GRB 181121A

*A.Ursi (INAF/IAPS), F. Verrecchia (SSDC, and INAF/OAR), *


*N. Parmiggiani (INAF/IASF-Bo), A. Argan, M. Cardillo, Y. Evangelista, G.
Minervini, G. Piano (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ. Roma Tor
Vergata), F. Lucarelli, C. Pittori, (SSDC, and INAF/OAR), A. Bulgarelli, V.
Fioretti, F. Fuschino (INAF/IASF-Bo), M. Marisaldi (INAF/IASF-Bo, and
Bergen University), M. Pilia, A. Trois (INAF/OA-Cagliari), I. Donnarumma
(ASI), F. Longo (Univ. Trieste and INFN Trieste), A. Giuliani
(INAF/IASF-Mi) report on behalf of the AGILE Team:The AGILE
Mini-CALorimeter (MCAL) detected a short burst at T0 = 2018-11-21
20:43:36.283 +/- 0.01 s (UTC).*
*The light curve shows a sharp peak lasting about 0.16 s, that released a
total number of ~334 counts in the detector (in the 0.4-100 MeV energy
range), above an average background rate of 573 counts / s. Two weaker
pulses are present at T0+0.32 s and T0+0.67 s*

*.*
*The GRB is clearly detected also by AGILE scientific ratemeters; in
particular, by the Super-AGILE (20-60 keV), **Anti-Coincidence (50-200
keV), and MCAL (0.4-100 MeV) ratemeters.*



*Further analysis is still in progress.The AGILE-MCAL detector has a full
solid angle acceptance, and is operational in the range 0.4 - 100 MeV.*

V. Sharma and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data showed the detection of a short GRB 181121A, which was also detected by AGILE/MCAL detection (Ursi A. et al., GCN 23429
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 ).

The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with strongest peak at 20:43:36.500 UT. The measured peak count rate is 1131.6 cts/s above the background in combined data of four quadrants, with a total of 1279 cts. The local mean background count rate was 477 cts/s. Using cumulative rates, we measure a T90 of 1.4 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. 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.

A. Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks, D. Svinkin,
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,

and A. Ursi, N. Parmiggiani, F. Verrecchia, A. Bulgarelli,
A. Trois, M. Marisaldi, C. Pittori, M. Tavani, Y. Evangelista,
I. Donnarumma, M. Cardillo, G. Piano, G. Minervini, A. Argan,
F. Lucarelli, A. Zoli, V. Fioretti, F. Fuschino, M. Pilia,
F. Longo, A. Giuliani on behalf of the AGILE team report:

The short-duration GRB 181121A (Ursi et al., GCN Circ. 23429
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 ) was
detected by Konus-Wind, INTEGRAL (SPI-ACS), and AGILE (MCAL), at
about 74617 s UT (20:43:37).

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
 ---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
   14.424 (00h 57m 42s) -11.977 (-11d 58' 38")
 Corners:
   11.772 (00h 47m 05s)  -9.257 ( -9d 15' 24")
   13.883 (00h 55m 32s) -11.751 (-11d 45' 05")
   17.495 (01h 09m 59s) -14.686 (-14d 41' 10")
   14.969 (00h 59m 53s) -12.200 (-12d 12' 00")
 ---------------------------------------------
The error box area is 1.6 sq. deg, and its maximum
dimension is 7.8 deg (the minimum one is 29 arcmin).
The Sun distance was 126 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB181121_T74619/IPN

The time history and spectrum will be given in forthcoming
GCN Circulars.

A. Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks,
M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:

The short-duration GRB 181121A
(AGILE/MCAL detection: Ursi et al., GCN 23429
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 ;
AstroSat CZTI detection: Sharma et al., GCN 23447
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 ;
IPN Triangulation: Kozlova et al., GCN 23449
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 )
triggered Konus-Wind at T0=74619.153 s UT (20:43:39.153).

The burst light curve shows a multipeaked structure
which starts at ~T0 s and has a total duration of ~1.4 s.
The emission is seen up to ~2 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.46(-0.26,+0.44)x10^-5 erg/cm2,
and a 16-ms peak flux, measured from T0+0.118 s,
of 9.44(-1.53,+1.77)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 2 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.83(-0.20,+0.46),
the high energy photon index beta = -2.58(-1.04,+0.46),
the peak energy Ep = 226(-65,+45) keV
(chi2 = 72/56 dof).

The spectrum near the maximum count rate
(measured from T0+0.064 to T0+0.192 s)
is best fit in the 20 keV - 2 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.27(-0.24,+0.32),
the high energy photon index beta = -2.54(-0.47,+0.28),
the peak energy Ep = 271(-47,+50) keV
(chi2 = 57/42 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB181121_T74619/

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.