Post-adiabatic supernova remnants in an interstellar magnetic field: parallel and perpendicular shocks

Gamma-rays from hadronic collisions are expected from supernova remnants (SNRs) located near molecular clouds. The temperature of the shock interacting with the dense environment quickly reaches 10(5) K. Radiative losses of plasma become essential in the evolution of SNRs. They decrease the thermal pressure and essentially increase the density behind the shock. The presence of an ambient magnetic field may alter the behaviour of the post-adiabatic SNRs considerably compared with the hydrodynamic scenario. In the present article, magnetohy-drodynamic simulations of radiative shocks in a magnetic field are performed. High plasma compression due to radiative losses also results in a prominent increase in the strength of the tangential component of magnetic field behind the shock and a decrease of the parallel one. If the strength of the tangential field before the shock is higher than about 3 mu G, it prevents formation of a very dense thin shell. The higher the strength of the tangential magnetic field, the larger the thickness and the lower the maximum density in the radiative shell. The parallel magnetic field does not affect the distribution of the hydrodynamic parameters behind the shock. There are almost independent channels of energy transformations: radiative losses are due to thermal energy, magnetic energy increases come from reducing the kinetic energy. The large density and high strength of the perpendicular magnetic field in the radiative shells of SNRs should result in a considerable increase of the hadronic gamma-ray flux compared with the leptonic one.