TITLE: GCN CIRCULAR NUMBER: 31803 SUBJECT: GRB 220320A: Detection by VZLUSAT-2 DATE: 22/03/29 04:06:06 GMT FROM: Jakub Ripa at Masaryk University ripa.jakub@mail.muni.cz

J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), M. Ohno (Eotvos U./Hiroshima U.),  N. Werner  (Masaryk U.),  L. Meszaros (Konkoly Observatory), H. Takahashi (Hiroshima U.), B. Csak (Konkoly Observatory), M. Topinka, F. Munz, F. Hroch (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory),  T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU)  -- the VZLUSAT-2/GRB payload collaboration.

The bright, long-duration GRB 220320A (AstroSat-CZTI detection: Gopalakrishnan et al., GCN Circ. 31779; localized by IPN: Kozyrev et al. GCN Circ. 31783 and detected also by Fermi/GBM trigger 669443999, CALET/CGBM trigger 1331786356, Konus-Wind, INTEGRAL/SPI-ACS at about 04:39:54 UT) was also detected by one of the two GRB detectors on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/).

This is the first time that a GRB was observed by the VZLUSAT-2 3U CubeSat.

The data acquisition was performed by GRB detector unit no. 1 (the unit no. 0 was turned off). The detector was performing a several hours long background monitoring survey with 15 s temporal resolution, which is not optimal for GRB search. Much finer resolution is planned for the nominal operation. The 46 sigma detection significance was confirmed at around 04:39:55 UTC.

The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB220320A_GCN_VZLUSAT_2.pdf

GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSats constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral.