Possible Evidence for Cosmic-Ray Acceleration in the Type Ia SNR RCW 86: Spatial Correlation between TeV Gamma rays and Interstellar Atomic Protons

TL;DR

This study provides evidence that TeV gamma rays in the Type Ia SNR RCW 86 are mainly of hadronic origin, with spatial correlations indicating cosmic-ray acceleration and interactions with interstellar gas, and suggests both core-collapse and Type Ia supernovae can accelerate cosmic rays.

Contribution

It offers detailed morphological analysis linking gamma-ray emission to interstellar gas, highlighting the role of magnetic turbulence and mixed leptonic-hadronic processes in cosmic-ray acceleration in RCW 86.

Findings

Gamma rays correlate with atomic gas, indicating hadronic origin.

Poor correlation with molecular clouds due to magnetic turbulence.

Leptonic processes may contribute to gamma-ray emission.

Abstract

We present a detailed morphological study of TeV gamma rays, synchrotron radiation, and interstellar gas in the young Type Ia supernova remnant (SNR) RCW 86. We find that the interstellar atomic gas shows good spatial correlation with the gamma rays, indicating that the TeV gamma rays from RCW 86 are likely to be dominantly of hadronic origin. In contrast, the spatial correlation between the interstellar molecular cloud and the TeV gamma rays is poor in the southeastern shell of the SNR. We argue that this poor correlation can be attributed to the low-energy cosmic rays (~ 1 TeV) not penetrating into the dense molecular cloud due to an enhancement of the turbulent magnetic field around the dense cloud of ~ 10-100 $\mu$G. We also find that the southwestern shell, which is bright in both synchrotron X-ray and radio continuum radiation, shows a significant gamma-ray excess compared with the interstellar proton column density, suggesting that leptonic gamma rays via inverse Compton scattering possibly contributes along with hadronic gamma rays. The total cosmic-ray energies of the young TeV gamma-ray SNRs$-$RX J1713.7$-$3946, Vela Jr, HESS J1731$-$347, and RCW 86$-$are roughly similar, which indicates that cosmic rays can be accelerated in both the core-collapse and Type Ia supernovae. The total energy of cosmic rays derived using the gas density, ~ 10$^{48}$-10$^{49}$ erg, gives a safe lower limit due mainly to the low filling factor of interstellar gas within the shell.