TITLE:   GCN CIRCULAR
NUMBER:  42120
SUBJECT: GRB 250902A: MSU cubesats detection
DATE:    25/10/06 08:17:18 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 2025-09-02 ~01:30:00 UT the long-duration GRB 250320B (Fermi GBM detection: GCN #41648; SVOM detection: GCN #41653, GECAM-B detection: GCN #41687, VZLUSAT-2 detection: GCN #41701, CALET detection: GCN #41703) was detected on the cubesats Avion (the instruments DeCoR-1 and DeCoR-3) and Altair (DeCoR-2) of the Moscow University project “Sozvezdie-270” [1].
  
Total amount of photons detected by Avion is 644 (DeCoR-1, energy band 40-500 keV) and 583 (DeCoR-3, energy band 30-500 keV), it corresponds to a fluence of ~5*10^(-6) erg/cm^2 in the range 30-500 keV (DeCoR-3) and ~3*10^(-6) erg/cm^2 in the range 40-500 keV (DeCoR-1)

LC in the energy range of 30-500 keV consists of a single episode of 7 s duration with a maximum flux of ~15 phot/(cm^2*s), supplemented at the beginning by an additional short increase (less than 2 s).

А total duration (T90) of the burst is ~7 s.

The light curve obtained by Avion is available here:
https://swx.sinp.msu.ru/models/grb_cat/data/pictures/avion_d3_250902.png

Parameters of GRB 250902A 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 and Altair are the cubesats of the Moscow University project “Constellation-270” [1] launched on 2023 June 27 (Avion) and on 2024 November 5 (Altair). The payload of both cubesats is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV (Avion) and >50 keV (Altair), the time resolution is 0.5s (Avion) and 1 s (Altair).

[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