TITLE: GCN CIRCULAR NUMBER: 45233 SUBJECT: GRB 260727A: Glowbug gamma-ray detection DATE: 26/07/27 22:08:29 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 260727A, which was also detected by SVOM (GCN 45220) and AstroSat (GCN 45225).  Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-07-27 00:21:57.592 with a duration of 22.5 s and a total significance of about 24.2 sigma.  The emission seen by Glowbug corresponds to the brightest portion of the burst seen in the AstroSat light curve, and is a subset of the full emission episode observed by SVOM. 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/45233. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...