{
  "circularId": 33653,
  "createdOn": 1681887724652,
  "bibcode": "2023GCN.33653....1R",
  "submitter": "Aaron Tohuvavohu at University of Toronto <aaron.tohu@gmail.com>",
  "eventId": "GRB 230418A",
  "body": "Samuele Ronchini (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto), Tyler Parsotan (UMBC/GSFC) report: \n\nSwift/BAT did not localize GRB 230418A onboard (T0: 2023-04-18T21:11:33.49 UTC, Fermi/GBM GCN 33652) \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 31.1 in a 0.256 s analysis time bin. \nThe burst duration as seen by BAT is ~0.25 seconds.\n\nNITRATES results indicate a burst coming from outside the FOV, with DeltaLLHOut of -20.\nThe NITRATES best fit OFOV position is consistent with the Fermi/GBM localization (GCN 33652).\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 commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. \n\nA live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/\n",
  "subject": "GRB 230418A: Swift/BAT-GUANO detection outside the coded FOV"
}