Radiation RMHD accretion flows around spinning AGNs: a comparative study of MAD and SANE state

TL;DR

This study compares MAD and SANE accretion states around spinning black holes using 2D radiation RMHD simulations, revealing differences in magnetic field strength, luminosity contributions, and oscillation behaviors, with implications for understanding AGN accretion physics.

Contribution

It provides a detailed comparative analysis of MAD and SANE states in radiation RMHD accretion flows, including the conditions for MAD formation and spectral characteristics.

Findings

MAD state occurs at higher initial magnetic fields.

Luminosity dominated by bremsstrahlung due to dense torus.

Similar QPOs observed in both MAD and SANE states.

Abstract

In our study, we examine a 2D radiation, relativistic, magnetohydrodynamics (Rad-RMHD) accretion flows around a spinning supermassive black hole. We begin by setting an initial equilibrium torus around the black hole, with an embedded initial magnetic field inside the torus. The strength of the initial magnetic field is determined by the plasma beta parameter, which is the ratio of the gas pressure to the magnetic pressure. In this paper, we perform a comparative study of the `magnetically arrested disc (MAD)' and `standard and normal evolution (SANE)' states. We observe that MAD state is possible for comparatively high initial magnetic field strength flow. Additionally, we also adopt a self-consistent two-temperature model to evaluate the luminosity and energy spectrum for our model. We observe that the total luminosity is mostly dominated by bremsstrahlung luminosity compared to the synchrotron luminosity due to the presence of highly dense torus. We also identify similar quasi-periodic oscillations (QPOs) for both MAD and SANE states based on power density spectrum analysis. Furthermore, our comparative study of the energy spectrum does not reveal any characteristic differences between MAD and SANE states. Lastly, we note that the MAD state is possible for both prograde and retrograde accretion flow.