GCN Circular 36528

Yue Wang, Shao-Lin Xiong, Chen-Wei Wang report on behalf of the GECAM team:

GECAM-B was triggered both in-flight and on-ground by a long burst, GRB 240521A, at 2024-05-21T07:32:12.550 UTC (T0). 

According to the realtime alert data, the GECAM-B light curve shows a long pulse with a duration of ~15 sec (15-1020 keV). 

The time-averaged spectrum of GECAM-B realtime data from about T0-1 to T0+9 s could be
adequately fit by a cut-off power-law with a flux about 3.30E-7 erg/cm^2/s in 20-1000 keV.

The GECAM light curve could be found here: 
https://twikinew.ihep.ac.cn/pubgecam/Sandbox/GRB/GRB240521A_lightcurve.jpg

Using the automatic on-ground localization pipeline with the BDS alert data, 
GECAM-B localized this burst to the following position (J2000): 
Ra:  199.2 deg 
Dec:   78.8 deg
Err:   2.8 deg (1-sigma, statistical only)

The GECAM preliminary location could be found here:  
https://twikinew.ihep.ac.cn/pubgecam/Sandbox/GRB/GRB240521A_location.jpg

We note that these results are based on realtime alert data and thus very preliminary. Refined analysis will be reported later.

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM) mission originally consists of two microsatellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).