Simulating TeV gamma-ray morphologies of shell-type supernova remnants

Supernova remnant (SNR) shocks provide favourable sites of cosmic ray (CR) proton acceleration if the local magnetic field direction is quasi-parallel to the shock normal. Using the moving-mesh magnetohydrodynamical (MHD) code AREPO we present a suite of SNR simulations with CR acceleration in the Sedov-Taylor phase that combine different magnetic field topologies, density distributions with gradients and large-scale fluctuations, and - for our core-collapse SNRs - a multiphase interstellar medium with dense clumps with a contrast of 10(4). Assuming the hadronic gamma-ray emission model for the TeV gamma-ray emission, we find that large-amplitude density fluctuations of delta rho/rho(0) greater than or similar to 75 per cent are required to strongly modulate the gammaray emissivity in a straw man's model in which the acceleration efficiency is independent of magnetic obliquity. However, this causes strong corrugations of the shock surface that are ruled out by gamma-ray observations. By contrast, magnetic obliquitydependent acceleration can easily explain the observed variance in gamma-ray morphologies ranging from SN1006 (with a homogeneous magnetic field) to Vela Junior and RX J1713 (with a turbulent field) in a single model that derives from plasma particle-in-cell simulations. Our best-fitting model for SN1006 has a large-scale density gradient of del n similar or equal to 0.0034 cm(-3) pc(-1) pointing from south-west to north-east and a magnetic inclination with the plane of the sky of less than or similar to 10 degrees. Our best-fitting model for Vela Junior and RX J1713 adopts a combination of turbulent magnetic field and dense clumps to explain their TeV gamma-ray morphologies and moderate shock corrugations.