TITLE:   GCN CIRCULAR
NUMBER:  29392
SUBJECT: GRB 210204A: GECAM detection
DATE:    21/02/04 07:51:58 GMT
FROM:    Shaolin Xiong at IHEP  <xiongsl@ihep.ac.cn>

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

During the commissioning phase, GECAM-B in-flight triggered (Trig#
66119400) a long burst, GRB 210204A, at 2021-02-04T06:30:00.600 UTC (T0),
which was also reported by Fermi/GBM (GCN 29390) and
CALET/CGBM (Trig# 1296455384).

GECAM 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
multiple pulses, while the later bright pulse is evident in the alert data
although it falls in the last wide time bin.
The burst spectrum extends above about 400 keV.

An automatic on-ground localization was calculated using the light curves
and spectrum in the alert data.
Although the in-flight calibration of energy response and
localization has not been finalized yet, GECAM-B localized this burst to
the following position (J2000):
Ra: 121.7 deg  Dec: 1.5 deg
Err: 7.5 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-B location is consistent with the Fermi/GBM position (GCN 29390,
29391) within error.

The GECAM light curve could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_lc_grd_all_combine_66119400.png

The GECAM preliminary on-ground location could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_skymap_bdm_66119400_V01.png

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).