TITLE: GCN CIRCULAR NUMBER: 27815 SUBJECT: GRB200521A: ASIM observation DATE: 20/05/25 09:18:56 GMT FROM: Martino Marisaldi at U of Bergen, Norway M. Marisaldi (University of Bergen), A. Mezentsev (University of Bergen), N. Østgaard (University of Bergen), V. Reglero (University of Valencia) and T. Neubert (DTU Space) report on behalf of the ASIM Team: At 12:16:39.798 UT on 21 May 2020, the Atmosphere-Space Interactions Monitor (ASIM) mission triggered on the bright short hard GRB 200521A (AGILE detection: Verrecchia et al., GCN Circ. 27776; CALET-GBM detection: Yoshida et al., GCN Circ. 27777; CGBM-SPI-ACS triangulation: Sakamoto et al., GCN Circ. 27790; IPN triangulation: Svinkin et al., GCN Circ. 27795; Konus-Wind detection: Svinkin et al., GCN Circ. 27796) Photon by photon data with <1 microsecond time resolution have been collected for a time interval of two seconds centered at the trigger time. As seen by the Modular X- and Gamma-Ray Sensor (MXGS) onboard ASIM the burst consists of a single bright peak about 300 ms in duration. The emission is detected in the MXGS High Energy Detector (HED), sensitive in the range 0.3 to >30 MeV. Significant emission is observed up to several MeV. The MXGS Low Energy Detector (LED), sensitive in the range 0.05 to 0.4 MeV, was not active at trigger time. ASIM is an ESA mission onboard the International Space Station dedicated to the observation of Terrestrial Gamma-ray Flashes (TGFs) and Transient Luminous Events (TLEs) operative since June 2018 (Neubert et al., Space Sci Rev (2019) 215:26 https://doi.org/10.1007/s11214-019-0592-z ). The payload includes the Modular X- and Gamma-Ray Sensor (MXGS) (Østgaard et al., Space Sci Rev (2019) 215:23 https://doi.org/10.1007/s11214-018-0573-7 ), and the the Modular Multispectral Imaging Array (MMIA) (Chanrion et al., Space Sci Rev (2019) 215:28 https://doi.org/10.1007/s11214-019-0593-y ). The ASIM Science Data Centre (ASDC) website is https://asdc.space.dtu.dk/