TITLE: GCN CIRCULAR NUMBER: 31339 SUBJECT: GRB 211229B: GECAM detection DATE: 21/12/30 03:35:18 GMT FROM: Guoying Zhao at IHEP gyzhao@ihep.ac.cn

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 bright burst, GRB 211229B, at 2021-12-29T22:18:43.150 UTC (denoted as T0)， which was also observed by Fermi/GBM (GCN #31336).

This burst mainly consists of multiple pulses with duration of about 15 s.

The GECAM light curve could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/211229B_LightCurve.png

The GECAM preliminary location could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/SkyMap.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).