X-ray polarization from accretion disk winds

¹ Department of Physics and Astronomy, FI-20014 University of Turku, Finland
² Nordita, Stockholm University and KTH Royal Institute of Technology, Hannes Alfvéns väg 12, SE-10691 Stockholm, Sweden

^⋆ Corresponding author; anaghapradeep.a.nitindala@utu.fi

Received: 27 November 2024
Accepted: 16 January 2025

Abstract

X-ray polarimetry is a fine tool for probing the accretion geometry and physical processes operating in the proximity of compact objects, such as black holes and neutron stars. Recent discoveries made by the Imaging X-ray Polarimetry Explorer question our understanding of the accretion picture. The observed high levels of X-ray polarization in X-ray binaries and active galactic nuclei are challenging to achieve within the conventional scenarios. We investigate the 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 wind scattering can reproduce the levels of polarization that are observed in these sources.