalogued X-ray sources have been detected, however none of them\nis above the RASS limit or shows definitive signs of fading. Therefore,\nat the present time we cannot identify which, if any, is the afterglow.\nDetails of these sources are given below:\n\nSource 1:\n  RA (J2000.0):  224.4476  =  14:57:47.43\n  Dec (J2000.0): -2.7859  =  -02:47:09.2\n  Error: 9.8 arcsec (radius, 90% conf.)\n  Count-rate: (9.8 [+6.3, -4.5])e-3 ct s^-1   \n  Distance: 777 arcsec from MAXI position.\n\nSource 2:\n  RA (J2000.0):  224.4381  =  14:57:45.15\n  Dec (J2000.0): -2.7813  =  -02:46:52.7\n  Error: 8.7 arcsec (radius, 90% conf.)\n  Count-rate: 0.0134 [+0.0074, -0.0055] ct s^-1   \n  Distance: 744 arcsec from MAXI position.\n\nWe note that these observations do not cover the localisation of X-ray\ntransient EP250311a (GCN 39664), which may be associated with the same\ntrigger.\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_GRB00135.\n\nThis circular is an official product of the Swift-XRT team.\n\n",
  "subject": "GRB 250311A: Swift-XRT observations",
  "submittedHow": "email",
  "createdOn": 1741773480859,
  "eventId": "GRB 250311A"
}