GCN Circular 35889

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

Swift/BAT did not localize GRB 240306A onboard (T0: 2024-03-06T06:45:49.58 UTC, Fermi/GBM trigger 731400355).

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 [-100,+100] 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 14 in a 2.048 s analysis time bin, starting at T0 + 0.512 s.

NITRATES results, independently, are ambiguous with respect to whether this burst originates from in or outside the BAT coded FOV, with a DeltaLLHOut of 1.86.

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://gcc02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.swift.psu.edu%2Fguano%2F&data=05%7C02%7Ccirculars%40gcn.nasa.gov%7C887a752fe810456574d308dc3dff6823%7C7005d45845be48ae8140d43da96dd17b%7C0%7C0%7C638453414370014126%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=9uFWgjFqiTq7UwRwDR3jCnnbjlNCgpcAfpIrKYtWGmc%3D&reserved=0