TITLE: GCN CIRCULAR NUMBER: 44801 SUBJECT: GRB 260601B/EP260601a: Glowbug gamma-ray detection DATE: 26/06/03 12:57:03 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 260601B, which was detected initially by Einstein Probe as EP260601a (GCN 44766). The GRB was also detected by GECAM-B (GCN 44767, 44768), NuSTAR (GCN 44771), CALET (GCN 44773), and Insight-HXMT (GCN 44785). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-06-01 19:12:50.296 with a duration of 39.7 s and a total significance of about 17.3 sigma. The light curve comprises an initial 2.05-s duration burst followed by a long-duration episode from ~T0+16.4s to +39.7s. Note that data from ~T0-2s to +1s, ~T0+5s to +10s, and ~T0+37s to +40s 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/44801. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...