{
  "subject": "GRB 250905A: Swift detection of a burst",
  "submitter": "David Palmer at LANL <palmer@lanl.gov>",
  "createdOn": 1757039134839,
  "submittedHow": "email",
  "eventId": "GRB 250905A",
  "circularId": 41714,
  "bibcode": "2025GCN.41714....1B",
  "body": "R. Brivio (INAF-OAB), S. Dichiara (PSU), D. M. Palmer (LANL),\nC. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB),\nB. Sbarufatti (INAF-OAB) and M. H. Siegel (PSU) report on behalf of\nthe Neil Gehrels Swift Observatory Team:\n\nAt 02:09:54 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 250905A (trigger=1347265).  Swift slewed immediately to the burst.\nThe BAT on-board calculated location is \nRA, Dec 233.047, +0.777 which is \n   RA(J2000) = 15h 32m 11s\n   Dec(J2000) = +00d 46' 39\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  Due to a telemetry gap, the BAT lightcurve\nis not immediately available.\n\nThe XRT began observing the field at 02:12:11.4 UT, 136.6 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source with an enhanced position: RA, Dec 233.00629, 0.79395\nwhich is equivalent to:\n   RA(J2000)  = 15h 32m 01.51s\n   Dec(J2000) = +00d 47' 38.2\"\nwith an uncertainty of 3.4 arcseconds (radius, 90% containment). This\nlocation is 158 arcseconds from the BAT onboard position, within the\nBAT error circle. This position may be improved as more data are\nreceived; the latest position is available at\nhttps://www.swift.ac.uk/sper.  We cannot determine whether the source\nis fading at the present time. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density consistent with the Galactic value of 5.50\nx 10^20 cm^-2 (Willingale et al. 2013).\n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 140 seconds after the BAT trigger. No credible afterglow candidate has\nbeen found in the initial data products. The 2.7'x2.7' sub-image covers none of\nthe XRT error circle. The 8'x8' region for the list of sources generated\non-board covers 100% of the XRT error circle. The list of sources is typically\ncomplete to about 18 mag. No correction has been made for the expected\nextinction corresponding to E(B-V) of 0.054.\n\nBurst Advocate for this burst is R. Brivio (riccardo.brivio AT inaf.it).\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"
}