GCN Circular 34835

M. Kerr, C.C. Cheung, J. E. Grove, R. Woolf (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge (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 231015A, which was also detected by AstroSat and Konus-Wind (GCN 34832
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). AstroSat CZTI detected multiple peaks of emission with the strongest peak at 2023-10-15 23:49:53.50 UTC.

Using an adaptive window with a resolution of 32-ms, the onset for the multi-peaked emission reported by AstroSat is determined to be 2023-10-15 23:49:21.128 with a duration of 36.9 s and a total significance of about 95.4 sigma. The light curve comprises two primary peaks separated by about 15 s.

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=0.1 and a cutoff energy ("Epeak") of 292 keV.  The modeled 10-10000 keV fluence is 3.4e-05 erg/cm^2.

Additional analysis of Glowbug data revealed an earlier component to the two main emission peaks. Using an adaptive window with a resolution of 32-ms, the burst onset of this earlier emission is determined to be 2023-10-15 23:47:03.912 with a duration of 10.3 s and a total significance of about 13.4 sigma.  The light curve comprises a single broad peak.

Using a standard power-law function with an exponential high-energy cutoff [3] to model the emission in the earlier component over this duration results in a photon index dN/dE~E^x of x=2.0 and a cutoff energy ("Epeak") of 193 keV.  The modeled 10-10000 keV fluence is 8.9e-07 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
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[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Goldstein, A. et al. 2020, ApJ 895, 40, arXiv :1909.03006