A Survey of High Contrast Stellar Flares Observed by Chandra

TL;DR

This survey analyzes high-contrast X-ray stellar flares observed by Chandra, revealing correlations between flare properties, magnetic fields, and the presence of disks in pre-main sequence stars.

Contribution

It extends the study of stellar flares by analyzing a larger sample from the ANCHORS database and correlates flare characteristics with infrared data indicating disks.

Findings

Longest flare loops are associated with stars having disks.

Long flares tend to be more tenuous.

Wide range of loop lengths suggests diverse flare mechanisms.

Abstract

The X-ray light curves of pre-main sequence stars can show variability in the form of flares altering a baseline characteristic activity level; the largest X-ray flares are characterized by a rapid rise to more than 10 times the characteristic count rate, followed by a slower quasi-exponential decay. Analysis of these high-contrast X-ray flares enables the study of the innermost magnetic fields of pre-main sequence stars. We have scanned the ANCHORS database of Chandra observations of star-forming regions to extend the study of flare events on pre-main sequence stars both in sky coverage and in volume. We developed a sample of 30 high-contrast flares out of the 14,000 stars of various ages and masses available in ANCHORS at the start of our study. Applying methods of time-resolved spectral analysis, we obtain the temperatures, confining magnetic field strengths, and loop lengths of these bright, energetic flares. The results of the flare analysis are compared to the 2MASS and Spitzer data available for the stars in our sample. We find that the longest flare loop lengths (of order several stellar radii) are only seen on stars whose IR data indicates the presence of disks. This suggests that the longest flares may stretch all the way to the disk. Such long flares tend to be more tenuous than the other large flares studied. A wide range of loop lengths are observed, indicating that different types of flares may occur on disked young stellar objects.