{
  "body": "M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), J. J. DeLaunay (PSU),\nR. Gupta (NASA GSFC) and D. M. Palmer (LANL) report on behalf of the\nNeil Gehrels Swift Observatory Team:\n\nAt 00:55:56.71 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 250628A (trigger=1328546). Swift slewed immediately to the burst.\nThe BAT on-board calculated location is RA, Dec 38.551, -38.081 which is \n   RA(J2000) = 02h 34m 12s\n   Dec(J2000) = -38d 04' 50\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed two emission pulses with \nthe first brighter pulse starting from T0-20 sec to T0+20 sec and \nthe second fainter pulse from T0+25 end T0+60 sec.  The peak count rate\nwas ~1066 counts/sec (15-350 keV), at ~1 sec after the trigger.\n\nThe XRT began observing the field at 00:57:57.7 UT, 121.1 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nuncatalogued X-ray source with an enhanced position: RA, Dec 38.55240,\n-38.07909 which is equivalent to:\n   RA(J2000)  = 02h 34m 12.58s\n   Dec(J2000) = -38d 04' 44.7\"\nwith an uncertainty of 1.9 arcseconds (radius, 90% containment). This\nlocation is 7.9 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 in excess of the Galactic value (2.30 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.1\n(+4.01/-3.17) x 10^21 cm^-2 (90% confidence). \n\nThe initial flux in the 2.5 s image was 9.47e-10 erg cm^-2 s^-1 (0.2-10\nkeV).\n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 129 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 100% of\nthe XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag.\nThe 8'x8' region for the list of sources generated on-board covers 100% of the\nXRT error circle. The list of sources is typically complete to about 18 mag. No\ncorrection has been made for the expected extinction corresponding to E(B-V) of\n0.023.\n\nBurst Advocate for this burst is M. Ferro (matteo.ferro 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",
  "circularId": 40853,
  "eventId": "GRB 250628A",
  "submittedHow": "email",
  "submitter": "James DeLaunay at PSU <jjd330@psu.edu>",
  "bibcode": "2025GCN.40853....1F",
  "subject": "GRB 250628A: Swift detection of a burst",
  "createdOn": 1751073206767
}