X-Ray Superflares from Pre-main-sequence Stars: Flare Modeling

Getman et al. report the discovery, energetics, frequencies, and effects on environs of >1000 X-ray superflares with X-ray energies E X ∼ 1034-1038 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 superflares 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 superflares from young stars in the Orion Nebula Cluster, older active stars, and the Sun. Several results emerge. First, the properties of PMS X-ray superflares 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 superflares resemble solar long-duration events that are associated with coronal mass ejections. Slow-rise PMS superflares are an interesting exception. Third, strong correlations of superflare 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 superflares than for solar events.