EP260227a

General information

EP260227a is an Einstein Probe/WXT-triggered X-ray transient (trigger time 2026-02-27 20:12:29 UTC; refined T0=20:07:52 UTC; duration ~250 s) with an EP/FXT uncatalogued X-ray source and a widely reported fading optical counterpart.

Wavelength coverage

• X-ray: EP/WXT detection and spectral fit; EP/FXT counterpart detection and spectral fit.
• Optical/UV: u/g/r/i/z, R, w, KG5, VT_B/VT_R photometry and limits from multiple facilities.
• Near-IR: J-band observations mentioned (no magnitude reported in extracted facts). No observations were mentioned in gamma-ray, radio, millimeter/sub-mm, or neutrinos.

Lightcurve and spectrum

• X-ray (WXT, 0.5–4 keV): absorbed power-law with fixed Galactic NH=9.3e20 cm^-2, photon index 0.8 (-0.6/+0.6), average unabsorbed flux 4.1 (-1.3/+1.7)e-10 erg s^-1 cm^-2.
• X-ray (FXT, 0.5–10 keV): absorbed power-law with NH=2.2 (-0.2/+0.2)e21 cm^-2, photon index 1.47 (-0.04/+0.04), unabsorbed flux 8.3 (-0.1/+0.1)e-10 erg s^-1 cm^-2.
• Optical photometry shows fading: e.g., r=20.18±0.04 at 2.47 hr; r~20.28±0.09 to 21.08±0.10 between 0.954 and 1.011 d (LCO w calibrated to r); r=22.92±0.06 at ~25.1 hr (DOT R); r=22.82±0.28 at 36.1 hr (LCO); r=24.80±0.33 at 81.9 hr (Gemini; noted as possibly host-dominated).
• Optical spectroscopy (GTC/OSIRIS): Lyman-forest break (~4500 Å) and narrow absorption features (Si II, C II, C IV) reported.

Redshift

• z = 2.714 measured from GTC/OSIRIS spectroscopy via Lyman-forest break and narrow absorption lines.

What’s special vs typical

• A spectroscopic redshift at z=2.714 was obtained within hours alongside extensive multi-telescope optical follow-up and an EP/FXT localized X-ray counterpart.