Turbulence Heating and Nonthermal Radiation From MRI-induced Accretion onto Low-Luminosity Black Holes E.Liang, G.Hilburn, S.M.Liu, H. Li, C. Gammie, M. Boettcher Presentation at the 2007 APS/DPP Meeting in Orlando Work partially supported by NSF, NASA, LANL

(from S. Liu et al ) High-energy emission of black hole SgrA* examplifies low-luminosity accretion which requires energization above the level predicted by conventional thermal SSC model

weakly magnetized initial torus MRI-induced accretion flow with saturated MHD turbulence compressional heating of ions coulomb heating of electrons by virial ions thermal cyclotron emission at low energy SSC + EC emission at high energy turbulence energization of nonthermal electrons and ions synchrotron emission by nonthermal electrons pion decay emission of Nonthermal ions SSC+EC of nonthermal electrons thermal disk paradigm new approach

B2B2 density 256x256 t=2002 MRI-induced flow from global GRMHD simulations

256x256512x512 B 2 t=914 Extend turbulence spectrum by increasing resolution

256x x512 density t=914

Based on current parallelism, it is difficult to make long GRMHD runs using much larger than 1000x1000 grid. This still leaves each MHD zone > 10 6 Debye length. How can we tackle the subgrid microphysics? Impractical to simulate dissipation with explicit PIC code with zones ≤ Debye length. ( >10 12 zones in 2D). Two approaches: 1.Extrapolate turbulence spectrum to subgrid scales as power law and solve Fokker-Planck equation for wave-particle interaction 2. Use implicit PIC code with large zones (>> Debye length) and large time steps. We will employ both methods and compare their results

Once the electron spectrum for each zone is obtained, we can couple it to our 2D Monte Carlo (MC) photon transport code via implicit schemes. This part of computation is easily parallelized since MC photon time steps >> electron evolution time and MC is fully parallel by itself.

MC photon transport

Sample output of MC-FP code with wave spectrum ~   k -5/3 electron spectraphoton spectra (from Boettcher and Liang 2002)

Polar grid of General Relativistic MHD simulation output is mapped onto the cylindrical grid of Monte Carlo photon transport B2B2 density

Hard tail would require nonthermal acceleration of electrons/ions by MHD turbulence above thermal heating synchrotron peak bremsstrahlung peak Sample spectrum from 2D MC code with GRMHD results as input (at high density so that bremsstrahlung dominates over Compton and without turbulence heating)

PIC simulation of turbulence cascade converts EM energy into particle energy and formation of power-law in both e+e- and e-ion plasmas. sample input: magnetosonic waves with =1024c/  pe and  B 2 /4  c 2 = 100

Development of current instability is key to the cascade of EM turbulence to smaller and smaller scales

Summary 1.Many BH exhibit nonthermal hard spectra that strongly suggest nonthermal energization of electrons/ions by EM turbulence. 2.We propose to study such energization using turbulence self-generated in MRI - induced accretion flows. 3.We will use both FP and implicit PIC codes to study dissipation of EM turbulence at the sub-grid scale. 4.We propose to couple the resultant electron spectra to MC photon transport.