TITLE: GCN CIRCULAR NUMBER: 30945 SUBJECT: GRB 211018A: Detection by GRBAlpha DATE: 21/10/19 12:05:37 GMT FROM: Masanori Ohno at Hiroshima U <ohno@astro.hiroshima-u.ac.jp> M. Ohno (Eotvos U./Konkoly Observatory/Hiroshima U.), J. Ripa (Masaryk 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. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.) -- the GRBAlpha collaboration. The bright/long duration GRB 211018A (Fermi-GBM detection trigger 656288898/211018936, Fermi-LAT detection; Arimoto et al., GCN Circ. 30943) was detected by the GRBAlpha 1U CubeSat (Pal et al. Proc. SPIE 2020). The light curve shows a very long multiple-peaked structure with a duration of about 168 s (T90 = 140 s). At 22:29:34 UTC, our detection reached a SNR ~ 46. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB211018A_GCN.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.