Characterizing EP241107a: Multiwavelength observations of an Einstein probe-detected fast X-ray transient

Abstract

Fast X-ray transients (FXTs) represent a new class of highly luminous transients in soft X-rays ( ∼0.3–10 keV) associated with violent astrophysical processes. They manifest as short, singular flashes of X-ray photons with durations lasting from minutes to hours. Their origin remains unclear, and they have been associated with various progenitor mechanisms. The newly launched X-ray survey, Einstein Probe (EP), is revolutionizing this field by enabling the discovery and immediate follow-up of FXTs. Here, we present the multiwavelength observations of EP-discovered FXT EP241107a and the discovery of its radio counterpart. Comparison of the optical and radio observations of EP241107a and its host properties with other extragalactic transients suggests a gamma-ray burst (GRB) origin. Through our afterglow modelling, we infer the GRB jet properties for EP241107a, yielding a jet of the isotropic-equivalent kinetic energy EK, iso ∼ 1051 erg, with a half opening angle θc ≈ 15◦, viewed at an angle of θobs ≈ 9◦. We also evaluate EP241107a in the landscape of both EP-discovered FXTs as well as the FXTs discovered from Chandra , XMM –Newton, and Swift -X-ray Telescope.