TITLE:   GCN CIRCULAR
NUMBER:  29783
SUBJECT: GRB 210409A: GECAM detection
DATE:    21/04/10 12:46:14 GMT
FROM:    Chao Zheng at IHEP  <zhengchao97@ihep.ac.cn>

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

During the commissioning phase, GECAM-B triggered a long burst,
GRB 210409A, at 2021-04-09T21:28:07.950 UTC (T0) from the ground search.
There is a weak precursor, by which the ground search found this burst,
~20 s before the main burst, which triggered GECAM-B in-flight as well.

According to the GECAM-B light curves in about 8 keV - 500 keV, 
this burst mainly consists of multiple pulses with duration of about 37 s.
Spectral evolution is clearly seen during the burst, and the emissions
in low energies last longer than that in high energies.

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: 70.9 deg 
Dec: -58.3 deg 
Err: 2.9 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/multiLCvsE_tn210409_212807.pdf

The GECAM preliminary location could be found here:  
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_skymap_bdm_71702907_V01.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).