Formation of Magnetically Truncated Accretion Disks in 3D Radiation-Transport Two-Temperature GRMHD Simulations

Abstract

Multi-wavelength observations suggest that the accretion disk in the hard and intermediate states of X-ray binaries (XRBs) and active galactic nuclei (AGN) transitions from a cold, thin disk at large distances into a hot, thick flow close to the black hole. However, the formation, structure and dynamics of such truncated disks are poorly constrained due to the complexity of the thermodynamic, magnetic, and radiative processes involved. We present the first radiation-transport two-temperature general relativistic magnetohydrodynamic (GRMHD) simulations of truncated disks radiating at ∼ 35% of the Eddington luminosity with and without large-scale poloidal magnetic flux. We demonstrate that when a geometrically-thin accretion disk is threaded by largescale net poloidal magnetic flux, it self-consistently transitions at small radii into a two-phase medium of cold gas clumps floating through a hot, magnetically dominated corona. This transition occurs at a well-defined truncation radius determined by the distance out to which the disk is saturated with magnetic flux. The average ion and electron temperatures in the semi-opaque corona reach, respectively, T i 10 10 K and T e 5 × 10 8 K. The system produces radiation, powerful collimated jets and broader winds at the total energy efficiency exceeding 90%, the highest ever energy extraction efficiency from a spinning black hole by a radiatively efficient flow in a GRMHD simulation. This is consistent with jetted ejections observed during XRB outbursts. The two-phase medium can naturally lead to broadened iron line emission observed in the hard state.

Nonthermal emission from the plunging region: a model for the high-energy tail of black hole X-ray binary soft states

“…The equilibrium electron temperature 𝜃 𝑒 decreases from 0.14 (8.9 × 10 8 K) at the ISCO to 0.03 (1.9 × 10 8 ) K at the event horizon (Figure 3). These temperatures are roughly consistent with the inner disk temperatures in two-temperature GRMHD simulations (Liska et al 2022). The temperature decreases towards the event horizon because of the increase in 𝛾 2 , decreasing the power law's overall normalization and shifting the temperature lower because of the continuity requirement (Equation 16).…”

“…For simplicity, in our model, the ion temperature and thus the ratio 𝐻/𝑅 was discontinuous at the ISCO. This discontinuity is not present in full 3D GRMHD simulations; instead, a transition region forms between a thin disk and the hot flow (Hogg & Reynolds 2018;Liska et al 2022). Such a transition region would likely result in a less distinct bump from the thermal electrons in the plunging region.…”

“…Such increased temperature and thus increased ion pressure support will puff up the plunging region beyond a thin disk. The formation of a thick inner disk and a thin outer disk was recently simulated for the first time (Liska et al 2022). For those model parameters, the thin outer disk with 𝐻/𝑟 ∼ 10 −2 expanded to 𝐻/𝑟 ∼ 0.3 within the ISCO.…”

The Long-stable Hard State of XTE J1752-223 and the Disk Truncation Dilemma

“…x log , which is frozen to 0, giving an ionization of 1, or neutral. This includes the density parameter, n e , which is based on our ignorance regarding the radial density profile, since it is generally a highly model-dependent estimate, using both analytical and numerical approaches (Svensson & Zdziarski 1994;Liska et al 2022). The only freely varying parameter of xillverDCp is its normalization, N xil .…”

The Super-Massive Black Hole close environment in Active Galactic Nuclei

“…This hot flow may be formed in different ways, e.g., from disc evaporation [20] or Magneto-Hydro-Dynamic (hereafter MHD) accretionejection processes (e.g. [21,22]). But up to now, none of these models make a complete consensus and none of them is able to explain all the different high-energy properties of compact objects.…”