X-ray polarization from accretion disk winds

TL;DR

This paper explores how scattering in accretion disk winds can explain the high X-ray polarization observed in black hole and neutron star systems, challenging conventional models.

Contribution

It proposes that accretion disk winds are a significant source of observed X-ray polarization, providing a new interpretation of recent polarimetric data.

Findings

Wind scattering can reproduce observed polarization levels.

Accretion disk winds may account for polarization in X-ray binaries and AGN.

Challenges conventional accretion geometry models.

Abstract

X-ray polarimetry is a fine tool to probe the accretion geometry and physical processes operating in the proximity of compact objects, black holes and neutron stars. Recent discoveries made by the Imaging X-ray Polarimetry Explorer put our understanding of the accretion picture in question. The observed high levels of X-ray polarization in X-ray binaries and active galactic nuclei are challenging to achieve within the conventional scenarios. In this work we investigate a possibility that a fraction (or even all) of the observed polarized signal arises from scattering in the equatorial accretion disk winds, the slow and extended outflows, which are often detected in these systems via spectroscopic means. We find that the wind scattering can reproduce the levels of polarization observed in these sources.