General information
EP260306a is a fast X-ray transient detected by Einstein Probe/WXT (trigger 01709258759) with EP/FXT follow-up identifying an uncatalogued X-ray source consistent with a fading optical counterpart.
Wavelength coverage
- X-ray: EP/WXT detection and refined temporal/spectral analysis; EP/FXT localization and spectrum/flux reported.
- Optical: Las Cumbres discovery photometry; COLIBRÍ r/z detections and fading; SVOM/VT detections in VT_B and VT_R; Gemini-N/GMOS-N spectroscopy; Mondy R-band non-detections at later times.
No observations mentioned in: gamma-ray, ultraviolet, infrared, radio, millimeter.
Lightcurve and spectrum
- X-ray temporal: event start T0=2026-03-06 01:28:20 UTC; duration ~60 s (WXT).
- X-ray spectrum (WXT, 0.5–4 keV): absorbed power law with photon index 4.01 (-2.04/+3.04) and additional absorption; unabsorbed flux reported with very large uncertainties.
- X-ray spectrum (FXT, 0.5–10 keV): absorbed power law with photon index 2.36 (-0.38/+0.41) and additional absorption; unabsorbed flux 1.37(-0.16/+0.20)×10^-12 erg s^-1 cm^-2.
- Optical evolution: compared to earlier report, optical counterpart faded; temporal decay index alpha ≈ 1.
- Optical/NIR spectrum: Gemini-N/GMOS-N detects continuum down to ~7020 Å with a break; multiple absorption features are reported.
Redshift
Gemini-N/GMOS-N spectroscopy establishes z = 4.773 from the Lyman-forest/damping-wing break and multiple absorption features at a common redshift.
What’s special vs typical
Secure high-redshift (z=4.773) spectroscopic identification for an EP fast X-ray transient with a rapidly fading, very red optical counterpart.