Polarization Patterns of the Hotspots Plunging into a Kerr Black Hole

TL;DR

This paper investigates the polarization patterns of hotspots plunging into a Kerr black hole, focusing on the innermost regions and developing models to analyze polarized images and Stokes parameters.

Contribution

It introduces an approximate gravitational lensing function and a simplified synchrotron emission model to study polarization features of non-circular orbits near a Kerr black hole.

Findings

Polarization patterns vary significantly for plunging geodesics.

The model reveals distinctive polarization signatures within the ISCO region.

Polarized images of the plunging region provide insights into black hole accretion dynamics.

Abstract

The multi-wavelength polarized light signals from supermassive black holes have sparked many studies on polarized images of accretion disks and hotspots. However, the polarization patterns within the innermost stable circular orbit (ISCO) region remain to be explored. In this study, we focus on two specific types of orbits, namely the plunging geodesics inward from the ISCO and homoclinic geodesics, to uncover the polarization features associated with non-circular motion in a Kerr spacetime. For an on-axis observer, we specifically develop an approximate function to describe gravitational lensing along the azimuthal direction and establish a simplified synchrotron emission model. Based on these, we analyze the time-integrated polarized images of hotspots and their Stokes parameters. Moreover, we explore the polarized image of the plunging region within a thin accretion disk.