TITLE:   GCN CIRCULAR
NUMBER:  30624
SUBJECT: GRB 210807A: Detection by GRBAlpha
DATE:    21/08/10 14:37:22 GMT
FROM:    Masanori Ohno at Hiroshima University  <ohno@astro.hiroshima-u.ac.jp>

J. Ripa (Masaryk U.), M. Ohno (Eotvos U./Hiroshima U.), H. Takahashi
(Hiroshima U.),
A. Pal, L. Meszaros, B. Csak (Konkoly Observatory), N. Werner, M. Topinka,
F. Munz,
F. Hroch (Masaryk U.), T. Urbanec, M. Kasal,  A. Povalac (Brno U. of
Technology),
J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda
(Needronix s.r.o),
M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi
(Wigner Research Center/Eotvos U.),
Yuusuke Uchida, Helen Poon, H. Matake, N. Uchida (Hiroshima U.), T. Enoto
(Kyoto U.), Zs. Frei (Eotvos U.),
Y. Fukazawa, K. Hirose (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.) -- the GRBAlpha
collaboration.

The long duration GRB 210807A (Swift-BAT detection; Lien et al. GCN Circ.
 30600)
was detected by the GRBAlpha 1U CubeSat (Pal et al. Proc. SPIE 2020).
This is the first time that a GRB was observed by a 1U CubeSat dedicated to
gamma-ray burst observations.

The data acquisition started at 10:05:14 UT and the tail part of the prompt
emission, which  consists of multiple peaks,
was observed with a duration of about 80 sec. The 7.3 sigma detection
significance was confirmed at around 10:06:00 UT.

The light curve obtained by GRBAlpha is available here:
https://grbalpha.konkoly.hu/static/share/GRB210807A.pdf

GRBAlpha is a demonstration mission for a future CubeSats constellation
(Werner et al. Proc. SPIE 2018).
The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator
read out by a SiPM array,
covering the energy range from ~50 keV to ~1000 keV.
GRBAlpha was launched on 2021 March 22 from Baikonur. After its
commissioning phase,
the scientific observations are now under way. To increase the duty cycle
and the downlink rate,
the upgrade of the on-board data acquisition software stack is in progress.
The ground segment is also supported by the radio amateur community and it
takes advantage
of the SatNOGS network for increased data downlink volume.