GCN Circular 30881

C. Zheng, S. L. Xiong, S. Xiao, Y. Q. Zhang, W. C. Xue, X. Y. Song,   
X. Y. Zhao, Y. Huang, S. L. Xie, C. Cai, Y. Zhao, Z. W. Guo, 
X. L. Zhang,  C. Y. Li, C. W. Wang, Q. B. Yi, B. X. Zhang, P. Zhang,
W. X. Peng, R. Qiao, D. Y. Guo, X. B. Li, X. Ma, P. Wang, J. Wang, 
Z. Zhang, S. J. Zheng, W. Chen, J. J. He, G. Y. Zhao, Y. Q. Du,
H. Wu, J. Liang, Q. Luo, J. C. Liu,  L. M. Song, F. J. Lu, 
S. N. Zhang (IHEP), report on behalf of GECAM team:

During the commissioning phase, GECAM-B was triggered in-flight by a long
bright burst, GRB 210925A, at 2021-09-25T19:12:34.600 UTC (denoted as T0),
which was also detected by Fermi/GBM (GCN #30880
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 ).

Its alert data was promptly downlinked to the ground through the short
message service of BeiDou Navigation Satellite System (BDS). The time
latency of the first BeiDou message relative to the trigger time is about
1 minute.

According to the BDS alert data, this burst mainly consists of multiple
pulses with duration of about 10 s. 

The GECAM light curve could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/utn210925_191234_GECAMb.png

An automatic in-flight localization was calculated using the light curves 
and spectrum. Although the in-flight calibration of energy response and l
ocalization has not been finalized yet, GECAM-B localized this burst to 
the following position (J2000): 
Ra: 357.83 deg 
Dec: -24.58 deg
Err: 3.50 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.

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).