GCN Circular 45811
GRB 261005A: Fermi GBM Final Real-time Localization
From: Fermi GBM Team at MSFC/Fermi-GBM
Issued: 2026-10-05 20:29 UTC
Why this event is posted: every one of the gamma-ray bursts is posted.
The Fermi GBM team reports the detection of a likely LONG GRB
At 20:19:03 UT on 5 Oct 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 261005A (trigger 812924348.321234 / 261005847).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 339.9, Dec = 5.5 (J2000 degrees, equivalent to J2000 22h 39m, 5d 30'), with a statistical uncertainty of 5.8 degrees.
The angle from the Fermi LAT boresight is 64.0 degrees.
The skymap can be found here:
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn261005847/quicklook/glg_healpix_all_bn261005847.fit
The GBM light curve can be found here:
Every one of the gamma-ray bursts GCN reports is posted here.
Relayed automatically from NASA's General Coordinates Network.
In plain words Routine
A burst of gamma rays, the most energetic form of light, reached Earth on 5 October 2026 and was recorded by three separate space telescopes: Fermi, Glowbug (an experiment on the International Space Station) and China's GECAM-B. Fermi places it in the constellation region around 22h 39m right ascension and +5.5 degrees declination, but only roughly, with an uncertainty of about 6 degrees. Fermi classed it as a likely long burst, the kind usually linked to the collapse of a massive star. Glowbug measured a single peak lasting about 5 seconds, and GECAM-B estimated about 9 seconds with a large margin of error. No distance, afterglow or visible-light counterpart has been reported so far.
How unusual is it? This is a typical single-pulse long gamma-ray burst, of a kind Fermi and Swift see a few hundred times a year, with only a rough location and no distance or afterglow reported. A measured distance or a detected afterglow would make it notable.
Written by an AI model (claude-sonnet-5-5) from the official reports in this thread, and rewritten as new reports arrived (version 2); last updated . It may contain mistakes: the reports themselves are the authority.
GRB 261005A