  Supernova remnants are known to accelerate cosmic rays on account of their
non-thermal emission of radio waves, X-rays, and gamma rays. Although there are
many models for the acceleration of cosmic rays in Supernova remnants, the
escape of cosmic rays from these sources is yet understudied.
  We use our time-dependent acceleration code RATPaC to study the acceleration
of cosmic rays and their escape in post-adiabatic Supernova remnants and
calculate the subsequent gamma-ray emission from inverse-Compton scattering and
Pion decay.
  We performed spherically symmetric 1-D simulations in which we simultaneously
solve the transport equations for CRs, magnetic turbulence, and the
hydrodynamical flow of the thermal plasma in a volume large enough to keep all
CRs in the simulation. The transport equations for cosmic-rays and magnetic
turbulence are coupled via the cosmic-ray gradient and the spatial diffusion
coefficient of the cosmic rays, while the cosmic-ray feedback onto the shock
structure can be ignored. Our simulations span 100kyrs, thus covering the
remnants evolution until the beginning of the post-adiabatic phase.
  At later stages of the evolution cosmic rays over a wide range of energy can
reside outside of the remnant, creating spectra that are softer than predicted
by standard DSA and feature breaks in the 10-100 GeV-range. The total spectrum
of cosmic rays released into the interstellar medium has a spectral index of
s~2.4 above roughly 10 GeV which is close to that required by Galactic
propagation models. We further find the gamma-ray luminosity to peak around an
age of 4,000 years for inverse-Compton-dominated high-energy emission. Remnants
expanding in low-density media emit generally more inverse-Compton radiation
matching the fact that the brightest known supernova remnants - RCW86, Vela Jr,
HESSJ1731-347 and RXJ1713.7-3946 - are all expanding in low density
environments.
