TITLE:   GCN CIRCULAR
NUMBER:  29347
SUBJECT: GRB 210121A: GECAM detection
DATE:    21/01/23 15:34:41 GMT
FROM:    Shaolin Xiong at IHEP  <xiongsl@ihep.ac.cn>

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).