GRB 231123B

The Fermi GBM team reports the detection of a likely LONG GRB

At 19:25:21 UT on 23 Nov 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 231123B (trigger 722460326.50637 / 231123809).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 160.4, Dec = -68.9 (J2000 degrees, equivalent to J2000 10h 41m, -68d 54'), with a statistical uncertainty of 6.1 degrees.

The angle from the Fermi LAT boresight is 104.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231123809/quicklook/glg_skymap_all_bn231123809.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231123809/quicklook/glg_healpix_all_bn231123809.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231123809/quicklook/glg_lc_medres34_bn231123809.gif

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

Swift/BAT did not localize GRB 231123B onboard (T0: 2023-11-23T19:25:21.51 UTC, Fermi trig 722460326) 

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 90 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 8.8 in a 8.192 s analysis time bin, starting at T0 - 4.096 s. 

NITRATES results are consistent with a burst coming from outside the FOV, with DeltaLLHOut of 0.4.

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/

S. Dalessi (UAH), S. Lesage (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 19:25:21.51 UT on 23 November 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 231123B (trigger 722460326/231123809).
which was also detected by Swift/BAT-GUANO (J. DeLaunay et al. 2023, GCN 35195
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 ).
The Fermi Final Localization was reported in GCN 35170
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 .

The angle from the Fermi LAT boresight is 104 degrees.

The GBM light curve single peak with a duration (T90)
of about 77 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+76.802 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.2 +/- 0.2 and the cutoff energy,
parameterized as Epeak, is 160 +/- 38 keV.

The event fluence (10-1000 keV) in this time interval is
(5.9 +/- 0.7)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.5 s in the 10-1000 keV band is 1.9 +/- 0.3 ph/s/cm^2.

The spectrum is also well fit a Band function with Epeak = 115 +/- 44 keV,
alpha = -1.05 +/- 0.28, and beta = -2.16 +/- 0.31.

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/"