{
  "createdOn": 1756421775440,
  "submitter": "David Palmer at LANL <palmer@lanl.gov>",
  "bibcode": "2025GCN.41581....1E",
  "circularId": 41581,
  "body": "P. A. Evans (U Leicester), R. Gupta (NASA GSFC), J. A. Kennea (PSU),\nK. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)\nreport on behalf of the Neil Gehrels Swift Observatory Team:\n\nAt 22:33:37 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 250828B (trigger=1345836).  Swift could not slew to the\nburst due to an observing constraint.\nThe BAT on-board calculated location is \nRA, Dec 124.852, -17.388 which is \n   RA(J2000) = 08h 19m 24s\n   Dec(J2000) = -17d 23' 17\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a single-peaked\nstructure with a duration of about 8 sec.  The peak count rate\nwas ~1700 counts/sec (15-350 keV), at ~0 sec after the trigger.\n\nDue to a Sun observing constraint, Swift cannot slew to the BAT\nposition until 17:55 UT on 2025 September 07. There will thus be no XRT\nor UVOT data for this trigger before this time.\n\nWe note that this GRB is coincident within one minute with a \nsubthreshold Gravitational Wave trigger S250828ef, at \n22:32:44 UT. However, this GW trigger is of low confidence, rated\nas 99% likely to be Terrestrial background noise.\n\nBurst Advocate for this burst is P. A. Evans (pae9 AT leicester.ac.uk).\nPlease contact the BA by email if you require additional information\nregarding Swift followup of this burst. In extremely urgent cases, after\ntrying the Burst Advocate, you can contact the Swift PI by phone (see\nSwift TOO web site for information: http://www.swift.psu.edu/)\n\n",
  "subject": "GRB 250828B: Swift detection of a burst",
  "submittedHow": "email",
  "eventId": "GRB 250828B"
}