GRB 221121A

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

At 06:34:49 UT on 21 Nov 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 221121A (trigger 690705294.743784 / 221121274).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 168.8, Dec = 71.1 (J2000 degrees, equivalent to J2000 11h 15m, 71d 05'), with a statistical uncertainty of 1.1 degrees.

The angle from the Fermi LAT boresight is 18.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221121274/quicklook/glg_skymap_all_bn221121274.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221121274/quicklook/glg_healpix_all_bn221121274.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221121274/quicklook/glg_lc_medres34_bn221121274.gif

R. Gopalakrishnan (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. 
Bhalerao (IITB), D. Bhattacharya (Ashoka University/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 the detection of a long GRB221121A which was 
also detected by Fermi GBM (GCN Circ. 32960
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 ).

The source was clearly detected in the 20-200 keV energy range. The 
light curve peaks at 2022-11-21 06:34:50.5 UTC. The measured peak count 
rate associated with the burst is 173 (+42, -40) counts/s above the 
background in the combined data of all quadrants, with a total of 1531 
(+490, -529) counts. The local mean background count rate was 532 (+3, 
-4) counts/s. Using cumulative rates, we measure a T90 of 22 (+15, -9) 
s.

It was also clearly detected in the CsI anticoincidence (Veto) detector 
in the 100-500 keV energy range. The light curve peaks at 2022-11-21 
06:34:53.9 UTC. The measured peak count rate is 283 (+79, -30) counts/s 
above the background in the combined Veto data of all quadrants, with a 
total of 3488 (+696, -662) counts. The local mean background count rate 
was 1746 (+6, -6) counts/s. We measure a T90 of 22 (+10, -4) s from the 
cumulative Veto light curve.

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

A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the MGNS/BepiColombo team,

J. Benkhoff on behalf of the BepiColombo team,

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

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

E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB 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 221121A
(Fermi-GBM detection: Fermi GBM Team, GCN Circ. 32960
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 ;
AstroSat-CZTI detection: Gopalakrishnan et al., GCN Circ. 32969
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 )
has been detected by Fermi (GBM trigger 690705294), Konus-Wind,
INTEGRAL (SPI-ACS), AstroSat (CZTI), CALET (CGBM), GECAM-B
(trigger tn221121_063449_fb), Swift (BAT), and BepiColombo (MGNS),
so far, at about 23690 s UT (06:34:50).
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:
  163.104 (10h 52m 25s) +69.356 (+69d 21' 22")
 Corners:
  164.660 (10h 58m 38s) +69.887 (+69d 53' 12")
  164.681 (10h 58m 43s) +70.133 (+70d 08' 00")
  161.617 (10h 46m 28s) +68.809 (+68d 48' 31")
  161.623 (10h 46m 30s) +68.558 (+68d 33' 29")
 ---------------------------------------------
The error box area is 952 sq. arcmin, and its maximum
dimension is 1.9 deg (the minimum one is 9 arcmin).
The Sun distance was about 103 deg.

This localization may be improved.

The IPN localization is consistent with, but reduces the area of,
the Fermi-GBM final localization (GCN Circ. 32960
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 ).

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB221121_T23691/IPN

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

T. Sakamoto, A. Yoshida,  S. Sugita (AGU), Y. Kawakubo (LSU), 
K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), Y. Asaoka (ICRR),
S. Torii, Y. Akaike, K. Kobayashi (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC),
M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

The long GRB 221121A (Fermi GBM Final Real-time Localization:
Fermi GBM team, GCN Circ. 32960
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 ; AstroSat CZTI detection:
Gopalakrishnan et al., GCN Circ 32969
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 ; IPN triangulation: 
Kozyrev etc al., GCN Circ. 32971
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 ) triggered the CALET Gamma-ray
Burst Monitor (CGBM) at 06:34:47.10 UTC on 21 November 2022
(http://cgbm.calet.jp/cgbm_trigger/flight/1353047657/index.html).
The burst signal was seen by only SGM detector.

The burst light curve shows a single pulse which starts
at T+2.6 sec, peaks at T+3.1 sec, and ends at T+30.2 sec.
The T90 and T50 durations measured by the SGM data are 24.1 +/- 0.8 sec
and 10.1 +/- 1.7 sec (40-1000 keV), respectively.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1353047657/

The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at the Waseda University.