GCN Circular 29758

W. C. Xue, S. L. Xiong, X. Y. Song, Y. Huang, S. Xiao, C. Cai, Y. Zhao, 
J. C. Liu, Q. B. Yi, Y. Q. Zhang, C. Zheng, Z. W. Guo, X. Y. Zhao, 
P. Wang, X. B. Li, W. X. Peng, R. Qiao, D. Y. Guo, 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 very long burst,
GRB 210401A, at 2021-04-01 23:17:08.000 UTC (T0), which was also detected
by Fermi/GBM (GCN #29739
Not found
 
 
) and Konus-Wind (GCN #29744
Not found
 
 
).

According to the GECAM-B light curves in about 10 keV - 500 keV, 
this burst mainly consists of multiple pulses with duration of about 800 s.

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: 275.3 deg Dec: -29.2 deg 
Err: 5.8 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. 

Given that the location is close to the galactic plane, we cannot rule out
the possibility that this burst originated from a galactic source. 

GECAM location is consistent with that of Fermi/GBM within the error.

The GECAM light curve could be found here: 
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/71018228.0energys.pdf

The GECAM preliminary location could be found here:  
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/tn210401_232014_locationSatB_map.pdf

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).