Characterising 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 ($\sim$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 revolutionising 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 $E_{\mathrm{K},\mathrm{iso}}\sim 10^{51}$ erg, with a half opening angle ${\theta }_c$ $\approx$15${}^{\circ }$, viewed at an angle of ${\theta }_{\mathrm{obs}}$~$\approx$9${}^{\circ }$. We also evaluate EP241107a in the landscape of both EP-discovered FXTs as well as the FXTs discovered from Chandra, XMM-Newton, and Swift-XRT.

13 pages, 9 figures, 2 tables. Submitted to MNRAS

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