High Resolution X-ray Spectroscopy of the Nova-Like Cataclysmic Variable BZ Cam using Chandra HETG: Diagnosis of the ADAF-like (Advective) Hot Flow

TL;DR

This study uses Chandra HETG X-ray spectroscopy to analyze BZ Cam, revealing plasma conditions and supporting the presence of an ADAF-like hot accretion flow in this nova-like cataclysmic variable.

Contribution

It provides detailed ionization diagnostics and plasma modeling that confirm the ADAF-like hot flow in BZ Cam, a novel insight into its accretion physics.

Findings

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

Plasma densities of a few 10^{12-14} cm^{-3} and temperatures of 3-6 million K.

Evidence of nonequilibrium ionization conditions and an additional warm absorber.

Abstract

Nova-likes such as BZ Cam are high state Cataclysmic Variables showing hard X-ray emission that can be characterized with advective hot flows in the inner accretion disk. We explore Chandra High Energy Transmission Grating (HETG) observations of BZ~Cam for detailed line diagnosis and ionization conditions in the X-ray regime. We mostly find H- and He-like emission lines of Mg, Si, S, and Fe. All He-like line components of forbidden, intercombination and resonance lines are present. The R ratios of selected lines indicate plasma densities of a few $\times$10$^{12-14}$ cm$^{-3}$ and G ratios reveal temperatures (3-6)$\times$ 10$^6$ K where the Fe lines yield (1-3)$\times$ 10$^7$ K. The H to He line ratios and the R and G ratios show that the plasma is in a nonequilibrium ionization condition, which is consistent with our previous X-ray results and the accretion flow in the X-ray region being an ADAF-like (advective) hot flow. Simultaneous fits of the HEG and MEG spectra or the broadband joint spectra of ROSAT, Chandra zero order and NuSTAR yield temperatures 3.4-6.3 keV using a VNEI model of plasma emission (in XSPEC) or Bremsstrahlung emission. An additional power law is detected above 98\% Confidence Level in the broadband analysis. The orbital variations and the broadband spectra show dipping/veiling of the X-rays and an additional warm absorber model with an ionization parameter log($\xi$) = 2.7 is required at the 3$\sigma$ level, along with the VNEI model where the HEG and MEG simultaneous fits yield the log($\xi$) = 3.6 .