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GCN Circular 32171

Subject
GRB 220606A: Swift/BAT-GUANO detection
Date
2022-06-06T16:57:44Z (2 years ago)
From
Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com>
James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto),  Gayathri
Raman (PSU), Jamie A. Kennea (PSU), report:

Swift/BAT did not localize GRB 220606A onboard (T0: 2022-02-03T21:15:39.8
 UTC, Fermi/GBM GCN 32164).

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 9.8 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 5.7 and no specific location in the FOV
preferred.

Independent spectral and/or fluence measurements of this burst from
other instruments could help determine the preferred spatial origin.

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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