Discovery of the optical and radio counterpart to the fast X-ray transient EP240315a

Understand

Fast X-ray Transients (FXTs) are extragalactic bursts of soft X-rays first identified >10 years ago.

• Since then, nearly 40 events have been discovered, although almost all of these have been recovered from archival Chandra and XMM-Newton data.
• To date, optical sky surveys and follow-up searches have not revealed any multi-wavelength counterparts.
• The Einstein Probe, launched in January 2024, has started surveying the sky in the soft X-ray regime (0.5-4 keV) and will rapidly increase the sample of FXTs discovered in real time.