GRB 260511B

General information

GRB 260511B triggered on 2026-05-11 11:00:31–11:00:32 UT by Fermi/GBM and SVOM/ECLAIRs, and is a long-duration burst (T90 ~ 41–54 s depending on instrument/band). A well-localized, uncatalogued fading X-ray and optical counterpart was reported by SVOM instruments and widely confirmed by ground-based follow-up.

Wavelength coverage

• Gamma-ray/hard X-ray: Fermi/GBM prompt emission with Band fit and fluence; Konus-Wind prompt emission up to ~6 MeV with spectral fits and fluence; AstroSat/CZTI detection; NuSTAR shields detection; SVOM/ECLAIRs and SVOM/GRM triggers.
• X-ray: SVOM/MXT uncatalogued source; EP-FXT fading X-ray source with absorbed power-law spectrum and flux.
• Optical: Multiple detections and multi-filter photometry (e.g., SVOM/C-GFT, MITSuME, SVOM/VT, GTC, LCO, Maidanak, FRAM, SAO RAS, NOT, others).
• Near-IR: SYSU J-band detections (including time series). Bands with no observations mentioned: Radio, sub-mm/mm, UV.

Lightcurve and spectrum

• Prompt emission: Multiple peaks reported; Fermi/GBM Band parameters Epeak=209±16 keV, alpha=-1.01±0.04, beta=-2.14±0.08 and fluence (10–1000 keV) (2.62±0.04)×10^-5 erg/cm^2; Konus-Wind reports two episodes and spectral fits (CPL/Band) with Ep ~259–273 keV.
• X-ray spectrum (EP-FXT, 0.3–10 keV): absorbed power law with intrinsic NH=3.8(±0.10)×10^21 cm^-2 and photon index Γ=2.10±0.04; average unabsorbed flux 2.07(±0.05)×10^-11 erg s^-1 cm^-2.
• Optical decay: FRAM-ORM reports a power-law temporal decay index alpha=1.39±0.29.

Redshift

Afterglow spectroscopy reports a DLA trough and metal absorption lines at z=2.006±0.001 (GTC/OSIRIS+), consistent with Xinglong/BEFOSC absorption at 2.006 and OHP/MISTRAL z=2.007±0.001; an intervening absorber is reported near z1.435–1.437.

What’s special vs typical