The effect of two-temperature post-shock accretion flow on the linear polarization pulse in magnetic cataclysmic variables

TL;DR

This study compares the polarized radiation from one- and two-temperature models of post-shock accretion flows in magnetic cataclysmic variables, highlighting the importance of two-temperature modeling for accurate polarization predictions.

Contribution

It introduces a detailed analysis of how two-temperature hydrodynamics affects polarization signals in mCVs, emphasizing the need for two-temperature models in polarization studies.

Findings

Two-temperature flows can produce different polarization pulse patterns than one-temperature flows.

Modeling two-temperature flows is crucial for accurate polarization predictions in ultraviolet observations.

Circular polarization predictions are similar between models, but linear polarization pulses differ significantly.

Abstract

The temperatures of electrons and ions in the post-shock accretion region of a magnetic cataclysmic variable (mCV) will be equal at sufficiently high mass flow rates or for sufficiently weak magnetic fields. At lower mass flow rates or in stronger magnetic fields, efficient cyclotron cooling will cool the electrons faster than the electrons can cool the ions and a two-temperature flow will result. Here we investigate the differences in polarized radiation expected from mCV post-shock accretion columns modeled with one- and two-temperature hydrodynamics. In an mCV model with one accretion region, a magnetic field >~30 MG and a specific mass flow rate of ~0.5 g/cm/cm/s, along with a relatively generic geometric orientation of the system, we find that in the ultraviolet either a single linear polarization pulse per binary orbit or two pulses per binary orbit can be expected, depending on the accretion column hydrodynamic structure (one- or two-temperature) modeled. Under conditions where the physical flow is two-temperature, one pulse per orbit is predicted from a single accretion region where a one-temperature model predicts two pulses. The intensity light curves show similar pulse behavior but there is very little difference between the circular polarization predictions of one- and two-temperature models. Such discrepancies indicate that it is important to model some aspect of two-temperature flow in indirect imaging procedures, like Stokes imaging, especially at the edges of extended accretion regions, were the specific mass flow is low, and especially for ultraviolet data.