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GCN Circular 35845

Subject
GRB 240225A (short): Glowbug gamma-ray detection
Date
2024-03-02T14:34:30Z (2 months ago)
From
C.C. Cheung at Naval Research Lab <Teddy.Cheung@nrl.navy.mil>
Via
Web form
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 the short GRB 240225A, which was also detected by Swift/BAT (GCN 35793) and INTEGRAL/SPI-ACS (Trigger 10589).
 
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2024-02-25 04:20:17.488 with a duration of 2.05 s and a total significance of about 25.4 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=0.04 and a cutoff energy ("Epeak") of 670 keV.  The modeled 10-10000 keV fluence is 1.6e-06 erg/cm^2.
 
The best-fit localization is RA, Decl. (J2000, deg) = 82.5,-37.9 with a radius of 14.3 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
 
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