A Time-Dependent Spectral Analysis of $\gamma$ Cassiopeiae

TL;DR

This study analyzes the X-ray emission of $ ext{γ}$ Cassiopeiae, revealing dual variability signals and supporting a white dwarf accretion model with a secondary shock, based on spectral and temporal data from XMM and NuSTAR.

Contribution

It provides new insights into the spectral and temporal features of $ ext{γ}$ Cassiopeiae's X-ray emission, supporting the white dwarf accretion hypothesis with detailed modeling and analysis of simultaneous observations.

Findings

Identification of two distinct variability signals in X-ray data.

Consistent white dwarf properties with optical studies.

Evidence for a secondary shock between disks.

Abstract

We investigated the temporal and spectral features of $\gamma$ Cassiopeiae's X-ray emission within the context of the white dwarf accretion hypothesis. We find that the variabilities present in the X-ray data show two different signals, one primarily due to absorption and the other due to flickering like in non-magnetic cataclysmic variables. We then use this two-component insight to investigate previously un-reported simultaneous XMM and NuSTAR data. The model fitting results find white dwarf properties consistent with optical studies alongside a significant secondary, thermal source. We propose a secondary shock between the Be decretion disk and white dwarf accretion disk as the source. Finally, we analyzed a unique, low-count rate event of the XMM light curve as potential evidence for the white dwarf encountering Be decretion disk structures.