ipole - semianalytic scheme for relativistic polarized radiative transport

TL;DR

ipole is a new, efficient, and stable public code for covariant polarized radiative transfer, extending previous unpolarized schemes to include polarization effects with analytic solutions for high optical depths.

Contribution

The paper introduces ipole, a novel polarized radiative transfer code that extends covariant schemes with analytic solutions, improving stability and efficiency for relativistic astrophysical modeling.

Findings

Code matches analytic flat space results.

Converges with Dexter's grtrans code on complex models.

Stable and efficient even with high optical and Faraday depths.

Abstract

We describe ${\tt ipole}$, a new public ray-tracing code for covariant, polarized radiative transport. The code extends the ${\tt ibothros}$ scheme for covariant, unpolarized transport using two representations of the polarized radiation field: in the coordinate frame, it parallel transports the coherency tensor; in the frame of the plasma it evolves the Stokes parameters under emission, absorption, and Faraday conversion. The transport step is implemented to be as spacetime- and coordinate- independent as possible. The emission, absorption, and Faraday conversion step is implemented using an analytic solution to the polarized transport equation with constant coefficients. As a result, ${\tt ipole}$ is stable, efficient, and produces a physically reasonable solution even for a step with high optical depth and Faraday depth. We show that the code matches analytic results in flat space, and that it produces results that converge to those produced by Dexter's ${\tt grtrans}$ polarized transport code on a complicated model problem. We expect ${\tt ipole}$ will mainly find applications in modeling Event Horizon Telescope sources, but it may also be useful in other relativistic transport problems such as modeling for the IXPE mission.