  Radiative magnetohydrodynamic simulation includes sufficiently realistic
physics to allow for the synthesis of remote sensing observables that can be
quantitatively compared with observations. We analyze the largest flare in a
simulation of the emergence of large flare-productive active regions described
by Chen et al. The flare releases $4.5\times10^{31}$ erg of magnetic energy and
is accompanied by a spectacular coronal mass ejection. Synthetic soft X-ray
flux of this flare reaches M2 class. The eruption reproduces many key features
of observed solar eruptions. A pre-existing magnetic flux rope is formed along
the highly sheared polarity inversion line between a sunspot pair and is
covered by an overlying multi-pole magnetic field. During the eruption, the
progenitor flux rope actively reconnects with the canopy field and evolves to
the large-scale multi-thermal flux rope that is observed in the corona.
Meanwhile, the magnetic energy released via reconnection is channeled down to
the lower atmosphere and gives rise to bright soft X-ray post-flare loops and
flare ribbons that reproduce the morphology and dynamic evolution of observed
flares. The model helps to shed light on questions of where and when the a flux
rope may form and how the magnetic structures in an eruption are related to
observable emission properties.
