TITLE: GCN CIRCULAR NUMBER: 41891 SUBJECT: GRB 250919A: Glowbug gamma-ray detection DATE: 25/09/19 18:58:32 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 250919A, which was also detected by Fermi/GBM (GCN 41874, 41881, 41890), SVOM/GRM (GCN 41882), and NuSTAR (GCN 41888), and associated with the Einstein Probe transient EP250919a (GCN 41879). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-09-19 00:28:56.288 with a duration of 32.1 s and a total significance of about 14.5 sigma. The burst originated toward the Nadir side of Glowbug and was detected despite passing through the passive material from the H9 pallet and internal passive material/shielding within Glowbug. The observed light curve comprises two primary peaks at ~T0+24s and ~T0+28s. Note that data from ~T0+30s to +38s 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 recently 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/41891. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...