Polarization Signatures from GRMHD Simulations of Black Hole Accretion

TL;DR

This chapter discusses the potential of X-ray polarimetry combined with GRMHD simulations to improve understanding of black hole accretion disks, jets, and coronae, highlighting current challenges and future prospects.

Contribution

It emphasizes the need for more polarization simulation results and advocates for community efforts to advance X-ray polarimetry studies of accreting compact objects.

Findings

Polarization signatures can reveal disk and jet properties.

Current results are limited; more simulations are needed.

Radio polarimetry has already provided insights into black hole environments.

Abstract

This chapter tells the still-unfolding story of extracting polarization signatures from general relativistic magnetohydrodynamics simulations of accretion disks. In some sense, this effort is premature as there are still very few results of this kind. Much more abundant are phenomenological models. Nevertheless, we feel now is the time to rally the community to this cause. Since the focus of this book is on X-ray polarimetry, we focus exclusively on simulations of accretion onto compact objects. Most of the relevant work so far has been on black hole accretion disks, though neutron stars are also viable targets for X-ray polarimetry. The focus of our chapter is on how X-ray polarimetry coupled with accretion simulations might help us better understand properties of the disks, coronae, and jets that are the dominant components of accreting compact sources. We briefly illustrate the promise of this technique by demonstrating how it has already been used in the case of the Event Horizon Telescope (using radio polarimetry). We also speculate about where this field may be heading in the near future.