GRB 240128A: Glowbug gamma-ray detection

The Glowbug gamma-ray telescope [1,2], operating on the International Space Station, reports the detection of GRB 240128A, which was also detected by MAXI/GSC (GCN 35646), CALET/CGBM (GCN 35647), GRBAlpha (GCN 35649), and INTEGRAL/SPI-ACS (Trigger 10493). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2024-01-28 15:13:35.064 with a duration of 18.4 s and a total significance of about 44.8 sigma. The light curve comprises a multi-peaked structure similar to that observed by CALET/CGBM (GCN 35647). Using a standard power-law function with an exponential high-energy cutoff [3] to model the emission over this duration results in a photon index dN/dE~E^x of x=1.9 and a cutoff energy ("Epeak") of 176 keV. The modeled 10-10000 keV fluence is 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.