Efficiency of Super-Eddington Magnetically-Arrested Accretion

Jonathan C. McKinney; Lixin Dai; Mark Avara

doi:10.1093/mnrasl/slv115

paper

Efficiency of Super-Eddington Magnetically-Arrested Accretion

arXiv:1508.02433 · doi:10.1093/mnrasl/slv115

Abstract

The radiative efficiency of super-Eddington accreting black holes (BHs) is explored for magnetically-arrested disks (MADs), where magnetic flux builds-up to saturation near the BH. Our three-dimensional general relativistic radiation magnetohydrodynamic (GRRMHD) simulation of a spinning BH (spin $a / M = 0.8$ ) accreting at $\sim 50$ times Eddington shows a total efficiency $\sim 50%$ when time-averaged and total efficiency $≳ 100%$ in moments. Magnetic compression by the magnetic flux near the rotating BH leads to a thin disk, whose radiation escapes via advection by a magnetized wind and via transport through a low-density channel created by a Blandford-Znajek (BZ) jet. The BZ efficiency is sub-optimal due to inertial loading of field lines by optically thick radiation, leading to BZ efficiency $\sim 40%$ on the horizon and BZ efficiency $\sim 5%$ by $r \sim 400 r_{g}$ (gravitational radii) via absorption by the wind. Importantly, radiation escapes at $r \sim 400 r_{g}$ with efficiency $η \approx 15%$ (luminosity $L \sim 50 L_{Edd}$ ), similar to $η \approx 12%$ for a Novikov-Thorne thin disk and beyond $η ≲ 1%$ seen in prior GRRMHD simulations or slim disk theory. Our simulations show how BH spin, magnetic field, and jet mass-loading affect the radiative and jet efficiencies of super-Eddington accretion.

5 pages, 4 figures, MNRAS letters, in press, Movies: http://www.youtube.com/playlist?list=PLwa71jI0sY_AD9e8-7DXmJm4AHWFdARtT

Efficiency of Super-Eddington Magnetically-Arrested Accretion

Abstract

References in corpus (4)

Cited by in corpus (67)