GRB 251122A

General information

GRB 251122A (also EP251122a) was detected by SVOM/ECLAIRs and independently triggered Einstein Probe/WXT, with an X-ray counterpart localized by EP/FXT and an optical afterglow reported by multiple telescopes. A host galaxy spectrum taken with VLT/X-shooter yields a likely redshift of z = 1.765.

Wavelength coverage

• Gamma-ray / hard X-ray: SVOM/ECLAIRs detection in the 5–20 keV band.
• Soft X-ray: EP/WXT (0.5–4 keV) and EP/FXT (0.5–10 keV) detections and spectral fits; SVOM/MXT X-ray counterpart reported.
• Optical: Multiple detections/limits in r/R/i/VT_R bands within hours to ~0.3–0.4 days after trigger.
• Near-IR: J-band observations reported (upper limit). No observations were mentioned in radio, mm/sub-mm, UV, GeV/TeV gamma rays, or gravitational waves/neutrinos.

Lightcurve and spectrum

• Duration: EP/WXT reports the event lasted ~10 s with a single pulse.
• X-ray temporal structure: EP/FXT light curve shows two pulses lasting ~400 s.
• X-ray spectrum (EP/WXT, 0.5–4 keV): absorbed power law with photon index Γ = 1.26 (-0.58/+0.59); average unabsorbed flux 2.07 (-0.67/+0.77)×10^-9 erg s^-1 cm^-2.
• X-ray spectrum (EP/FXT, 0.5–10 keV): absorbed power law with photon index Γ = 1.74 (-0.05/+0.04); average unabsorbed flux 7.66 (-0.30/+0.33)×10^-11 erg s^-1 cm^-2.
• Optical photometry examples: VT_R 21.82 at 7.65 min and ~21.96 at 88.3 min; i ~21.89 at ~1.85 hr; R ~22.7 at ~33 min; r23.1 at 0.31 hr; R~22.37 at ~2.15 hr.

Redshift

• Spectroscopic redshift: z = 1.765 from VLT/X-shooter, based on a clear emission line at 18140 Å interpreted as Hα; alternative identifications ([O II] at z=3.87; [O III] at z=2.62) were argued against.

What’s special vs typical

• EP-discovered fast X-ray transient with a reported association to a long GRB and detailed early X-ray spectral/temporal characterization.
• Secure late-time spectroscopy provides a likely host redshift (z = 1.765), enabling physical interpretation beyond basic afterglow detection.