Circular orbits and polarized images of charged particles orbiting Kerr black hole with a weak magnetic field

TL;DR

This paper analyzes the circular orbits of charged particles around Kerr black holes in weak magnetic fields, deriving analytical expressions for stable orbit radii and simulating polarized images to understand polarization effects.

Contribution

It provides an analytical approximation for the innermost stable circular orbit of charged particles and semi-analytical polarized images considering various parameters around Kerr black holes.

Findings

Magnetic field and charge-to-mass ratio significantly affect polarization rotation.

Polarized flux magnitude varies with spin, observational angle, and orbit direction.

Analytical expressions for stable orbit radii are derived for weak magnetic fields.

Abstract

In this work, we study circular motions of charged particles and their polarized images around the Kerr black hole immersed in a weak magnetic field. We pay special attention to the case that both the magnetic field and the charge-to-mass ratio are not big, thus the effective potential along the radial motion reduce to a cubic form approximately so that we can express the radius of the innermost stable circular orbit analytically in terms of the energy and angular momentum of charged particles. Moreover, we computed the polarized synchrotron radiations of these particles and obtained the polarized images semi-analytically for various spins, observational angles and prograde and retrograde orbits. In particular, We find that these parameters have significant impacts on the polarization rotation and the magnitude of the polarization flux.