TITLE: GCN CIRCULAR NUMBER: 39042 SUBJECT: GRB 241223A: cubesat Avion detection DATE: 25/01/27 08:52:00 GMT FROM: Andrey Bogomolov at Moscow State University aabboogg@srd.sinp.msu.ru

A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev on behalf of the MSU “Sozvezdie-270” team, report:

At 2024-12-23 ~12:08:45 UT the long-duration GRB 241223A (Fermi GBM detection: GCN #38650; GRBAlpha detection: GCN #38678) was detected by the DeCoR-1 and DeCoR-3 instruments on the cubesat Avion of the Moscow University project “Constellation-270” [1]. Total amount of photons detected by Avion is 620 (DeCoR-1, energy band 40-500 keV) and ~1540 (DeCoR-3, >30 keV), it corresponds to a fluence of ~7*10^(-6) erg/cm^2 in the range 30-500 keV. LC in the energy range of 30-500 keV has two main episodes with a maximum flux of ~1.6 phot/(cm^2*s) in the 1st peak with a duration of ~11 s, and ~11.7 phot/(cm^2*s) in the 2nd peak with a duration of ~12 s.

А total duration (T90) of the burst is ~31 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB20241223A_Acion_Deco... Parameters of GRB 241223A as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en Avion is one of 5 cubesats of the Moscow University project “Constellation-270” [1] launched on 2023 June 27. The payload of Avion is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV, the time resolution is 0.5s. [1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21 [2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282

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