Chandra HETG X-ray Spectra and Variability of $\pi$ Aqr, a $\gamma$ Cas-type Be star

TL;DR

This study presents high-resolution X-ray spectra and variability analysis of the gamma Cas-type star pi Aqr, suggesting accretion onto a magnetic white dwarf as the source of its hot thermal plasma emission.

Contribution

First detailed high-resolution X-ray spectral and variability analysis of pi Aqr, indicating accretion onto a magnetic white dwarf in an intermediate polar system.

Findings

Detection of emission lines of H-like ions of Mg, Si, S, and Fe.

Observation of significant X-ray flux fluctuations with a ~3400 s period.

Spectrum showed a strong, hard continuum with absence of He-like ions.

Abstract

High-resolution X-ray spectra of $\pi\,$Aqr, a $\gamma\,$Cas-type star, obtained with the Chandra/HETG grating spectrometer, revealed emission lines of H-like ions of Mg, Si, S, and Fe, a strong, hard continuum, and a lack of He-like ions, indicating the presence of very hot thermal plasma. The X-ray light curve showed significant fluctuations, with coherent variability at period of about 3400 seconds in one observation. The hardness ratio was relatively constant except for one observation in which the spectrum was much harder and more absorbed. We interpret the X-ray emission as arising from accretion onto the secondary, which is likely a magnetic white dwarf, an intermediate polar system.