TITLE: GCN CIRCULAR NUMBER: 42407 SUBJECT: GRB 251023B: Glowbug gamma-ray detection DATE: 25/10/23 19:43:30 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 251023B, which was also detected by MAXI (as MAXI J0451+122; GCN 42392) and CALET (GCN 42402), and possibly associated with the Einstein Probe/WXT-detected source EP#01709247298 (GCN 42401). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-23 08:48:53.664 with a duration of 7.9 s and a total significance of about 7.0 sigma. The onset measured by Glowbug is 9.4 s prior to the MAXI-reported T0. The Glowbug light curve is dominated by a single peak corresponding to the maximum in the CALET light curve (GCN 42402). 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/42407. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...