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

• Published in: The Astrophysical journal 2019-05, Vol.876 (1), p.37
• Main Authors: Sano, H., Rowell, G., Reynoso, E. M., Jung-Richardt, I., Yamane, Y., Nagaya, T., Yoshiike, S., Hayashi, K., Torii, K., Maxted, N., Mitsuishi, I., Inoue, T., Inutsuka, S., Yamamoto, H., Tachihara, K., Fukui, Y.
• Format: Article
• Language: English
• Subjects: Acceleration; Astrophysics; Continuum radiation; Correlation; Cosmic rays; Elastic scattering; Gamma rays; gamma rays: ISM; Gas density; Interstellar chemistry; Interstellar gas; ISM: clouds; ISM: individual objects (RCW 86); ISM: supernova remnants; Magnetic fields; Molecular clouds; Protons; Radiation; Supernova; Supernova remnants; Supernovae; Synchrotron radiation
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab108f

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 predominantly 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 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 contribute alongside the 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, ∼1048-1049 erg, gives a safe lower limit due mainly to the low filling factor of interstellar gas within the shell.