Using optical lines to study particle acceleration at supernova remnants

TL;DR

This paper explores how optical Balmer lines in supernova remnants can reveal details about particle acceleration and shock conditions, using kinetic theory and applying it to specific remnants to assess cosmic ray acceleration efficiency.

Contribution

It introduces a kinetic theory framework for analyzing Balmer line profiles to evaluate shock acceleration efficiency in young supernova remnants.

Findings

Anomalous Balmer lines indicate ~10% shock energy conversion to non-thermal particles in some SNRs.

Efficient cosmic ray acceleration is observed in RCW 86, SNR 0509-67.5, and Tycho.

No evidence of efficient acceleration in the northwestern part of SN 1006.

Abstract

The shocks of several young supernova remnants (SNR) are often associated with very thin optical filaments dominated by Balmer emission resulting from charge-exchange and collisional excitation between neutral Hydrogen from the interstellar medium and shocked protons and electrons. Optical lines are a direct probe of the conditions at the shock, in particular the width of the narrow and broad components reflect the temperature upstream and downstream of the shock, respectively. When the shock accelerate efficiently non-thermal particles, the shock structure changes producing anomalous Balmer lines and it is possible to use their line shape and their spatial profile to check the efficiency of SNR shocks in accelerating cosmic rays. Here we illustrate the kinetic theory of shock acceleration in presence of neutrals with some applications to young SNRs. We show that in three cases (RCW 86, SNR 0509-67.5 and Tycho) anomalous Balmer lines can be explained assuming that a fraction of $\sim 10\%$ of the total shock kinetic energy is converted into not thermal particles, while in one single case, the northwestern part of SN 1006, there is no evidence of efficient acceleration.