Effects of Leakage Neutral Particles on Shocks

TL;DR

This study examines how leakage neutral particles influence shock structures in partially ionized media, revealing their role in modifying shock compression, magnetic field amplification, and gamma-ray spectra in supernova remnants.

Contribution

The paper provides analytical solutions for the precursor structure caused by leakage neutral particles and demonstrates their impact on shock dynamics and particle acceleration.

Findings

Leakage neutral particles constitute about 10% of upstream neutrals at certain shock velocities.

Leakage neutral particles reduce the shock compression ratio but do not affect the total compression ratio.

Leakage neutral particles can amplify magnetic fields and heat the upstream region.

Abstract

In this paper we investigate effects of neutral particles on shocks propagating into the partially ionized medium. We find that for 120 km/s < u_{sh} < 3000 km/s (u_{sh} is the shock velocity), about ten percent of upstream neutral particles leak into the upstream region from the downstream region. Moreover, we investigate how the leakage neutral particles affect the upstream structure of the shock and particle accelerations. Using four fluid approximations (upstream ions, upstream neutral particles, leakage neutral particles and pickup ions), we provide analytical solutions of the precursor structure due to leakage neutral particles. It is shown that the upstream flow is decelerated in the precursor region and the shock compression ratio becomes smaller than without leakage neutral particles, but the total compression ratio does not change. Even if leakage of neutral particles is small (a few percents of total upstream particles), this smaller compression ratio of the shock can explain steep gamma-ray spectra from young supernova remnants. Furthermore, leakage neutral particles could amplify the magnetic field and heat the upstream region.