GRB 211118A

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

Swift/BAT did not trigger on GRB 211118A (T0: 2021-11-18 23:38:14 UT,
Fermi Trigger: 658971499, INTEGRAL/SPI-ACS trigger 9523).

The Fermi + INTEGRAL triggers, 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
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 ), detects the burst with a sqrt(TS) of 27.5 in a
1.024 s analysis time bin.
The estimated T90 in the detector is 3.0 +/- 0.05 s (15-350 keV)

NITRATES prefers an origin for this burst coming from outside the
coded FOV, with DeltaLLHOut of 2.7.

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/

V. Prasad (IUCAA), P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute
(IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao
(IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat
CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al.,
2021, JApA, 42, 73) showed detection of GRB 211118A, which was also
detected by Swift/BAT-GUANO (Raman et al., GCN 31096
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 ).

The source was clearly detected in the 20-200 keV energy range. The
light curve showed multiple peaks of emission with the strongest peak at
2021-11-18 23:38:13.65 UT. The measured peak count rate associated with
the burst is 915 (+217, -92) cts/s above the background in the combined
data of two quadrants, with a total of 806 (+94, -109) cts. The local
mean background count rate was 446 (+7, -8) cts/s. Using cumulative
rates, we measure a T90 of 2.2 (+0.6, -0.4) s.

It was also clearly detected in the CsI anticoincidence (Veto) detector
in the 100-500 keV energy range. 

CZTI GRB detections are reported regularly on the payload site at
http://astrosat.iucaa.in/czti/?q=grb [1]. CZTI is built by a TIFR-led
consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC,
and PRL. The Indian Space Research Organisation funded, managed and
facilitated the project.

  

Links:
------
[1] http://astrosat.iucaa.in/czti/?q=grb

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

"At 23:38:14.587 UT on 18 November 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 211118A (trigger 658971499 / 211118985).
which was also detected by the Swift/BAT-GUANO (Raman et al. 2021, GCN 31096
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 ).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 33.7, Dec = 71.1(J2000 degrees, equivalent to J2000 02h 15m, 71d 03'),
with a statistical uncertainty of 2.7 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 127 degrees.

The GBM light curve consists of a single peak
with a duration (T90) of about 7.2 s (50-300 keV).
The time-averaged spectrum from T0-0.002 s to T0+7.776 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.21 +/- 0.07 and
the cutoff energy, parameterized as Epeak, is 2176 +/- 865 keV

The event fluence (10-1000 keV) in this time interval is
(3.975 +/- 0.272)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.064 s in the 10-1000 keV band
is 7.1 +/- 0.5 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/"

A. Ridnaia, S. Golenetskii, D. Frederiks, D. Svinkin,
A. Lysenko, and T. Cline on behalf of the Konus-Wind team,

K. Hurley, on behalf of the IPN,

A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo,
and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

A. Goldstein, M. S. Briggs, and C. Wilson-Hodge
on behalf of the Fermi GBM team,

and

S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu
on behalf of the Swift-BAT team,  report:

The long-duration GRB 211118A
(Swift/BAT-GUANO detection: Raman et al., GCN 31096
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 ;
AstroSat CZTI detection: Prasad et al., GCN 31099
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 ;
Fermi GBM detection: Mangan et al., GCN 31125
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 )
was detected by Fermi (GBM trigger 658971499),
Konus-Wind, INTEGRAL (SPI-ACS), Swift-BAT, and
AstroSat (CZTI) at about 85093 s UT (23:38:13).
The burst was outside the coded field of view of the BAT.

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
 ---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
   26.464 (01h 45m 51s) +73.778 (+73d 46' 40")
 Corners:
   20.795 (01h 23m 11s) +68.534 (+68d 32' 02")
   13.882 (00h 55m 32s) +68.354 (+68d 21' 14")
   39.770 (02h 39m 05s) +78.696 (+78d 41' 47")
   54.289 (03h 37m 09s) +77.757 (+77d 45' 24")
 ---------------------------------------------
The error box area is 28.9 sq. deg, and its maximum
dimension is 14.5 deg (the minimum one is 2.3 deg).
The Sun distance was 120 deg.

This box may be improved.

The IPN localization is consistent with, but reduces the area of, the
Fermi GBM on-ground calculated localization (GCN Circ. 31125
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 ).

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB211118_T85093/IPN

The Konus-Wind time history and spectrum will be given in a forthcoming
GCN Circular.