{
  "body": "Samuele Ronchini (PSU), Gayathri Raman (PSU), James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:\n\nSwift/BAT did not localize GRB 230518A onboard (T0: 2023-05-18T22:49:27.61 UTC, Fermi/GBM GCN 33822). \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 with a sqrt(TS) of 11 in a 0.128 s analysis time bin.\nThe burst duration is ~0.256 seconds.\n\nNITRATES results, independently, are ambiguous with respect to whether this burst originates from in or outside the BAT coded FOV, with a borderline DeltaLLHOut of 6.5.\nThe majority of the Fermi/GBM localization lies outside the coded FOV.\n\nSee Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.\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 230518A",
  "submitter": "Aaron Tohuvavohu at University of Toronto <aaron.tohu@gmail.com>",
  "circularId": 33825,
  "bibcode": "2023GCN.33825....1R",
  "createdOn": 1684496093617,
  "subject": "GRB 230518A: Swift/BAT-GUANO detection"
}