GCN Circular 31331

G. Y. Zhao, S. L. Xiong, X. L. Zhang , S. Xiao, C. Cai, J. J. He, Y. Huang,
Z. W. Guo, 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 
burst, GRB 211229A, at 2021-12-29T03:30:05.200 UTC (denoted as T0),
which was also observed by Fermi/GBM (GCN #31329
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 ).
 
GECAM alert data was downlinked to the ground through the short message
service of BeiDou Navigation Satellite System (BDS) within ~60 s after T0.

According to the BDS alert data, this burst mainly consists of a broad pulse
with a duration of about 50 s. 

The GECAM light curve could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_lc_grd_all_combine_94447805.png

Using the automatic on-ground localization pipeline with the BDS alert data, 
GECAM-B localized this burst to the following position (J2000): 
Ra:  302.7 deg 
Dec: 27.5 deg
Err: 8.7 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 location is very close to SGR J1935+2154 and cannot be ruled out as 
originating from it. The GECAM preliminary location could be found here: 
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_skymap_fit_94447805.png

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).