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Register a new userTwo-Temperature GRRMHD Simulations of M87
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We present axisymmetric two-temperature general relativistic radiation magnetohydrodynamic (GRRMHD) simulations of the inner region of the accretion flow onto the supermassive black hole M87. We address uncertainties from previous modeling efforts through inclusion of models for (1) self-consistent dissipative and Coulomb electron heating (2) radiation transport (3) frequency-dependent synchrotron emission, self-absorption, and Compton scattering. We adopt a distance $D=16.7$ Mpc, an observer angle $theta = 20^{circ}$, and consider black hole masses $M/M_{odot} = (3.3times10^{9}, 6.2times10^{9})$ and spins $a_{star} = (0.5, 0.9375)$ in a four-simulation suite. For each $(M, a_{star})$, we identify the accretion rate that recovers the 230 GHz flux from VLBI measurements. We report on disk thermodynamics at these accretion rates ($dot{M}/dot{M}_{mathrm{Edd}} sim 10^{-5}$). The disk remains geometrically thick; cooling does not lead to a thin disk component. While electron heating is dominated by Coulomb rather than dissipation for $r gtrsim 10 GM/c^2$, the accretion disk remains two-temperature. Radiative cooling of electrons is not negligible, especially for $r lesssim 10 GM/c^2$. The Compton $y$ parameter is of order unity. We then compare derived and observed or inferred spectra, mm images, and jet powers. Simulations with $M/M_{odot} = 3.3times10^{9}$ are in conflict with observations. These simulations produce mm images that are too small, while the low-spin simulation also overproduces X-rays. For $M/M_{odot} = 6.2times10^{9}$, both simulations agree with constraints on radio/IR/X-ray fluxes and mm image sizes. Simulation jet power is a factor $10^2-10^3$ below inferred values, a possible consequence of the modest net magnetic flux in our models.
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We present axisymmetric numerical simulations of radiatively inefficient accretion flows onto black holes combining general relativity, magnetohydrodynamics, self-consistent electron thermodynamics, and frequency-dependent radiation transport. We investigate a range of accretion rates up to $10^{-5} dot{M}_{mathrm{Edd}}$ onto a $10^8 M_{odot}$ black hole with spin $a_{star} = 0.5$. We report on averaged flow thermodynamics as a function of accretion rate. We present the spectra of outgoing radiation and find that it varies strongly with accretion rate, from synchrotron-dominated in the radio at low $dot{M}$ to inverse Compton-dominated at our highest $dot{M}$. In contrast to canonical analytic models, we find that by $dot{M} approx 10^{-5} dot{M}_{mathrm{Edd}}$, the flow approaches $sim 1%$ radiative efficiency, with much of the radiation due to inverse Compton scattering off Coulomb-heated electrons far from the black hole. These results have broad implications for modeling of accreting black holes across a large fraction of the accretion rates realized in observed systems.
We report results from general relativistic radiation MHD (GRRMHD) simulations of a super-Eddington black hole (BH) accretion disk formed as a result of a tidal disruption event (TDE). We consider the fiducial case of a solar mass star on a mildly penetrating orbit disrupted by a supermassive BH of mass $10^6 , M_odot$, and consider the epoch of peak fall back rate. We post-process the simulation data to compute viewing angle dependent spectra. We perform a parameter study of the dynamics of the accretion disk as a function of BH spin and magnetic flux, and compute model spectra as a function of the viewing angle of the observer. We also consider detection limits based on the model spectra. We find that an accretion disk with a relatively weak magnetic field around the BH (so-called SANE regime of accretion) does not launch a relativistic jet, whether or not the BH is rotating. Such models reasonably reproduce several observational properties of non-jetted TDEs. The same is also true for a non-rotating BH with a strong magnetic field (MAD regime). One of our simulations has a rapidly rotating BH (spin parameter 0.9) as well as a MAD accretion disk. This model launches a powerful relativistic jet, which is powered by the BH spin energy. It reproduces the high energy emission and jet structure of the jetted TDE Swift J1644+57 surprisingly well. Jetted TDEs may thus correspond to the subset of TDE systems that have both a rapidly spinning BH and MAD accretion.
We use the public code ebhlight to carry out 3D radiative general relativistic magnetohydrodynamics (GRMHD) simulations of accretion onto the supermassive black hole in M87. The simulations self-consistently evolve a frequency-dependent Monte Carlo description of the radiation field produced by the accretion flow. We explore two limits of accumulated magnetic flux at the black hole (SANE and MAD), each coupled to several sub-grid prescriptions for electron heating that are motivated by models of turbulence and magnetic reconnection. We present convergence studies for the radiation field and study its properties. We find that the near-horizon photon energy density is an order of magnitude higher than is predicted by simple isotropic estimates from the observed luminosity. The radially dependent photon momentum distribution is anisotropic and can be modeled by a set of point-sources near the equatorial plane. We draw properties of the radiation and magnetic field from the simulation and feed them into an analytic model of gap acceleration to estimate the very high energy (VHE) gamma-ray luminosity from the magnetized jet funnel, assuming that a gap is able to form. We find luminosities of $rm sim 10^{41} , erg , s^{-1}$ for MAD models and $rm sim 2times 10^{40} , erg , s^{-1}$ for SANE models, which are comparable to measurements of M87s VHE flares. The time-dependence seen in our calculations is insufficient to explain the flaring behavior. Our results provide a step towards bridging theoretical models of near-horizon properties seen in black hole images with the VHE activity of M87.
We present the results of two-temperature magnetohydrodynamic simulations of the propagation of sub-relativistic jets of active galactic nuclei. The dependence of the electron and ion temperature distributions on the fraction of electron heating fe at the shock front is studied for fe=0, 0.05, and 0.2. Numerical results indicate that in sub-relativistic, rarefied jets, the jet plasma crossing the terminal shock forms a hot, two-temperature plasma in which the ion temperature is higher than the electron temperature. The two-temperature plasma expands and forms a backflow referred to as a cocoon, in which the ion temperature remains higher than the electron temperature for longer than 100 Myr. Electrons in the cocoon are continuously heated by ions through Coulomb collisions, and the electron temperature thus remains at Te > 10^9 K in the cocoon. X-ray emissions from the cocoon are weak because the electron number density is low. Meanwhile, soft X-rays are emitted from the shocked intracluster medium surrounding the cocoon. Mixing of the jet plasma and the shocked intracluster medium through the Kelvin--Helmholtz instability at the interface enhances X-ray emissions around the contact discontinuity between the cocoon and shocked intracluster medium.
We revisit the XMM-Newton observation of M87 focusing our attention on the temperature structure. We find that spectra for most regions of M87 can be adequately fit by single temperature models. Only in a few regions, which are cospatial with the E and SW radio arms, we find evidence of a second temperature. The cooler component (kT ~ 0.8-1 keV) fills a small volume compared to the hotter component (kT ~ 1.6-2.5 keV), it is confined to the radio arms rather than being associated with the potential well of the central cD and is probably structured in blobs with typical sizes smaller than a few 100 pc. Thermal conduction must be suppressed for the cool blobs to survive in the hotter ambient gas. Since the cool gas is observed only in those regions of M87 where we have evidence of radio halos our results favor models in which magnetic fields play a role in suppressing heat conduction. The entropy of the cool blobs is in general smaller than that of the hot phase gas thus cool blobs cannot originate from adiabatic evolution of hot phase gas entrained by buoyant radio bubbles, as suggested by Churazov et al. (2001). An exploration of alternative origins for the cool gas leads to unsatisfactory results.
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