On the source of the Fe K-alpha emission in T Tauri Stars. Radiation induced by relativistic electrons during flares. An application to RY Tau

TL;DR

This study investigates the origin of Fe K-alpha emission in T Tauri Stars, proposing that relativistic electrons during flares produce this emission, supported by Monte Carlo simulations matching observations of RY Tau.

Contribution

The paper introduces a novel simulation approach to model electron-induced Fe K-alpha emission in T Tauri Stars, linking magnetic reconnection flares to observed X-ray features.

Findings

Relativistic electron beams can produce Fe K-alpha emission consistent with observations.

Simulations show a hot spot with strong Fe K-alpha emission at impact points.

The observed Fe K-alpha in RY Tau can be explained by electron beams from magnetic reconnection.

Abstract

T Tauri Stars (TTSs) are magnetically active stars that accrete matter from the inner border of the surrounding accretion disc; plasma gets trapped into the large scale magnetic structures and falls onto the star, heating the surface through the so-called accretion shocks. The X-ray spectra of the TTSs show prominent Fe II Kalpha fluorescence emission at 6.4keV that cannot be explained in a pure accretion scenario. Neither, it can be produced by the hot coronal plasma. TTSs display all signs of magnetic activity and magnetic reconnection events are expected to occur frequently. In these events, electrons may get accelerated to relativistic speeds and their interaction with the environmental matter may result in Fe Kalpha emission. It is the aim of this work to evaluate the expected Fe Kalpha emission in the context of the TTS research and compare it with the actual Fe Kalpha measurements obtained during the flare detected while monitoring RY Tau with the XMM-Newton satellite. The propagation of high-energy electrons in dense gas generates a cascade of secondary particles that results in an electron shower of random nature whose evolution and radiative throughput is simulated in this work using the Monte Carlo code PENELOPE. A set of conditions representing the environment of the TTSs where these showers may impinge has been taken into account to generate a grid of models that can aid to the interpretation of the data. The simulations show that the electron beams produce a hot spot at the point of impact; strong Fe Kalpha emission and X-ray continuum radiation are produced by the spot. This emission is compatible with RY Tau observations. The Fe Kalpha emission observed in TTSs could be produced by beams of relativistic electrons accelerated in magnetic reconnection events during flares.