EP260518a

General information

EP260518a is a sub-threshold soft X-ray transient detected by Einstein Probe (WXT) and associated with the optical transient AT2026ndp, with subsequent EP/FXT X-ray follow-up detecting an uncatalogued source near the optical position.

Wavelength coverage

• X-ray: EP/WXT detection (0.5–4 keV flux ~2.5×10^-11 erg cm^-2 s^-1) and EP/FXT detection with spectral fit and 0.3–10 keV flux ~4.6×10^-13 erg cm^-2 s^-1.
• Optical: ATLAS discovery (c=18.73±0.10) and LCO imaging (r=20.78±0.04, z=20.31±0.10), plus Gemini-S/GMOS spectroscopy. No observations were mentioned in gamma-ray, UV, IR, radio, or mm bands.

Lightcurve and spectrum

Redshift

Gemini-S/GMOS absorption features are reported at z=2.28; the authors note this is formally a lower limit (no fine-structure lines or Lyα absorption), and infer z<2.75 from the lack of a Lyα break, concluding z=2.28 is likely.

What’s special vs typical

A likely spectroscopic absorption-line redshift (z=2.28) is reported, and the nearby Legacy Survey point source placed on the slit is identified as a Galactic M-dwarf (helping disambiguate the blend).