TITLE:   GCN CIRCULAR
NUMBER:  30070
SUBJECT: GRB 210522A: GECAM detection
DATE:    21/05/23 16:33:25 GMT
FROM:    Shuo Xiao at IHEP  <xiaoshuo@ihep.ac.cn>

C. Y. Li, S. Xiao, S. L. Xiong, X. Y. Zhao, X. Y. Song, Y. Huang,
C. Cai, Y. Zhao, Q. B. Yi, J. C. Liu, Y. Q. Zhang, W. C. Xue, C. Zheng,
Z. W. Guo, X. L. Zhao, B. X. Zhang, C. W. Wang, S. L. Xie,
P. Wang, X. B. Li, W. X. Peng, R. Qiao, J. Wang, H. S. Zhao,
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 hard GRB,
GRB 210522A, at 2021-05-22T22:11:44.450 UTC (denoted as T0), 
which was also observed by CALET/GBM, INTEGRAL/SPI-ACS and Konus-WIND.

According to the GECAM-B light curves in about 8 keV-4 MeV, 
this burst mainly consists of multiple pulses with a duration of about 50s.

The GECAM light curve could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_grd_75420704.45.png

GECAM-B localized this burst to the following position (J2000):
Ra: 90.06 deg
Dec: 1.36 deg
Err: 1.19 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. 

In addition, we derived a triangulation location for this burst using
GECAM-B data together with public data of INTEGRAL-SPI/ACS and Konus-WIND,
based on a novel method (S. Xiao, et al., submitted). 
Although there are two intersection regions of triangulation annuli, only one
region is consistent with the above location given by GECAM-B alone, thus is
the final location region (3-sigma), which could be defined as (J2000):
        Ra (deg)  Dec (deg)
Center  85.78, 2.09
Corner
        83.67, 0.30
        79.45, 2.09
        90.00, 2.69
        87.89, 3.88

The location map could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/location_gecamb_grd_75420704.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).

We are very grateful for the public data of INTEGRAL-SPI/ACS and Konus-WIND.