TITLE:   GCN CIRCULAR
NUMBER:  29363
SUBJECT: GECAM detection of a short burst probably from SGR 1935+2154
DATE:    21/01/27 08:14:10 GMT
FROM:    Shaolin Xiong at IHEP  <xiongsl@ihep.ac.cn>

Y. Huang, S. J. Zheng, F. J. Lu, S. N. Zhang, L. M. Song, W. X. Peng,
S. L. Xiong, S. Xiao, C. Cai, X. Y. Zhao, X. Ma, P. Zhang, B. X. Zhang,
Z. H. An, C. Chen, G. Chen, W. Chen, M. Gao, K. Gong, D. Y. Guo,
J. J. He, B. Li, C. Li, C. Y. Li, J. H. Li, Q. X. Li,
X. B. Li, X. Q. Li, Y. G. Li, X. H. Liang, J. Y. Liao, J. C. Liu,
X. J. Liu, Y. Q. Liu, Q. Luo, G. Ou, W. X. Peng, R. Qiao,
D. L. Shi, J. Y. Shi, X. Y. Song, G. X. Sun, X. L. Sun,
Y. L. Tuo, C. W. Wang, J. Z. Wang, P. Wang, X. Y. Wen, Y. B. Xu,
Y. P. Xu, W. C. Xue, S. Yang, M. Yao, Q. B. Yi, C. Y. Zhang,
D. L. Zhang, Fan Zhang, Fei Zhang, H. M. Zhang, K. Zhang,
S. N. Zhang, Y. Q. Zhang, Z. Zhang, S. Y. Zhao, Y. Zhao, C. Zheng,
X. Zhou (IHEP),
report on behalf of GECAM team:

During the commissioning phase, GECAM-B was triggered in-flight by
a short burst (trig# 65429420) at 2021-01-27T06:50:20.750 UTC (T0).
Its alert data was promptly downlinked to the ground through the
short message service of BeiDou Navigation Satellite System (BDS).
The time latency of the first BeiDou message relative to the trigger time
is about 1 minute.

According to the BDS alert data, this burst mainly consists of
two pulses with a duration of roughly 100 ms.
There is no much emission above 100 keV.

The in-flight position (J2000) given by GECAM-B is:
Ra: 291.31 deg Dec: 23.67 deg
Galactic lon: 57.74 deg, lat: 3.63 deg
Err: 2.16 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/gecamb_hrlc_grd_65429420.png

The GECAM preliminary location could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_skymap_65429420.png

According to the location and light curve, we suggest that this burst
is very likely from SGR 1935+2154 which seems to be active recently.

This is the first short trigger of GECAM which downlinked the
high resolution light curve through BDS successfully.

As the detailed science data are downloaded, all analyses would be improved.

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).