http://arxiv.org/abs/2209.12081
We present two general relativistic radiation magnetohydrodynamics (GRRMHD) simulations of magnetically arrested disks (MADs) around non-spinning ($a_=0$) and spinning ($a_=0.9$) supermassive black holes (BHs). In each simulation, the mass accretion rate is decreased with time such that we sample Eddington-scaled rates over the range $3 \gtrsim \dot{M}/\dot{M}{\rm{Edd}}\gtrsim 0.3$. For the non-spinning BH model, the total and radiative efficiencies increase as the accretion rate decreases, varying over the range $\eta{\rm{tot}}\sim9-16\%$ and $\eta_{\rm{rad}}\sim6-12\%$, respectively. This model shows very little jet activity. In contrast, the spinning BH model has a strong relativistic jet powered by spin energy extracted from the BH. The jet power declines with accretion rate such that $\eta_{\rm{jet}}\sim 18-39\%$ while the total and radiative efficiencies are $\eta_{\rm{tot}}\sim 64-100\%$ and $\eta_{\rm{rad}}\sim 45-79\%$, respectively. We confirm that mildly sub-Eddington disks can extract substantial power from a spinning BH, provided they are in the MAD state. The jet profile out to $100\, GM/c^2$ is roughly parabolic with a power-law index of $k\approx0.43-0.53$ during the sub-Eddington evolution. Both models show significant variability in the outgoing radiation which is likely associated with episodes of magnetic flux eruptions. The $a_=0.9$ model shows semi-regular variations with a period of $\sim2000\, GM/c^3$ over the final $\sim10,000\, GM/c^3$ of the simulation, which suggests that magnetic flux eruptions may be an important source of quasi-periodic variability. For the simulated accretion rates, the $a_=0$ model is spinning up while the $a_=0.9$ model is spinning down. Spinup-spindown equilibrium of the BH will likely be achieved at $0.5 < a_{,{\rm{eq}}} < 0.6$, assuming continuous accretion in the MAD state.
B. Curd and R. Narayan
Tue, 27 Sep 22
15/89
Comments: 23 pages, 18 figures
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