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GCN Circular 35879

GRB 231028C: Glowbug gamma-ray confirmation of a prior burst
2024-03-05T21:53:20Z (4 months ago)
C.C. Cheung at Naval Research Lab <>
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C.C. Cheung, M. Kerr, J.E. Grove, R. Woolf (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 231028C, which was also detected by Konus/Wind (Trigger time 12:31:37.779 UT).  This was previously identified in Glowbug data as a candidate GRB, and we report it here as confirmation of the independent Konus/Wind trigger.
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2023-10-28 12:31:37.104 with a duration of 4.1 s and a total significance of about 12.7 sigma.  The light curve comprises a single peak.
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=0.6 and a cutoff energy ("Epeak") of 303 keV.  The modeled 10-10000 keV fluence is 2.1e-06 erg/cm^2.
The best-fit localization was RA, Decl. (J2000, deg) = 125.5,-45.5 with a radius of 22.3 deg (95% confidence), with a highly uncertain systematic uncertainty.
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.
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