Efficient cosmic ray acceleration, hydrodynamics, and Self-consistent Thermal X-ray Emission applied to SNR RX J1713.7-3946

TL;DR

This study models the combined thermal and non-thermal emission from SNR RX J1713.7-3946, constraining ambient medium density and electron-proton ratios, and favoring leptonic over hadronic emission processes based on Suzaku X-ray data.

Contribution

It introduces a self-consistent model that simultaneously predicts thermal X-ray and non-thermal emission in SNRs, incorporating plasma ionization and electron heating mechanisms.

Findings

Thermal X-ray line emission is more luminous than bremsstrahlung continuum.

Suzaku observations constrain ambient density and electron-proton ratios.

Leptonic models better fit the broad-band emission data.

Abstract

We model the broad-band emission from SNR RX J1713.7-3946 including, for the first time, a consistent calculation of thermal X-ray emission together with non-thermal emission in a nonlinear diffusive shock acceleration (DSA) model. Our model tracks the evolution of the SNR including the plasma ionization state between the forward shock and the contact discontinuity. We use a plasma emissivity code to predict the thermal X-ray emission spectrum assuming the initially cold electrons are heated either by Coulomb collisions with the shock heated protons (the slowest possible heating), or come into instant equilibration with the protons. For either electron heating model, electrons reach >10^7 K rapidly and the X-ray line emission near 1 keV is more than 10 times as luminous as the underlying thermal bremsstrahlung continuum. Since recent Suzaku observations show no detectable line emission, this places strong constraints on the unshocked ambient medium density and on the relativistic electron to proton ratio. For the uniform circumstellar medium (CSM) models we consider, the low densities and high relativistic electron to proton ratios required to match the Suzaku X-ray observations definitively rule out pion-decay as the emission process producing GeV-TeV photons. We show that leptonic models, where inverse-Compton scattering against the cosmic background radiation dominates the GeV-TeV emission, produce better fits to the broad-band thermal and non-thermal observations in a uniform CSM.