The role of complex ionized absorber in the soft X-ray spectra of Intermediate Polars

TL;DR

This study introduces a new ionized absorber model to interpret soft X-ray spectra of Intermediate Polars, revealing complex absorption features and challenging previous assumptions about the soft excess component.

Contribution

The paper develops the zxipab model for ionized absorption and applies it to broadband spectra of two IPs, providing insights into the pre-shock region's geometry and ionization processes.

Findings

The model fits many emission lines from medium Z elements.

Fails to fully explain some He-like triplets, indicating photo-ionization.

No strong evidence for a blackbody soft excess in the spectra.

Abstract

In magnetic Cataclysmic Variables (mCVs), X-ray radiation originates from the shock heated multi-temperature plasma in the post-shock region near the white dwarf surface. These X-rays are modified by a complex distribution of absorbers in the pre-shock region. The presence of photo-ionized lines and warm absorber features in the soft X-ray spectra of these mCVs suggests that these absorbers are ionized. We developed the ionized complex absorber model zxipab, which is represented by a power-law distribution of ionized absorbers in the pre-shock flow. Using the ionized absorber model zxipab along with a cooling flow model and a reflection component, we model the broadband Chandra/HETG and NuSTAR spectra of two IPs: NY Lup and V1223 Sgr. We find that this model describes well many of the H and He like emission lines from medium Z elements, which arises from the collisionally excited plasma. However the model fails to account for some of the He like triplets from medium Z elements, which points towards its photo-ionization origin. We do not find a compelling evidence for a blackbody component to model the soft excess seen in the residuals of the Chandra/HETG spectra, which could be due to the uncertainties in estimation of the interstellar absorption of these sources using Chandra/HETG data and/or excess fluxes seen in some photo-ionized emission lines which are not accounted by the cooling flow model. We describe the implications of this model with respect to the geometry of the pre-shock region in these two IPs.