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

TL;DR

This paper uses advanced MHD simulations to explore how magnetic field topology and density fluctuations influence TeV gamma-ray morphologies of shell-type supernova remnants, providing models that match observations.

Contribution

It introduces a comprehensive simulation approach combining magnetic obliquity-dependent acceleration with complex ISM structures to explain gamma-ray morphologies.

Findings

Magnetic obliquity-dependent acceleration explains observed gamma-ray variance.

Large density fluctuations alone cause shock corrugations inconsistent with observations.

Turbulent magnetic fields and dense clumps are key to modeling Vela Junior and RX J1713.

Abstract

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 magneto-hydrodynamical (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 multi-phase 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 $\delta\rho/\rho_0\gtrsim75$ per cent are required to strongly modulate the gamma-ray 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 obliquity-dependent 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-fit model for SN1006 has a large-scale density gradient of $ \nabla{n}\simeq 0.0034~\mathrm{cm}^{-3}~\mathrm{pc}^{-1} $ pointing from south-west to north-east and a magnetic inclination with the plane of the sky of $\lesssim10^\circ$. Our best-fit 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.