TITLE: GCN CIRCULAR NUMBER: 43856 SUBJECT: GRB 260225D: Glowbug gamma-ray detection of a likely short burst DATE: 26/02/26 20:53:48 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung@nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260225D, which was also detected by Konus-Wind (Trig_Time 19:51:32.84) and SVOM/GRM (sb26022503). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-02-25 19:51:28.768 with a duration of 1.98 s and a total significance of about 62 sigma.  The light curve comprises two primary peaks at ~T0+0.2s and +1.6s. The best-fit localization is RA, Dec. (J2000, deg) = 94.7, 13.8 with a radius of 7.0 deg (95% confidence), with a highly uncertain systematic uncertainty. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC.  It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release.  Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/43856. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...