On the comparison of AGN with GRMHD simulations: I. Sgr A*

Abstract

We present models of Galactic Center emission in the vicinity of Sagittarius A* that use parametrizations of the electron temperature or energy density. These models include those inspired by two-temperature general relativistic magnetohydrodynamic (GRMHD) simulations as well as jet-motivated prescriptions generalizing equipartition of particle and magnetic energies. From these models, we calculate spectra and images and classify them according to their distinct observational features. Some models produce morphological and spectral features, e.g., image sizes, the sub-mm bump and low frequency spectral slope compatible with observations. Models with spectra consistent with observations produce the most compact images, with the most prominent, asymmetric photon rings. Limb brightened outflows are also visible in many models. Of all the models we consider, that which represents the current data the best is one in which electrons are relativistically hot when magnetic pressure is larger than the thermal pressure, but cold (i.e., negligibly contributing to the emission) otherwise. This work is part of a series also applying the "observing" simulations methodology to near-horizon regions of supermassive black holes in M87 and 3C 279.

Spectral and imaging properties of Sgr A* from high-resolution 3D GRMHD simulations with radiative cooling

“…We carry out the simulation with one set of R l = 1 and R h = 20, and the resulting spectrum is in good agreement with the observed data (shaded blue line in Figure 10), except for the mismatch of the NIR powerlaw slope: it reproduces the observed NIR emission while keeping the X-ray emission within the observed maximum limit in the quiescent state. This reinforces the point that SEDs calculated from GRMHD data can be sensitive to the electron temperature prescription, as was investigated recently by Anantua et al (2020) with a wide parameter space in their "critical beta" electron temperature model and equipartition-based constant electron beta/magnetic bias models.…”

Comparison of the ion-to-electron temperature ratio prescription: GRMHD simulations with electron thermodynamics

“…This ion-to-electron temperature ratio prescription has been used in the development of theoretical model observations in the image library of M87 by the EHT (Event Horizon Telescope Collaboration et al 2019e). Anantua et al (2020) have proposed several new parameterised prescriptions as a function of the plasma beta or the magnetic pressure, which are termed: critical beta electron temperature model, constant electron beta model, and magnetic bias model. Typically, a high ion-to-electron temperature ratio implies that the electron heating does not impact the dynamics of the plasma flows because the electron pressure is low.…”

GRMHD Simulations and Modeling for Jet Formation and Acceleration Region in AGNs

“…This temperature prescription leads to a hotter electron temperature within more magnetized regions, i.e., jet regions, helping to produce the observed flat radio spectra and making the jet more prominent compared to the accretion disk. Other parametrized prescriptions for the electron temperature are proposed in other studies [183,188,190,191] which are based on energy balance arguments and the properties at larger radii. Models inspired by the results of electron thermodynamics in GRMHD simulations have also been considered in recent years (e.g., [192,193]).…”