TITLE: GCN CIRCULAR NUMBER: 42984 SUBJECT: GRB 251129B: GECAM-B observation of a burst DATE: 25/12/04 08:30:50 GMT FROM: xueyuan zao zaoxueyuan@gmail.com

Xue-Yuan Zao, Yue Wang, Zheng-Hang Yu, Chen-Wei Wang, Chao Zheng, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:

GECAM-B was triggered in-flight and on-ground by a short/hard burst GRB 251129B at 2025-11-29T09:51:34.250 UTC (denoted as T0). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse main emission with a duration (T90) of 0.25 +0.10/-0.15 s.

The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251129B.png

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).

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