  In the vicinity of black holes, the influence of strong gravity, plasma
physics, and emission processes govern the behavior of the system. Since
observations such as those carried out by the EHT are not yet able to
unambiguously constrain models for astrophysical and gravitational properties,
it is imperative to explore the accretion models, particle distribution
function, and description of the spacetime geometry. Our current understanding
of these properties is often based on the assumption that the spacetime is
well-described by by the Kerr solution to general relativity, combined with
basic emission and accretion models. We explore alternative models for each
property performing general relativistic magnetohydrodynamic and radiative
transfer simulations. By choosing a Kerr solution to general relativity and a
dilaton solution to Einstein-Maxwell-dilaton-axion gravity as exemplary black
hole background spacetimes, we aim to investigate the influence of accretion
and emission models on the ability to distinguish black holes in two theories
of gravity.
  We carry out three-dimensional general relativistic magnetohydrodynamics
simulations of both black holes, matched at their innermost stable circular
orbit, in two distinct accretion scenarios. Using general-relativistic
radiative transfer calculations, we model the thermal synchrotron emission and
in the next step apply a non-thermal electron distribution function, exploring
representative parameters to compare with multiwavelength observations. We
further consider Kerr and dilaton black holes matched at their unstable
circular photon orbits, as well as their event horizons.
  From multiwavelength emission and spectral index analysis, we find that
accretion model and spacetime have only a small impact on the spectra compared
to the choice of emission model.
