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GCN Circular 33847

Subject
GRB 230518B: VZLUSAT-2 detection
Date
2023-05-22T03:38:03Z (a year ago)
From
Marianna Dafčíková at Masaryk University <500025@mail.muni.cz>
M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory),  N. Werner  (Masaryk U.), M. Ohno (Hiroshima U.),  L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (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 long duration GRB 230518B (Fermi/GBM detection: trigger no. 706068974 initially classified as a GRB; INTEGRAL/SPI-ACS peak detection at 2023-05-18 02:18:15 UT) was detected by the GRB detector on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/).

The data acquisition was performed by the GRB detector unit no. 1. The detection was confirmed at the peak time 2023-05-18 02:18:17 UTC. The T90 duration measured by VZLUSAT-2 is 138 s and the significance during T90 reaches 33 sigma.

The light curve obtained by VZLUSAT-2 is available here:
https://vzlusat2.konkoly.hu/static/share/GRB230518B_GCN_VZLUSAT2.pdf

The event was re-evaluated by the Fermi/GBM team (J. Wood, GCN Circ. 33821Not found
 
 
) to be likely due to local particles. The Fermi satellite was at the GBM trigger time 2023-05-18 02:16:09.41 UT at longitude = 24.33 deg, latitude = -24.43 deg. The VZLUSAT-2 satellite was at that time at longitude = 109.9 deg, latitude = -28.4 deg. Since this event was detected by three satellites at different locations, we believe this event is of astrophysical origin and possibly a long-duration GRB.

All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/
The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat 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.