Fermi GBM detected a long GRB on 2026-09-26; classified as likely AGN with 88% confidence

AI Summary

Fermi GBM triggered on a long gamma-ray burst (GRB 260926A) at 2026-09-26 16:20:14 UT with trigger ID 812132419. The on-ground localization places the source at RA=20.2°, Dec=65.3° (J2000) with a statistical uncertainty of 5.8°. However, the flight-based classification algorithm assigns 88% probability to AGN rather than a true GRB, with only 6% probability for a generic transient, suggesting this may be a misclassified AGN flare. MASTER-Tunka robotic telescope observations began 94 seconds post-notice and detected no optical transient down to magnitude 18.5.

Measurements

Notices (1)

Fermi GBM — GRB · Sat, 26 Sep 2026 16:20:14 GMT

GCN Circulars (2)

GCN-45763 — GRB 260926A · Sat, 26 Sep 2026 17:31:32 GMT
The MASTER-Tunka robotic telescope in Russia began observing the error box of Fermi GRB 260926A 94 seconds after the notice time, with an upper limit magnitude of 18.5. The observations were conducted at a zenith distance of 23 degrees and a sun altitude of -38.9 degrees, with no optical transient detected.

GCN-45761 — GRB 260926A · Sat, 26 Sep 2026 16:30:40 GMT
The Fermi Gamma-ray Burst Monitor (GBM) detected a likely long Gamma-Ray Burst (GRB) on 26 September 2026 at 16:20:14 UT, designated GRB 260926A, with a statistical uncertainty of 5.8 degrees and an angle of 81.0 degrees from the Fermi LAT boresight. The event's location is RA = 20.2, Dec = 65.3 (J2000).