Long GRB 260310A at z=0.153 with associated supernova and late-time rebrightening

AI Summary

Fermi GBM detected GRB 260310A on 2026-03-10 with T90=86s, Ep=175 keV, and Eiso=9.8×10⁵⁰ erg, classified as a long burst. The optical counterpart AT2026fgk at z=0.153 showed initial power-law decay (α≈-1.2) followed by a break at ~8 days and subsequent X-ray rebrightening with α=2.9±0.5. Spectroscopy confirmed an associated Type Ic-BL supernova with peak brightness ~21.8 mag at 21 days post-trigger. Multi-wavelength observations spanning radio to X-rays tracked the evolving afterglow, with the source located ~13.5 kpc from its host galaxy, suggesting possible merger progenitor.