The Complete Catalog of Gamma-Ray Transients Observed by GRBAlpha & VZLUSAT-2 CubeSat Missions

Marianna Dafcikova; Jakub Ripa; Andras Pal; Norbert Werner; Michaela Duriskova; Yasushi Fukazawa; Martin Kolar; Laszlo Meszaros; Filip Munz; Masanori Ohno; Lea Szakszonova; Hiromitsu Takahashi; Masato Yokota; Jean-Paul Breuer; Hsiang-Kuang Chang; Balazs Csak; Vladimir Daniel; Juraj Dudas; Marcel Frajt; Gabor Galgoczi; Peter Hanak; Filip Hroch; Chin-Ping Hu; Jan Hudec; Nikola Husarikova; Yuto Ichinohe; Jakub Kapus; Miroslav Kasal; Martin Koleda; Robert Laszlo; Chih-Hsun Lin; Tsung-Che Liu; Tsunefumi Mizuno; Kazuhiro Nakazawa; Hirokazu Odaka; Michal Pazderka; Ales Povalac; Maksim Rezenov; Martin Sabol; Kaustubha Sen; Miroslav Smelko; Petr Svoboda; Martin Topinka; Che-Chih Tsao; Tomas Urbanec; Ivo Vertat; Tomas Vitek; Chih-En Wu

arXiv · 2607.17971

The Complete Catalog of Gamma-Ray Transients Observed by GRBAlpha & VZLUSAT-2 CubeSat Missions

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Abstract

We present the largest sample of gamma-ray transients observed by any CubeSat mission so far. Observations were acquired by a 1U CubeSat GRBAlpha, the smallest astrophysical space observatory, and a 3U CubeSat VZLUSAT-2. Both missions were technological pathfinders and carried a novel CsI scintillator-based detector read-out by silicon photomultipliers. They operated on Sun-synchronous low Earth orbits below 550 km for about four years; GRBAlpha between March 2021 and June 2025 while VZLUSAT-2 between January 2022 and November 2025. Despite being technological experiments, they observed over 300 gamma-ray transients including gamma-ray bursts (GRBs), solar flares, soft gamma repeaters and one outburst from an X-ray binary. Among these are the two brightest GRBs ever observed, GRB 221009A and GRB 230307A, without saturation and GRBs at redshifts up to z=4.2. GRBAlpha also contributed to the InterPlanetary Network. Regular monitoring of transients was demonstrated by a detection rate of two transients or one GRB a week and the shortest time between two subsequent detections of only 42 minutes. We show that a constellation of nanosatellites around the Earth would observe at least 60% of Fermi/GBM GRBs with 5$\sigma$ significance and over 90% at 3$\sigma$ level. GRBAlpha and VZLUSAT-2 prove that routine monitoring of the gamma-ray sky can also be done by low-cost and quickly developed nanosatellite missions.

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Marianna Dafcikova, Jakub Ripa, Andras Pal, Norbert Werner, Michaela Duriskova, Yasushi Fukazawa, Martin Kolar, Laszlo Meszaros, Filip Munz, Masanori Ohno, Lea Szakszonova, Hiromitsu Takahashi, Masato Yokota, Jean-Paul Breuer, Hsiang-Kuang Chang, Balazs Csak, Vladimir Daniel, Juraj Dudas, Marcel Frajt, Gabor Galgoczi, Peter Hanak, Filip Hroch, Chin-Ping Hu, Jan Hudec, Nikola Husarikova, Yuto Ichinohe, Jakub Kapus, Miroslav Kasal, Martin Koleda, Robert Laszlo, Chih-Hsun Lin, Tsung-Che Liu, Tsunefumi Mizuno, Kazuhiro Nakazawa, Hirokazu Odaka, Michal Pazderka, Ales Povalac, Maksim Rezenov, Martin Sabol, Kaustubha Sen, Miroslav Smelko, Petr Svoboda, Martin Topinka, Che-Chih Tsao, Tomas Urbanec, Ivo Vertat, Tomas Vitek, Chih-En Wu. 2026-07-20. The Complete Catalog of Gamma-Ray Transients Observed by GRBAlpha & VZLUSAT-2 CubeSat Missions. https://arxiv.org/abs/2607.17971

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