GRB 211120, GRB 211120B

R. Dunwoody (UCD), J.Mangan (UCD) and C.Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 13:09:46.84 UT on 20 November 2021, the Fermi Gamma-Ray Burst Monitor
(GBM)
triggered and located GRB 211120B (trigger 659106591 / 211120548).
which was also detected by the Swift/BAT-GUANO (DeLaunay et al. 2021, GCN
31101
Loading...
 
 )

The GBM on-ground calculated location, using the GBM trigger
data, is RA = 47.9, DEC = 47.1 (J2000 degrees,
equivalent to 03 h 11 m, 47 d 6 '), with a statistical uncertainty
of 1.9 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 62
degrees.

The GBM light curve consists of a single peak
with a duration (T90) of about 36.1 s (50-300 keV).
The time-averaged spectrum from T0-6.400 s to T0+33.537 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.99 +/- 0.04 and
the cutoff energy, parameterized as Epeak, is 298.2 +/- 26.3 keV

The event fluence (10-1000 keV) in this time interval is
(1.184 +/- 0.60)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.28 s in the 10-1000 keV band
is 6.5 +/- 0.2 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 180.1 +/- 24.3 keV, alpha = -0.79 +/- 0.08 and beta = -1.87 +/-
0.08.

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/"

James DeLaunay (UAlabama), Gayathri Raman (PSU), Aaron Tohuvavohu (U
Toronto), Jamie A. Kennea (PSU), report:

Swift/BAT did not successfully trigger on GRB 211120B (T0: 2021-11-20
13:09:46.8 UT, Fermi Trigger: 659106591).

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,
arXiv:2111.01769
Loading...
 
 ), detects the burst with a sqrt(TS) of 23.1 in a
8.192 s analysis time bin.
The estimated T90 in the detector is 24.5 s (15-350 keV).

NITRATES prefers an origin for this burst coming from outside the
coded FOV, with DeltaLLHOut of -6.

See Section 9.1 and Figure 20 in the NITRATES paper for brief
descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and
DeltaLLHOut.

An out of FOV origin is consistent with the Fermi/GBM localization.

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/