X-ray Super-Flares From Pre-Main Sequence Stars: Flare Modeling

TL;DR

This study models 55 powerful X-ray super-flares from pre-main sequence stars, revealing their properties, correlations with stellar mass, and similarities to solar flares, advancing understanding of stellar magnetic activity.

Contribution

It provides a detailed plasma evolution analysis of a large uniform sample of PMS super-flares, comparing them with other stellar and solar flares, and uncovers new correlations related to stellar mass and magnetic structures.

Findings

PMS super-flares are independent of protoplanetary disks.

Most resemble solar long duration events with CMEs.

Stronger correlations of emission measure and temperature with stellar mass.

Abstract

Getman et al. (2021) reports the discovery, energetics, frequencies, and effects on environs of $>1000$ X-ray super-flares with X-ray energies $E_X \sim 10^{34}-10^{38}$~erg from pre-main sequence (PMS) stars identified in the $Chandra$ MYStIX and SFiNCs surveys. Here we perform detailed plasma evolution modeling of $55$ bright MYStIX/SFiNCs super-flares from these events. They constitute a large sample of the most powerful stellar flares analyzed in a uniform fashion. They are compared with published X-ray super-flares from young stars in the Orion Nebula Cluster, older active stars, and the Sun. Several results emerge. First, the properties of PMS X-ray super-flares are independent of the presence or absence of protoplanetary disks inferred from infrared photometry, supporting the solar-type model of PMS flaring magnetic loops with both footpoints anchored in the stellar surface. Second, most PMS super-flares resemble solar long duration events (LDEs) that are associated with coronal mass ejections. Slow rise PMS super-flares are an interesting exception. Third, strong correlations of super-flare peak emission measure and plasma temperature with the stellar mass are similar to established correlations for the PMS X-ray emission composed of numerous smaller flares. Fourth, a new correlation of loop geometry is linked to stellar mass; more massive stars appear to have thicker flaring loops. Finally, the slope of a long-standing relationship between the X-ray luminosity and magnetic flux of various solar-stellar magnetic elements appears steeper in PMS super-flares than for solar events.