GRB 210124B

J. C. Liu, C. Zheng, C. Cai,  Q. Luo, S. Xiao, 
W. C. Xue, Q. B. Yi, Y. Q. Zhang, Y. Huang, C. K. Li, 
G. Li, X. B. Li, J. Y. Liao, X. Y. Song, S. L. Xiong, C. Z. Liu, 
X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, Y. F. Zhang, 
X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), 
T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team:

At 2021-01-24T13:23:48.400 (T0), Insight-HXMT/HE detected 
GRB 210124B (trigger ID: HEB210124558) in a routine search of the data.

The Insight-HXMT/HE light curve mainly consists of multiple 
pulses with a duration (T90) of 0.062 s measured from T0+0.01 s. 
The 1-ms peak rate, measured from T0+0.035 s, is 34250 cnts/sec. 
The total counts from this burst is 988 counts. 
URL_LC: http://twiki.ihep.ac.cn/pub/HXMT/GRBList/HEB210124558_lc.jpg

All measurements above are made with the CsI detectors operating in the 
GRB mode with the energy range of about 250-3000 keV (deposited energy). 
Only gamma-rays with energy greater than about 200 keV can penetrate 
the spacecraft and leave signals in the CsI detectors installed inside 
of the telescope. 

Insight-HXMT is the first Chinese space X-ray telescope, which was 
funded jointly by the China National Space Administration (CNSA) and 
the Chinese Academy of Sciences (CAS). 
More information about it could be found at: 
http://www.hxmt.org.

K. Hurley, on behalf of the IPN,

I. G. Mitrofanov, D. V. Golovin, A. S. Kozyrev, M. L. Litvak,
and A. B. Sanin, on behalf of the HEND-Odyssey GRB team,

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

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

and

W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr,
on behalf of the GRS-Odyssey GRB team, report:

The short-duration, bright GRB 210124B
(Insight-HXMT/HE detection: Liu et al., GCN Circ. 29353
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 )
has been detected by Konus-Wind, Mars-Odyssey (HEND),
INTEGRAL (SPI-ACS), and Insight (HXMT/HE), so far,
at about 48220 s UT (13:23:40).

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   274.333 (18h 17m 20s)  -0.443 ( +0d 26' 36")
  Corners:
   274.258 (18h 17m 02s)  -0.358 ( +0d 21' 29")
   274.313 (18h 17m 15s)  -0.234 ( +0d 14' 01")
   274.409 (18h 17m 38s)  -0.529 ( +0d 31' 43")
   274.354 (18h 17m 25s)  -0.654 ( +0d 39' 15")
  ---------------------------------------------
The error box area is 101 sq. arcmin, and its maximum
dimension is 25 arcmin (the minimum one is 5.4 arcmin).
The Sun distance was 37 deg.

The box has rather low galactic latitude of 7.4 deg, but significant 
emission above ~300 keV provides strong evidence against SGR origin of 
this burst.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB210124_T48224/IPN

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

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

The short-duration, bright GRB 210124B
(Insight-HXMT/HE detection: Liu et al., GCN Circ. 29353
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 ;
IPN triangulatuion: Hurley et al., GCN Circ. 29355
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 ;)
triggered Konus-Wind at T0=48224.368 s UT (13:23:44.368).

The burst light curve shows a multipeaked structure
which starts at ~T0-20 ms and ends at ~T0+40 ms,
followed by a weaker emission seen up to ~T0+170 ms.
The total burst duration is ~0.2 s.
The emission is seen up to ~6 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210124_T48224

As observed by Konus-Wind, the burst
had a fluence of 3.03(-0.71,+0.86)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0-0.006 s,
of 6.16(-2.15,+2.54)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+0.064 s)
is best fit in the 20 keV - 6 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.93(-0.20,+0.25)
and Ep = 1544(-642,+1186) keV (chi2 = 33/20 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -1.5
(chi2 = 33/19 dof).

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

D. Nadella (NITK), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta
(IUCAA), P. Sawant (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,
2020, arxiv:2011.07067) showed detection of the short GRB 210124B, which
was also detected by Insight-HXMT/HE (GCN #29353
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 ) & Konus-Wind (GCN
#29357
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 ).

The source was clearly detected in the 20-200 keV energy range in all
four quadrants. Quadrant D was noisy, and we excluded it from further
analysis. The light curve showed multiple peaks of emission with the
strongest peak at 2021-01-24 13:23:45.43 UT. The measured peak count
rate associated with the burst is 2348 (+928, -540) cts/s above the
background in the combined data of three quadrants, with a total of 88
(+52, -26) cts. The local mean background count rate was 362 (+2, -25)
cts/s. Using cumulative rates, we measure a T90 of 0.07 (+0.35, -0.04)
s.

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.