GCN Circular 45797
GRB 261003A: Fermi GBM Final Real-time Localization
From: Fermi GBM Team at MSFC/Fermi-GBM
Issued: 2026-10-03 01:29 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 SHORT GRB
At 01:18:35 UT on 3 Oct 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 261003A (trigger 812683120.140818 / 261003055).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 306.5, Dec = 45.7 (J2000 degrees, equivalent to J2000 20h 26m, 45d 42'), with a statistical uncertainty of 20.7 degrees.
The angle from the Fermi LAT boresight is 87.0 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/bn261003055/quicklook/glg_healpix_all_bn261003055.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
On 3 October 2026, NASA's Fermi space telescope picked up a brief flash of gamma rays (the most energetic form of light) from a spot in the northern sky, in the direction of the constellation Cygnus. The flash looks like a short gamma-ray burst, a type that usually lasts under about two seconds and is often linked to the merger of two dense dead stars. Glowbug, a gamma-ray detector on the International Space Station, also saw it, as a single peak lasting about a tenth of a second. Fermi could only place it within a large patch of sky, roughly 20 degrees across, and a Russian-led robotic telescope network searched part of that area about 77 minutes later and found no new visible source down to a certain faintness. No distance or afterglow (fading light from the explosion) has been reported so far.
How unusual is it? Short bursts are a regular catch for Fermi, and this one has only a rough location, no afterglow and no measured distance. It would become more interesting if a faint afterglow or a host galaxy were found, or if a gravitational-wave signal were tied to it.
Written by an AI model (claude-sonnet-5-5) from the official reports in this thread; last updated . It may contain mistakes: the reports themselves are the authority.
GRB 261003A