TITLE: GCN CIRCULAR NUMBER: 43612 SUBJECT: GRB 260121A: 239Alferov CubeSat detection DATE: 26/02/03 16:12:40 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru> D. Svinkin (Ioffe), D. Frederiks (Ioffe), D. Kapshtan (Geoscan), M. Orlov (Geoscan), V. Bazunova (Geoscan), E. Shchepin (Geoscan), E. Meltsov (Geoscan), K. Starikov (Geoscan, SPbSU), A. Khogoev (Geoscan), A. Razdobarin (SPbAU), and D. Dolmatov (SPbSU), on behalf of the 239Alferov team, report: The long-duration GRB 260121A (IPN triangulation: Kozyrev et al., GCN 43564; Konus-Wind detection: Ridnaia et al., GCN 43611) was detected by 239Alferov 3U CubeSat at about 8552 s (02:22:32) UT. The burst light curve, as measured by 239Alferov detector, shows a single pulse with a duration of ~13 s. The emission is seen up to above ~1 MeV. The light curve recorded by 239Alferov is available at: http://www.ioffe.ru/LEA/GRBs/GRB260121_T08549/239Alferov/ 239Alferov is an educational 3U CubeSat mission at SSO combining amateur radio and space research objectives. The gamma-ray detector onboard 239Alferov contains a 64x72x15 mm NaI(Tl) scintillator read out by a SiPM array and covers the energy range from ~20 keV to ~1000 keV. The spacecraft is now at a commissioning stage, with scientific observations started in December 2025. Currently, the instrument records count rates in five energy bands: ~20-50 keV, ~50-100 keV, ~100-500 keV, 500-1000 keV, and > 1000 keV, with 1 s temporal resolution. The surveys span a couple of days with about a day-long analysis and maintenance intervals between the observations. The ground segment of the mission utilizes the SONIKS open ground station network. View this GCN Circular online at https://gcn.nasa.gov/circulars/43612. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...