{
  "submittedHow": "web",
  "subject": "GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew",
  "body": "Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC)  report:\n\nSwift/BAT did not localize GRB 250331D onboard (T0: 2025-03-31T05:49:17 UTC, Fermi GCN 39961).\n\nThe Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). \n\nUpon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.\n\nThe burst occurred during a Swift slew. The imaging is performed using BatAnalysis tools (Parsotan et al. 2025 [https://arxiv.org/abs/2502.00278](https://arxiv.org/abs/2502.00278)).\nA confident location is found for the burst with SNR of 11.6\n\nThe BAT position is\n\nRA, Dec = 48.52543, 62.30596 deg which is\n\n   RA(J2000)  = 03h 14m 06.10s\n   \n   Dec(J2000) =  +62d 18’ 21.5″\n   \nwith an estimated uncertainty of 5 arcmin.\n\nThis position is consistent with the Ferm/GBM localization (GCN 39961).\n\nXRT and UVOT follow-up has been requested. Results of follow-up\nobservations will be reported in future circulars.\n\nGUANO is a fully autonomous, extremely low latency, spacecraft\ncommanding pipeline designed for targeted recovery of BAT event mode\ndata around the times of compelling astrophysical events to enable\nmore sensitive GRB searches.\n\nA live reporting of Swift/BAT event data recovered by GUANO can be\nfound at: https://www.swift.psu.edu/guano/",
  "eventId": "GRB 250331D",
  "format": "text/markdown",
  "circularId": 39979,
  "bibcode": "2025GCN.39979....1R",
  "createdOn": 1743442564878,
  "submitter": "Samuele Ronchini at PSU <sjs8171@psu.edu>"
}