Multiwavelength Signatures of Magnetic Activity from Young Stellar Objects in the LkH\alpha101 Cluster

TL;DR

This study investigates the multi-wavelength magnetic activity of young stellar objects in the LkHα101 cluster, revealing nonthermal radio emission, variability patterns, and unique correlations that enhance understanding of stellar magnetic phenomena.

Contribution

It provides the first simultaneous X-ray and multi-frequency radio observations of young stars, uncovering new insights into their emission mechanisms and variability behaviors.

Findings

Radio emission is predominantly nonthermal even in stars with disks.

Significant variability occurs on multiple timescales, affecting radio more than X-ray emissions.

Inverse correlation between radio flux and spectral index suggests particle acceleration processes.

Abstract

[abridged] We describe the results of our multi-wavelength observing campaign on the young stellar objects in the LkH$\alpha$101 cluster. Our simultaneous X-ray and multi-frequency radio observations are unique in providing simultaneous constraints on short-timescale variability at both wavelengths as well as constraints on the thermal or nonthermal nature of radio emission from young stars. Focussing in on radio-emitting objects and the multi-wavelength data obtained for them, we find that multi-frequency radio data indicate nonthermal emission even in objects with infrared evidence for disks. We find radio variability on timescales of decades, days and hours. About half of the objects with X-ray and radio detections were variable at X-ray wavelengths, despite lacking large-scale flares or large variations. Variability appears to be a bigger factor affecting radio emission than X-ray emission. A star with infrared evidence for a disk, [BW88]~3, was observed in the decay phase of a radio flare. In this object and another ([BW88]~1), we find an inverse correlation between radio flux and spectral index which contrasts with behavior seen in the Sun and active stars. We interpret this behavior as the repopulation of the hardest energy electrons due to particle acceleration. A radio and X-ray source lacking an infrared counterpart, [BW88]~1, may be near the substellar limit; its radio properties are similar to other cluster members, but its much higher radio to X-ray luminosity ratio is reminiscent of behavior in nearby very low mass stars/brown dwarfs. We find no correspondence between signatures of particle acceleration and those of plasma heating, both time-averaged and time-variable. The lack of correlated temporal variability in multi-wavelength behavior, the breakdown of multi-wavelength correlations of...