{
  "subject": "GRB 250128B: Swift detection of a short burst",
  "circularId": 39058,
  "submittedHow": "email",
  "submitter": "P.A. Evans at U. Leicester <pae9@leicester.ac.uk>",
  "body": "P. A. Evans (U Leicester), R. A. J. Eyles-Ferris (U Leicester),\nR. Gupta (NASA GSFC), J. A. Kennea (PSU), K. L. Page (U Leicester),\nB. Sbarufatti (INAF-OAB) and M. A. Williams (PSU) report on behalf of\nthe Neil Gehrels Swift Observatory Team:\n\nAt 16:22:53 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 250128B (trigger=1285677).  Swift slewed immediately to the burst.\nThe BAT on-board calculated location is \nRA, Dec 231.420, -0.517 which is \n   RA(J2000) = 15h 25m 41s\n   Dec(J2000) = -00d 31' 01\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a single peak\nstructure with a duration of about 0.5 sec.  The peak count rate\nwas ~5578 counts/sec (15-350 keV), at ~0 sec after the trigger.\n\nThe XRT began observing the field at 16:24:12.3 UT, 78.6 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source with an enhanced position: RA, Dec 231.42552, -0.53970\nwhich is equivalent to:\n   RA(J2000)  = 15h 25m 42.12s\n   Dec(J2000) = -00d 32' 22.9\"\nwith an uncertainty of 1.9 arcseconds (radius, 90% containment). This\nlocation is 84 arcseconds from the BAT onboard position, within the BAT\nerror circle. This position may be improved as more data are received;\nthe latest position is available at https://www.swift.ac.uk/sper.  We\ncannot determine whether the source is 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 8.00\nx 10^20 cm^-2 (Willingale et al. 2013).\n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 82 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\n0.121.\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",
  "eventId": "GRB 250128B",
  "createdOn": 1738082313796,
  "bibcode": "2025GCN.39058....1E"
}