GRB 251130A

General information

GRB 251130A is associated with the Einstein Probe fast X-ray transient EP251130a, with X-ray counterparts reported by EP/FXT and Swift/XRT and a well-observed optical/NIR afterglow. Spectroscopy with GTC/OSIRIS+ measured a high redshift of z=4.035 and contemporaneous photometry reported a rebrightening followed by rapid fading.

Wavelength coverage

• Gamma-rays: Fermi/GBM trigger and real-time localization reported.
• X-ray: Einstein Probe WXT trigger and refined analysis; EP/FXT follow-up detection; Swift/XRT counterpart detection and fluxes.
• Optical: Extensive multi-telescope detections (r/i/z/R and clear) including rapid-response and multi-epoch monitoring.
• Near-infrared: J-band detection reported at ~1.3 days. No reports in: UV, radio, mm/sub-mm, GeV/TeV observations.

Lightcurve and spectrum

• X-ray duration: EP/WXT event lasted ~230 s (0.5–4 keV).
• X-ray spectrum (EP/WXT): absorbed power law with photon index 1.54 (-0.63/+0.70); unabsorbed avg flux 2.46 (-0.77/+1.06) x 10^-10 erg/s/cm^2 (0.5–4 keV).
• X-ray spectrum (EP/FXT): absorbed power law with photon index 2.12 (-0.32/+0.34); unabsorbed avg flux 3.32 (-0.31/+0.32) x 10^-12 erg/s/cm^2 (0.5–10 keV).
• X-ray flux (Swift/XRT): mean flux (2.21 [+0.25, -0.24])e-12 erg cm^-2 s^-1 (0.3–10 keV), with peak flux (5.0 +/- 1.1)e-12 erg cm^-2 s^-1 reported.
• Optical temporal behavior: early clear-band decay index 0.46 between ~16 and 91 minutes, followed by a reported rebrightening at ~0.89 days; i-band rebrightening by ~1 mag in ~10 hr; later power-law decay indices reported around ~2.2, and steepening/slope changes up to ~4 at ~0.9–1.4 days (observer frame).

Redshift

• z = 4.035 from GTC/OSIRIS+ spectroscopy, based on a broad trough near 6120 Å interpreted as a DLA plus multiple metal absorption lines at a common redshift.

What’s special vs typical

• Secure, high redshift (z=4.035) measured from spectroscopy.
• Strong optical rebrightening (~1 mag over ~10 hr) followed by very steep late-time fading reported across multiple optical datasets.