{
  "submittedHow": "web",
  "submitter": "Samuele Ronchini at PSU <sjs8171@psu.edu>",
  "subject": "GRB 231220A: Swift/BAT-GUANO arcminute localization of a long burst",
  "eventId": "GRB 231220A",
  "body": "Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC)  report:\n\nSwift/BAT did not localize GRB 231220A onboard (T0: 2023-12-20T16:10:17.4 UTC, Fermi/GBM GCN 35407).\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 BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), detects the burst in a 4.096 s analysis time bin with a sqrt(TS) of 28.32, starting at T0 - 1.02 s.\nAn arcminute localization is found with DeltaLLHOut of 48.29 and a DeltaLLHPeak of 49.13.\n\nSee Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.\n\nThe BAT position is\nRA, Dec = 27.321, 77.897 deg which is\n   RA(J2000)  = 01h 49m 17.04s\n   Dec(J2000) = +77d 53′ 49.2″\nwith an estimated uncertainty of 5 arcmin radius.\n\nXRT and UVOT follow-up has been requested.\nResults of follow-up observations 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/",
  "circularId": 35409,
  "createdOn": 1703110163183,
  "bibcode": "2023GCN.35409....1R"
}