EP260214b

General information

EP260214b is a fast X-ray transient detected by Einstein Probe/WXT at 2026-02-14 22:04:12 UTC (T0=22:03:34) with ~50 s duration, followed by EP/FXT localization of an uncatalogued X-ray source and identification of an optical counterpart.

Wavelength coverage

• X-ray: EP/WXT detection with spectral fit and flux estimate; EP/FXT follow-up detection with spectrum and flux at ~5.8 hr.
• Optical/NIR: Multiple optical imaging detections and limits (g/r/i/z, VT_B/VT_R, w), plus VLT/X-shooter spectroscopy covering 3000–21000 Å.
• Radio: ATCA 6 GHz non-detection at 17 days and detection (0.04 mJy) at ~34 days. Bands with no observations mentioned: gamma-ray, UV (space-based UV), millimeter/submillimeter, gravitational waves, neutrinos.

Lightcurve and spectrum

• X-ray spectrum (EP/WXT, 0.5–4 keV): absorbed power law with Galactic NH=1.57×10^20 cm^-2 fixed and photon index 0.7±0.4; unabsorbed flux 2.1(-0.5/+0.7)×10^-9 erg s^-1 cm^-2 (average over the transient).
• X-ray follow-up (EP/FXT, 0.5–10 keV at ~5.8 hr): absorbed power law with NH fixed and photon index 2.2(+0.3/-0.3); unabsorbed flux ~2.8(+0.7/-0.5)×10^-13 erg s^-1 cm^-2.
• Optical photometry: r'=20.90±0.04 (2.22 hr); r=21.22±0.13 (3.6 hr); VT_B=21.29±0.08 and VT_R=20.84±0.07 (6.94 hr) with no significant variation reported from 5.81–8.08 hr; later detections include LT g=22.45±0.27, r=22.22±0.33, i=21.75±0.24 (~28.9–29.3 hr) and Mondy R=21.67±0.16 at 1.93455 d; limits include r'>20.9 (18.4 hr), r>22.2 (16.5 hr), and R>22.40 (50.82 hr).
• Radio: ATCA 6 GHz 3σ upper limit ~50 uJy at ~17 days; detection of ~0.04 mJy at ~34 days.

Redshift

• z=1.208 measured with VLT/X-shooter from multiple absorption lines (Al II, Fe II, Mg II), with host-galaxy emission lines consistent with z=1.207.

What’s special vs typical

• Secure, rapid spectroscopic redshift with both absorption and host emission features reported, and a late-time 6 GHz radio detection following an earlier deep non-detection.