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

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. This is the largest sample of highly energetic 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 super-flares are independent of the presence or absence of protoplanetary disks, 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 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 likely composed of numerous smaller flares. Fourth, a new correlation of loop geometry is linked to stellar mass; more massive stars 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.