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GCN Circular 32824

Subject
GRB 221022A: Swift/BAT-GUANO detection
Date
2022-10-24T02:41:40Z (2 years ago)
From
Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com>
Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), James DeLaunay
(UAlabama), Jamie A. Kennea (PSU), Tyler Parsotan (GSFC/UMBC) report:

Swift/BAT did not localize GRB 221022A onboard (T0: 2022-10-22T19:33:33
 UTC, Fermi/GBM GCN 32816).

The 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).

Upon trigger, 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.

The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu,
arXiv:2111.01769), detects the burst with a sqrt(TS) of 8.7 in a 4.096
s analysis time bin.

NITRATES results, independently, are ambiguous with respect to whether
this burst originates from in or outside the BAT FOV, with a
borderline DeltaLLHOut of 9.5.

The best fit In FOV position is very weakly preferred over other
positions, with DeltaLLHPeak of 2.1. This position is consistent with
the Fermi/GBM localization (GCN 32816).

The candidate position is
RA, Dec = 118.342, -5.117 which is
   RA(J2000)  = 07h 53m 22.03s
   Dec(J2000) = -5d 07��� 00.9���
with an estimated uncertainty of 5 arcmin.

See Section 9.1 and Figure 20 in the NITRATES paper for brief
descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and
DeltaLLHOut.

GUANO 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.

A live reporting of Swift/BAT event data recovered by GUANO can be
found at: https://www.swift.psu.edu/guano/
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