Promise and pitfalls of plasma emission as an exo-space-weather tool

RESUMO

Significant observational effort has been spent on identifying stellar analogues to solar type II and III bursts, which are plasma emission that is produced when coronal mass ejections and fast electron beams, respectively, propagate through the corona and wind. The sensitivity of these bursts to ambient plasma and their association with energetic transient particle flux makes them powerful diagnostics of exo-solar space weather. However, analyses of stellar bursts often rely on the assumption that the coronae of the stars that produce them are similar to the solar corona or that the instability requirements are the same as for the Sun. By extension, the assumption is that the forms of stellar bursts are very similar to that of solar bursts. I introduce a simple framework and the python package, swabs, to predict the shapes of stellar type II and III bursts to understand how they may deviate from the shapes of solar bursts. I present the burst expectations in the range of 10--170 MHz for two well-studied active stars: the M dwarf AD Leonis, and the G dwarf EK Draconis. The results for these stars suggest that the coronae of active stars may lead to bursts that have substantially (1) delayed arrival times to the observing band, (2) shallower drift rates, and (3) longer durations than solar bursts. The hot and fast winds may also inhibit the development of type~II and III bursts, regardless of the Alfvén speed. Non-isothermal winds reduce this inhibition, but may increase the delays and durations of the bursts. This work demonstrates that stellar bursts may deviate radically from their solar analogues. These deviations need to be considered in how we conduct searches for stellar bursts and how we evaluate the coronal conditions that cause the burst structures.