GRB 231214B

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

Swift/BAT did not localize GRB 231214B onboard (T0: 2023-12-14T07:53:55.52 UTC, Fermi GBM Trig 724233240). 

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), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 8.6 in a 16.384 s analysis time bin, starting at T0 - 8.192 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 8.2.

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/

E. Bissaldi (Politecnico and INFN Bari) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:


"At 07:53:55.52 UT on 14 December 2023, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 231214B (trigger 724233240 / 231214329),
which was also detected by the Swift/BAT-GUANO (DeLaunay et al. 2023, GCN 35340
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 ).

The on-ground calculated location, using the GBM trigger
data, is RA = 137.9, DEC = -13.4 (J2000 degrees,
equivalent to 09h 11m 36, -13d 24'), with a statistical uncertainty
of 6.3 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90% of
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).

The angle from the Fermi LAT boresight at the GBM trigger time is 78 degrees.

The GBM light curve shows a single weak and structured emission episode
with a duration (T90) of about 39 s (50-300 keV).
The time-averaged spectrum from T0-2 s to T0+39 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is 0.30 +/- 0.19 and
the cutoff energy, parameterized as Epeak, is 148 +/- 15 keV.

The event fluence (10-1000 keV) in this time interval is
(3.02 +/- 0.24)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0 in the 10-1000 keV band
is 1.56 +/- 0.17 ph/s/cm^2.


The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"