Transient sources at the highest angular resolution

TL;DR

This paper reviews high-resolution radio observations of transient phenomena in stellar binary systems, including T Tauri stars and X-ray binaries, highlighting how VLBI techniques enhance understanding of their magnetic and jet activities.

Contribution

It presents new VLBI observational results of binary systems at different evolutionary stages, linking radio emission evolution to magnetic field topology and jet characteristics.

Findings

VLBI resolves binary separation in T Tauri system V773 Tau A.

Radio emission evolution informs magnetic field topology.

Comparison of radio jets in X-ray binaries and gamma-ray binaries.

Abstract

By definition transients are sudden events, some, like supernovae, are catastrophic, while others might be due to recurrent phenomena. The aim of studying transients is to reveal the physical conditions causing them, in this sense ideal targets for monitoring are transients in binary systems. In these systems the physical process responsible for the transient depends directly or indirectly on the interaction of the two components of the system. Here I report on transients in stellar binary systems at two extremes of stellar evolution: a T~Tauri system formed by two young low mass stellar objects, and X-ray binary systems formed by a star and a neutron star or a black hole, i.e., end points in the life of massive stars. VLBI observations of the young binary system V773 Tau A resolve the binary separation and can be overlapped with the optical frame. Consecutive VLBI observations showing the evolution of the radio emission with respect to the two stellar objects are an unvaluable tool for a better understanding of the magnetic field topology of T Tauri stars. The characteristics of radio jets in X-ray binaries are summarised and compared with those of the radio emission of the gamma-ray binary LS I +61303. Timing analysis of radio and Fermi-LAT observations provide constraints for theoretical models that can be tested by VLBI observations.