Nonthermal Radiation from Supernova Remnants: Effects of Magnetic Field Amplification and Particle Escape

TL;DR

This paper investigates how magnetic field amplification and particle escape influence cosmic ray acceleration and nonthermal emissions in supernova remnants, highlighting the challenges in modeling PeV protons and their observational signatures.

Contribution

It introduces a nonlinear DSA model incorporating magnetic field amplification, Alfv'enic drift, and particle escape, providing insights into their combined effects on cosmic ray spectra and emissions.

Findings

PeV protons require extensive amplified magnetic regions.

Achieving 10% energy conversion to CRs with steep spectra is challenging.

Nonthermal spectra depend on shock evolution, magnetic amplification, and particle escape.

Abstract

We explore nonlinear effects of wave-particle interactions on the diffusive shock acceleration (DSA) process in Type Ia-like, SNR blast waves, by implementing phenomenological models for magnetic field amplification, Alfv'enic drift, and particle escape in time-dependent numerical simulations of nonlinear DSA. For typical SNR parameters the CR protons can be accelerated to PeV energies only if the region of amplified field ahead of the shock is extensive enough to contain the diffusion lengths of the particles of interest. Even with the help of Alfv'enic drift, it remains somewhat challenging to construct a nonlinear DSA model for SNRs in which order of 10 % of the supernova explosion energy is converted to the CR energy and the magnetic field is amplified by a factor of 10 or so in the shock precursor, while, at the same time, the energy spectrum of PeV protons is steeper than E^{-2}. To explore the influence of these physical effects on observed SNR emissions, we also compute resulting radio-to-gamma-ray spectra. Nonthermal emission spectra, especially in X-ray and gamma-ray bands,depend on the time dependent evolution of CR injection process, magnetic field amplification, and particle escape, as well as the shock dynamic evolution. This result comes from the fact that the high energy end of the CR spectrum is composed of the particles that are injected in the very early stages of blast wave evolution. Thus it is crucial to understand better the plasma wave-particle interactions associated with collisionless shocks in detail modeling of nonthermal radiation from SNRs.