TITLE: GCN CIRCULAR NUMBER: 30922 SUBJECT: GECAM observation of a burst from SGR J1555.2-5402 DATE: 21/10/05 14:17:18 GMT FROM: Y Q Zhang at IHEP yqzhang@ihep.ac.cn

Y. Q. Zhang, S. L. Xiong, S. Xiao, C. Cai, X. Y. Zhao, Y. Huang, X. Y. Song, J. C. Liu, S. L. Xie, Y. Zhao, Z. W. Guo, C. Zheng, W. C. Xue, 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, X. L. Zhang, L. M. Song, F. J. Lu, S. N. Zhang (IHEP), report on behalf of GECAM team:

During the commissioning phase, GECAM-B was triggered on-ground by a bright short burst from SGR J1555.2-5402 at 2021-10-04T00:13:14.700 UTC (T0).

According to the GECAM-B light curves in about 10-50 keV, this burst mainly consists of a single pulse with a duration about 30 ms.The location given by GECAM-B alone is consistent with SGR J1555.2-5402 within the error.

GECAM-B localized this burst to the following position (J2000): Ra: 241.96 deg Dec: -55.45 deg Err: 9.01 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 GECAM light curve could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/utn211004_001314_GECAMb.png

According to our multiple-mission joint location pipeline (S. Xiao et al., accepted by ApJ) using GECAM-B and Fermi/GBM data, this burst is localized to an annulus which is very consistent with SGR J1555.2-5402.

The GECAM-GBM joint location could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/SGR20211004T001314.700-JointLoc.pn...

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).