GRB 210228A: GECAM detection

During the commissioning phase, GECAM-B triggered a long burst, GRB 210228A, at 2021-02-28T06:38:32.600 UTC (denoted as T0), which was also detected by Fermi/GBM (Trig# 636187116) and CALET/CGBM (Trig# 1298529456). 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 a broad pulse with a duration of about 40 s. An automatic on-ground localization was calculated using the light curves and spectrum. 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: 85.5 deg Dec: -41.8 deg Err: 2.1 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/gecamb_lc_grd_all_combine_68193512.png The GECAM preliminary location could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_skymap_bdm_68193512_V01.png This burst is temporally and positional coincident with Fermi/GBM trigger (trig# 636187116). 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).