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GCN Circular 35065

Subject
GRB 231115A: Swift/BAT-GUANO detection of a short burst
Date
2023-11-16T17:46:12Z (4 months ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form
Samuele Ronchini (PSU), Aaron Tohuvavohu (U Toronto), James DeLaunay (PSU), Gayathri Raman (PSU), Tyler Parsotan (NASA GSFC), Jamie A. Kennea (PSU) report: 

Swift/BAT did not localize GRB 231115A onboard (T0: 2023-11-15T15:36:21.2 UTC, Fermi GCN 35035, Integral GCN 35037, Glowbug GCN 35045, Insight-HXMT/HE GCN 35060, Konus-Wind GCN 35062).

The Fermi and Integral notices, 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 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. 

The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 20.26 in a 0.128 s analysis time bin, starting at T0.

NNITRATES results, independently, are ambiguous with respect to whether this burst originates from in or outside the BAT coded FOV, with a DeltaLLHOut of 8.9.
The Integral localization, coincident with M82, is consistent with being outside the BAT coded FOV.

The very short duration and the large E_peak (best fit value from the spectral template of 720 keV) are consistent with the Magnetar Giant Flare scenario (GCN 35044, GCN 35059).

See Section 9.1 and Figures 10 and 17 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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