TITLE:   GCN CIRCULAR
NUMBER:  31345
SUBJECT: GRB 211231A: GECAM detection
DATE:    21/12/31 14:40:56 GMT
FROM:    Xiaolu Zhang at IHEP  <xlzhang@ihep.ac.cn>

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

During the commissioning phase, GECAM-B was triggered in-flight by a 
long bright burst, GRB 211231A, at 2021-12-31T07:00:35.050 UTC (denoted as T0)，
which was also observed by Fermi/GBM (GCN #31343).

According to the BDS alert data, this burst mainly consists of a broad pulse
with a duration of about 15 s.

The GECAM light curve could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/GRB211231Alc.png

An automatic on-ground localization was calculated using the light curves
and spectrum. 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: 295.1 deg
dec: -7.0 deg
err: 5.0 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. 

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).