General information
EP260605a is a fast X-ray transient detected by Einstein Probe WXT at 2026-06-05T09:31:00 UTC, with an initial WXT position of RA 273.360 deg, Dec -40.392 deg and 3.2 arcmin radius uncertainty. EP-FXT follow-up about 25 hours later found an uncatalogued source within the WXT error circle at RA 273.298 deg, Dec -40.3945 deg with 10 arcsec radius uncertainty.
Wavelength coverage
- X-ray: WXT detected a roughly 500 s transient; FXT later detected an uncatalogued X-ray source within the WXT error circle.
- Optical: COLIBRÍ/DDRAGO imaged in simultaneous r and z bands and found no new source within the FXT error region, with limits r > 21.4 and z > 20.6 AB.
No radio, infrared, ultraviolet, gamma-ray, gravitational-wave, or neutrino observations are mentioned.
Lightcurve and spectrum
- WXT light curve started at 2026-06-05T09:31:00 UTC and the event duration was around 500 s.
- WXT spectrum: absorbed power law with Galactic NH fixed at 1.03 x 10^21 cm^-2, photon index 1.76 (-0.58, +0.61), and unabsorbed 0.5–4 keV flux 4.3 (-1.3, +1.6) x 10^-11 erg/s/cm2.
- FXT observed at 2026-06-06T10:39:36 UTC, about 25 hours after WXT detection, with about 6 ks exposure.
- FXT spectrum: absorbed power law with Galactic NH fixed at 1.03 x 10^21 cm^-2, photon index 3.3 (-0.6, +0.5), and average unabsorbed 0.5–10 keV flux 1.1 (-0.4, +0.9) x 10^-13 erg/s/cm2.
- COLIBRÍ observed from 21.93 to 22.59 hours after trigger and obtained later templates at 6.90 to 6.94 days after trigger; image subtraction yielded no optical source to r > 21.4 and z > 20.6.
Redshift
What’s special vs typical
The event is notable as a fast X-ray transient with an uncatalogued fading X-ray source and no detected optical counterpart in the reported COLIBRÍ limits, but the circulars do not establish a physical class or exceptional multi-messenger association.