TITLE: GCN CIRCULAR NUMBER: 31965 SUBJECT: GRB 220423A: Detection by VZLUSAT-2 DATE: 22/04/28 16:36:12 GMT FROM: Jakub Ripa at Masaryk University J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), M. Ohno (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. A long-duration GRB 220423A (AGILE/MCAL detection: Ursi et al., GCN Circ. 31938, Happy Birthday to AGILE!; Swift/BAT detection: Raman et al., GCN Circ. 31943; CALET/CGMB detection: trig. #1334758343; INTEGRAL/SPI-ACS detection: trig. #9870; KONUS-Wind detection: trig. time 2022-04-23 14:14:07.818 UT) was detected by both GRB detector units on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/). The data acquisition was performed by GRB detector units no. 0 and no. 1. The 28 sigma detection significance was confirmed at each detector at 2022-04-23 14:14:14 UTC. The GRB has the T90 duration of 37 s. The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB220423A_GCN_VZLUSAT2.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.