GRB 260531B
GCN Circular 44762
Subject
GRB 260531B: Glowbug gamma-ray detection
Date
2026-06-01T22:31:42Z (3 days 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 [1,2,3], operating on the International Space Station, reports the detection of GRB 260531B, which was also detected by Fermi/GBM (GCN 44747) and GECAM-B (GCN 44754).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-31 13:57:58.840 with a duration of 8.2 s and a total significance of about 31.6 sigma. The light curve comprises a complex multi-peaked structure.
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 and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12.
[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] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108
Distribution Statement A: Approved for public release. Distribution is unlimited.
GCN Circular 44754
Subject
GRB 260531B: GECAM-B observation
Date
2026-06-01T10:08:05Z (4 days ago)
From
Xinghao Luo at IHEP <2952704891@qq.com>
Via
Web form
Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered in-flight by GRB 260531B, at 2026-05-31T13:58:00.050 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44747).
According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 12 +5/-3 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb260531B.png
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
GCN Circular 44747
Subject
GRB 260531B: Fermi GBM Final Real-time Localization
Date
2026-05-31T14:08:37Z (5 days 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 LONG GRB
At 13:57:59 UT on 31 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260531B (trigger 801928684.989378 / 260531582).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 282.6, Dec = 6.4 (J2000 degrees, equivalent to J2000 18h 50m, 6d 24'), with a statistical uncertainty of 2.2 degrees.
The angle from the Fermi LAT boresight is 48.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260531582/quicklook/glg_skymap_all_bn260531582.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260531582/quicklook/glg_healpix_all_bn260531582.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260531582/quicklook/glg_lc_medres34_bn260531582.gif