TITLE: GCN CIRCULAR NUMBER: 35848 SUBJECT: GRB 240225B: Glowbug gamma-ray detection DATE: 24/03/03 04:22:32 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], operating on the International Space Station, reports the detection of GRB 240225B, which was also detected by MAXI/GSC (GCN 35796), AstroSat/CZTI (GCN 35798), CALET (GCN 35811), and Konus/Wind (GCN 35835). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2024-02-25 20:11:58.416 with a duration of 38.9 s and a total significance of ~89 sigma. The light curve comprises a multi-peaked structure with two primary peaks at ~T0+3s and ~T0+8s, and a fainter peak at ~T0+34s. Using a standard power-law function with an exponential high-energy cutoff [3] to model the emission in two defined intervals from T0 to T0+22.5s and T0+22.5s to +38.9s resulted respectively in photon indices dN/dE~E^x of x=0.6 and x=0.7, and cutoff energies ("Epeak") of 324 keV and 262 keV. The respective modeled 10-10000 keV fluences are 9.7e-06 erg/cm^2 and 2.0e-06 erg/cm^2. 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. The detector comprises 12 large-area (15 cm x 15 cm) CsI:Tl panels covering the surface of a half cube, and two hexagonal (5-cm diameter, 10-cm length) CLLB scintillators, giving it a large field of view (instantaneous FoV ~2/3 sky) over a wide energy band of 50 keV to >2 MeV. [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] Goldstein, A. et al. 2020, ApJ 895, 40, arXiv :1909.03006 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/35848. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...