Study of the effect of turbulent interstellar medium on the morphology of young supernova remnants

Abstract

Context. Supernova remnants (SNRs) are one of the main sources of galactic cosmic-ray acceleration. This acceleration, believed to happen at the blast wave front, leads to energy loss at the shock front. This results in the apparent proximity between the blast wave and the contact discontinuity. Aims. In this article, we study the effect that turbulent-like density perturbations of the interstellar medium (ISM) have on the evolution of young SNRs. We focus on the impact these fluctuations have on the structure of SNRs and more precisely on the resulting distance between blast wave and contact discontinuity. As cosmic-ray acceleration is necessary to explain this distance, this study indirectly puts into question the cosmic-ray acceleration at the blast wave front. Methods. We performed a set of purely hydrodynamic three-dimensional simulations without cosmic-ray acceleration in a co-expanding frame. We randomly initialised the density variation of the ISM following a Kolmogorov power law. The resulting ratios of radii between blast wave, contact discontinuity, and reverse shock are then compared to astronomical observations. Results. The addition of density perturbation does not significantly change the average ratio of radii. However, the simulations show a higher growth of interfacial instabilities in the presence of a turbulent ISM. The resulting deformation of the contact discontinuity could explain the proximity between contact discontinuity and blast wave. The deformations also explain the plateau in the radial distribution of the line-of-sight velocity associated with the observations of Tycho. Conclusions. Density perturbations of the ISM should not be neglected in the simulation of young SNRs as they have an impact on the structure of these latter objects that is comparable to that of cosmic-ray acceleration.