Simulating TeV gamma-ray morphologies of shell-type supernova remnants
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY(2020)
摘要
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.
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关键词
MHD,shock waves,cosmic rays,ISM: supernova remnants,gamma rays: ISM
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