TITLE: GCN CIRCULAR NUMBER: 43824 SUBJECT: GRB 260223A: Glowbug gamma-ray detection DATE: 26/02/25 05:26:59 GMT FROM: Richard S. Woolf at US Naval Research Laboratory <richard.s.woolf.civ@us.navy.mil> R. Woolf, C.C. Cheung, 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 260223A, which was also detected by Fermi GBM (GCN 43808) and SVOM/GRM (GCN 43815). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-02-23 04:11:09.520 with a duration of 20.5 s and a total significance of about 48.4 sigma. Following the initial event onset, the light curve comprises two main peaks at ~T0+11s and +18s. Note that data from ~T0+15s to T0+17s suffered from deadtime in various detectors.  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/43824. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...