Predicting the time variation of radio emission from MHD simulations of a flaring T-Tauri star

TL;DR

This study models the time-dependent radio emission from a flaring T-Tauri star using 3D MHD simulations, predicting multi-frequency intensity and polarization evolution to better understand stellar magnetic activity.

Contribution

First to combine 3D MHD simulations with gyrosynchrotron emission modeling to predict radio spectra and polarization from flaring T-Tauri stars.

Findings

Peak flux occurs around 20-30 GHz and decreases over time.

Radio luminosity matches observed values for T-Tauri stars.

Polarization can reach 10-30% with complex evolving structure.

Abstract

We model the time dependent radio emission from a disk accretion event in a T-Tauri star using 3D, ideal magnetohydrodynamic simulations combined with a gyrosynchrotron emission and radiative transfer model. We predict for the first time, the multi-frequency (1$-$1000 GHz) intensity and circular polarisation from a flaring T-Tauri star. A flux tube, connecting the star with its circumstellar disk, is populated with a distribution of non-thermal electrons which is allowed to decay exponentially after a heating event in the disk and the system is allowed to evolve. The energy distribution of the electrons, as well as the non-thermal power law index and loss rate, are varied to see their effect on the overall flux. Spectra are generated from different lines of sight, giving different views of the flux tube and disk. The peak flux typically occurs around 20$-$30 GHz and the radio luminosity is consistent with that observed from T-Tauri stars. For all simulations, the peak flux is found to decrease and move to lower frequencies with elapsing time. The frequency-dependent circular polarisation can reach 10$-$30$\%$ but has a complex structure which evolves as the flare evolves. Our models show that observations of the evolution of the spectrum and its polarisation can provide important constraints on physical properties of the flaring environment and associated accretion event.