  In spite of a large number of global three-dimensional (3D)
magneto-hydrodynamical (MHD) simulations of accretion flows and jets being made
recently, their astrophysical relevance for realistic situations is not well
known. In order to examine to what extent the simulated MHD flows can account
for the observed spectral energy distribution (SED) of Sagittarius A* (Sgr A*),
for the first time we calculate the emergent spectra from 3D MHD flows in a
wide range of wavelengths (from radio to X-ray) by solving the 3D radiative
transfer equations. We use the simulation data by Kato, Mineshige, and Shibata
(2004) and perform Monte Carlo radiative transfer simulations, in which
synchrotron emission/absorption, free-free emission/absorption, and
Compton/inverse Compton scattering are taken into account. We assume two
temperature plasmas and calculate electron temperatures by solving the electron
energy equation. Only thermal electrons are considered. It is found that the 3D
MHD flow generally over-produces X-rays by means of bremsstrahlung radiation
from the regions at large radii. A flatter density profile, r^{-a} with a<1,
than that of the advection-dominated accretion flow (ADAF), r^{-3/2}, is the
main reason for this. If we restrict the size of the emission region to be as
small as 10r_s, where r_s is the Schwarzschild radius, the MHD model can
reproduce the basic features of the observed SED of Sgr A* during its flaring
state. Yet, the spectrum in the quiescent state remains to be understood. We
also calculate the time-dependent spectral changes, finding that the fluxes
fluctuate in a wide range of the frequency and the flux at each wavelength does
not always vary coherently.
