The Effects of Magnetic Field Strength on Properties of Wind Generated from Hot Accretion Flow

TL;DR

This study investigates how magnetic field strength influences wind properties in hot accretion flows around black holes, revealing that wind exists in both weakly and strongly magnetized conditions with varying driving forces.

Contribution

It provides a comparative analysis of wind characteristics in weakly and strongly magnetized accretion flows using MHD simulations, highlighting the different driving mechanisms.

Findings

Wind exists in both weakly and strongly magnetized flows.

Wind power ranges from 10^{-4} to 10^{-3} of mass inflow rate times c squared.

Magnetic field strength slightly increases wind power.

Abstract

Observations indicate that wind can be generated in hot accretion flow. By performing numerical simulations, Yuan et al. studied the detailed properties of wind generated from weakly magnetized accretion flow. However, properties of wind generated from strongly magnetized hot accretion flow have not been studied. In this paper, we study the properties of wind generated from both weakly and strongly magnetized accretion flow. We focus on how the magnetic field strength affects the wind properties. We solve time-steady two-dimensional magnetohydrodynamic (MHD) equations of black hole accretion in the presence of large-scale magnetic field. We assume self-similarity in radial direction. The magnetic field is assumed to be evenly symmetric with the equatorial plane. We find that wind exists in both weakly and strongly magnetized accretion flow. When magnetic field is weak (magnetic pressure is more than 2 orders of magnitude smaller than gas pressure), wind is driven by gas pressure gradient and centrifugal forces. When magnetic field is strong (magnetic pressure is slightly smaller than gas pressure), wind is driven by gas pressure gradient and magnetic pressure gradient forces. The power of wind in strongly magnetized case is just slightly larger than that in weakly magnetized case. The power of wind lies in a range $ P_W \sim 10^{-4}-10^{-3} \dot M_{\rm in} c^2 $, with $ \dot M_{\rm in} $ and $ c $ being mass inflow rate and speed of light, respectively. The possible role of wind in active galactic nuclei feedback is briefly discussed.