GCN Circular 35022

Aaron Tohuvavohu (U Toronto), James DeLaunay (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Samuele Ronchini (PSU)  report:

Swift/BAT did not localize SGRJ1555-5402 onboard (T0: 2023-11-11T21:35:11.4 UTC, Fermi trigger n. 721431316).

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 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), detects the burst in a 0.128 s analysis time bin with a sqrt(TS) of 29.2, starting at T0 - 0.128 s. 
An arcminute localization is found with DeltaLLHOut of 86.12 and a DeltaLLHPeak of 112.11.

From the spectral template, the best fit value of the peak energy is 77.6 keV.

See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.

The BAT position is
RA, Dec = 238.818, -54.077 deg which is
   RA(J2000)  =  15h 55m 16.32s
   Dec(J2000) = -54d 04m 37.20s
with an estimated uncertainty of 5 arcmin radius.

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/