GRB 230918A
GCN Circular 34726
Subject
GRB 230918A: Fermi GBM Final Real-time Localization
Date
2023-09-18T10:03:09Z (2 years ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely SHORT GRB
At 09:52:36 UT on 18 Sep 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230918A (trigger 716723561.504536 / 230918412).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 222.5, Dec = -11.6 (J2000 degrees, equivalent to J2000 14h 50m, -11d 35'), with a statistical uncertainty of 17.1 degrees.
The angle from the Fermi LAT boresight is 63.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230918412/quicklook/glg_skymap_all_bn230918412.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230918412/quicklook/glg_healpix_all_bn230918412.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230918412/quicklook/glg_lc_medres34_bn230918412.gif
GCN Circular 34733
Subject
GRB 230918A (short): Glowbug gamma-ray detection
Date
2023-09-18T22:20:21Z (2 years ago)
From
matthew.kerr@gmail.com
Via
Web form
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 the short GRB 230918A, which was also detected by Fermi/GBM (GCN 34726).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2023-09-18 09:52:35.360 with a duration of 0.128 s and a total significance of about 12.9 sigma.
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=0.7 and a cutoff energy ("Epeak") of 417 keV. The modeled 10-10000 keV fluence is 1.7e-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
[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.