Efficiency of Thin Magnetically-Arrested Disks Around Black Holes

Mark J. Avara; Jonathan C. McKinney; Chris S. Reynolds

doi:10.1093/mnras/stw1643

paper

Efficiency of Thin Magnetically-Arrested Disks Around Black Holes

arXiv:1508.05323 · doi:10.1093/mnras/stw1643

Abstract

The radiative and jet efficiencies of thin magnetized accretion disks around black holes (BHs) are affected by BH spin and the presence of a magnetic field that, when strong, could lead to large deviations from Novikov-Thorne (NT) thin disk theory. To seek the maximum deviations, we perform general relativistic magnetohydrodynamic (GRMHD) simulations of radiatively efficient thin (half-height $H$ to radius $R$ of $H / R \approx 0.10$ ) disks around moderately rotating BHs with $a / M = 0.5$ . First, our simulations, each evolved for more than $70, 000 r_{g} / c$ (gravitational radius $r_{g}$ and speed of light $c$ ), show that large-scale magnetic field readily accretes inward even through our thin disk and builds-up to the magnetically-arrested disk (MAD) state. Second, our simulations of thin MADs show the disk achieves a radiative efficiency of $η_{r} \approx 15%$ (after estimating photon capture), which is about twice the NT value of $η_{r} \sim 8%$ for $a / M = 0.5$ and gives the same luminosity as a NT disk with $a / M \approx 0.9$ . Compared to prior simulations with $≲ 10%$ deviations, our result of an $\approx 80%$ deviation sets a new benchmark. Building on prior work, we are now able to complete an important scaling law which suggest that observed jet quenching in the high-soft state in BH X-ray binaries is consistent with an ever-present MAD state with a weak yet sustained jet.

11 pages, 10 figures, submitted to MNRAS. Movies: https://www.youtube.com/playlist?list=PLqw2cJh32qeH1uJf-O04fbMeq0aheQ8I9

Efficiency of Thin Magnetically-Arrested Disks Around Black Holes

Abstract

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