The X-ray emission from Z CMa during an FUor-like outburst and the detection of its X-ray jet

TL;DR

This study observes the FUor object Z CMa during outburst and quiescence, revealing that its X-ray emission is likely from the secondary star's corona and detecting its X-ray jet for the first time.

Contribution

First X-ray detection of Z CMa's jet and analysis of its emission source during an FUor outburst, clarifying the origin of X-ray emission in this system.

Findings

X-ray emission is likely from the secondary star's corona.

Detection of the X-ray jet driven by the secondary star.

X-ray properties remain consistent during outburst and quiescence.

Abstract

Accretion shocks have been recognized as important X-ray emission mechanism for pre-main sequence stars. Yet the X-ray properties of FUor outbursts, events that are caused by violent accretion, have been given little attention. We have observed the FUor object Z CMa during optical outburst and quiescence with Chandra. No significant changes in X-ray brightness and spectral shape are found, suggesting that the X-ray emission is of coronal nature. Due to the binary nature of Z CMa the origin of the X-ray source is ambiguous. However, the moderate hydrogen column density derived from our data makes it unlikely that the embedded primary star is the X-ray source. The secondary star, which is the FUor object, is thus responsible for both the X-ray emission and the presently ongoing accretion outburst, which seem however to be unrelated phenomena. The secondary is also known to drive a large outflow and jet, that we detect here for the first time in X-rays. The distance of the X-ray emitting outflow source to the central star is higher than in jets of low-mass stars.