TITLE: GCN CIRCULAR NUMBER: 42506 SUBJECT: GRB 251028A: Glowbug gamma-ray detection DATE: 25/10/28 17:54:20 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 251028A, which was also detected by Fermi/GBM (GCN 42497, 42499) and MAXI/GSC (GCN 42498). Using an adaptive window with a resolution of 32-ms, and taking the GBM-reported T0 (2025-10-28 03:26:31 UT), the burst onset is determined to be T0+22.48s with a duration of 2.0 s and a total significance of about 7.5 sigma. The single peak observed by Glowbug corresponds to the maximum in the Fermi/GBM light curve (GCN 42497). Additional lower-level emission from ~T0+5s to T0+20s may be present in the Glowbug light curve at low significance. 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/42506. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...