Investigating the Properties of the Relativistic Jet and Hot Corona in AGN with X-ray Polarimetry

TL;DR

This paper reviews recent discoveries in AGN physics enabled by X-ray polarimetry from IXPE, revealing insights into jet magnetic fields, particle acceleration, and corona geometry in active galactic nuclei.

Contribution

It provides new observational evidence on magnetic field structures and corona shapes in AGN using the novel X-ray polarimetry data from IXPE.

Findings

Jets show evidence of helical magnetic fields.

Blazar polarization supports energy-stratified shock acceleration.

Corona geometry is consistent with a slab-like or wedge shape.

Abstract

X-ray polarimetry has been suggested as a prominent tool for investigating the geometrical and physical properties of the emissions from active galactic nuclei (AGN). The successful launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 9 December 2021 has expanded the previously restricted scope of polarimetry into the X-ray domain, enabling X-ray polarimetric studies of AGN. Over a span of two years, IXPE has observed various AGN populations, including blazars and radio-quiet AGN. In this paper, we summarize the remarkable discoveries achieved thanks to the opening of the new window of X-ray polarimetry of AGN through IXPE observations. We will delve into two primary areas of interest: first, the magnetic field geometry and particle acceleration mechanisms in the jets of radio-loud AGN, such as blazars, where the relativistic acceleration process dominates the spectral energy distribution; and second, the geometry of the hot corona in radio-quiet AGN. Thus far, the IXPE results from blazars favor the energy-stratified shock acceleration model, and they provide evidence of helical magnetic fields inside the jet. Concerning the corona geometry, the IXPE results are consistent with a disk-originated slab-like or wedge-like shape, as could result from Comptonization around the accretion disk.