GRB 210401A: GECAM detection

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) and Konus-Wind (GCN #29744). 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).