GRB 230521A

The Fermi GBM team reports the detection of a likely SHORT GRB

At 05:03:23 UT on 21 May 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230521A (trigger 706338208.733194 / 230521211).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 37.0, Dec = 7.6 (J2000 degrees, equivalent to J2000 02h 28m, 7d 35'), with a statistical uncertainty of 7.8 degrees.

The angle from the Fermi LAT boresight is 54.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230521211/quicklook/glg_skymap_all_bn230521211.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230521211/quicklook/glg_healpix_all_bn230521211.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230521211/quicklook/glg_lc_medres34_bn230521211.gif

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 GRB detectors on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/) detected a likely long-duration GRB 230521A. The event was triggered by Konus/Wind at 2023-05-21 18:52:04.019 UT and also observed by INTEGRAL/SPI-ACS at 2023-05-21 18:52:13 UT. The GOES-P X-ray flux does not show any increase at the time of this detection, therefore, it is unlikely to be a solar flare.

The data acquisition was performed by the GRB detector units no. 0 and no. 1. The detection was confirmed at the peak time 2023-05-21 18:52:10 UTC. The T90 duration is 45 s (46 s) and the significance during T90 reaches 11 sigma (16 sigma) for detector unit no. 0 (no. 1).

The light curve obtained by VZLUSAT-2 is available here:
https://vzlusat2.konkoly.hu/static/share/GRB230521A_GCN_VZLUSAT2.pdf

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.