GRB 210121A

W. C. Xue, C. Cai, J. C. Liu, Q. Luo, S. Xiao, 
Q. B. Yi, Y. Q. Zhang, C. Zheng, 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 2021-01-21T18:41:48.750 (T0), Insight-HXMT/HE detected 
GRB 210121A (trigger ID: HEB210121779) in a routine search of the data.

The Insight-HXMT/HE light curve mainly consists of multiple
pulses with a duration (T90) of 13.24 s measured from T0+0.27 s. 
The 1-ms peak rate, measured from T0+0.52 s, is 10996 cnts/sec. 
The total counts from this burst is 45848 counts. 
URL_LC: http://twiki.ihep.ac.cn/pub/HXMT/GRBList/HEB210121779_lc.jpg

All measurements above are made with the CsI detectors operating in the 
GRB mode with the energy range of about 80-800 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.

W. X. Peng, S. Xiao, C. Cai, Y. Zhao, P. Wang, S. L. Xiong,
Z. H. An, C. Chen, G. Chen, W. Chen, M. Gao, K. Gong, D. Y. Guo,
J. J. He, Y. Huang, B. Li, C. Li, C. Y. Li, J. H. Li, Q. X. Li,
X. B. Li, X. Q. Li, Y. G. Li, X. H. Liang, J. Y. Liao, J. C. Liu,
X. J. Liu, Y. Q. Liu, F. J. Lu, Q. Luo, X. Ma, G. Ou, R. Qiao,
D. L. Shi, J. Y. Shi, L. M. Song, X. Y. Song, G. X. Sun, X. L. Sun,
Y. L. Tuo, C. W. Wang, J. Z. Wang, X. Y. Wen, Y. B. Xu, Y. P. Xu,
W. C. Xue, S. Yang, M. Yao, Q. B. Yi, C. Y. Zhang, D. L. Zhang, Fan Zhang,
Fei Zhang, H. M. Zhang, K. Zhang, P. Zhang, S. N. Zhang, Y. Q. Zhang,
Z. Zhang, S. Y. Zhao, X. Y. Zhao, C. Zheng, S. J. Zheng, X. Zhou (IHEP),
report on behalf of GECAM team:

During the commissioning phase, GECAM-B was triggered by a long GRB 210121A
at 2021-01-21T18:41:48.800 UTC (denoted as T0), which was also observed by
Insight-HXMT/HE (GCN # 29346) and Konus-Wind.

According to the GECAM-B light curves in about 8 keV-4 MeV,
this burst mainly consists of multiple pulses with T90 of 15.0 +/- 0.3 s
measured from T0+0.20 s. The 1-s peak counts rate is about 13108 cps
while the total counts is about 109051 counts.

Spectral evolution is clearly detected during the burst, and
the emissions in low energies last longer than that in high energies.

Although the in-flight calibration of energy response and localization
has not been finalized yet,
GECAM-B localized this burst to the following position (J2000):
Ra: 23.3 deg
Dec: -47.7 deg
Err: 2.0 deg (1-sigma, statistical only)
The current systematic error of location is estimated to be several degrees
which could be minimized by the ongoing calibration.

The GECAM light curve could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/utn210121_184148_GECAMb.pdf

Please note that all GECAM results here are preliminary. The final analysis
will be published in journal papers or GECAM online catalog.

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor
(GECAM) mission consists of two small satellites (GECAM-A and GECAM-B) in
Low Earth Orbit (600 km, 29 deg), launched on Dec 10, 2020 (Beijing Time),
which was funded by the Chinese Academy of Sciences (CAS).

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 long-duration, bright GRB 210121A
(Insight-HXMT/HE detection: Xue et al., GCN Circ. 29346
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GECAM detection: Peng et al., GCN Circ. 29347
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 )
has been detected by Konus-Wind, Mars-Odyssey (HEND),
INTEGRAL (SPI-ACS), Insight (HXMT/HE), and GECAM, so far,
at about 67309 s UT (18:41:49).

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
    16.981 (01h 07m 55s) -46.401 (-46d 24' 04")
  Corners:
    17.388 (01h 09m 33s) -46.452 (-46d 27' 06")
    17.369 (01h 09m 29s) -46.539 (-46d 32' 20")
    16.575 (01h 06m 18s) -46.348 (-46d 20' 54")
    16.595 (01h 06m 23s) -46.261 (-46d 15' 40")
  ---------------------------------------------
The error box area is 181 sq. arcmin, and its maximum
dimension is 36 arcmin (the minimum one is 5 arcmin).
The Sun distance was 64 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB210121_T67306/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 long-duration, bright GRB 210121A
(Insight-HXMT/HE detection: Xue et al., GCN Circ. 29346
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GECAM detection: Peng et al., GCN Circ. 29347
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 ;
IPN triangulation: Hurley et al., GCN Circ. 29348
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 )
triggered Konus-Wind at T0=67306.174 s UT (18:41:46.174).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.1 s and has a total duration of ~64 s.
The emission is seen up to ~7 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210121_T67306/

As observed by Konus-Wind, the burst
had a fluence of 1.18(-0.10,+0.10)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+1.072 s,
of 3.00(-0.43,+0.43)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+22.784 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.59(-0.05,+0.06),
the high energy photon index beta = -3.03(-1.42,+0.43),
the peak energy Ep = 875(-69,+70) keV
(chi2 = 110/97 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 s to T0+1.792 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.32(-0.08,+0.09),
the high energy photon index beta = -3.60(3.60,+0.68),
the peak energy Ep = 981(-88,+94) keV
(chi2 = 82/97 dof).

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