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arXiv · 1801.07881

Evidence for a neutral iron line generated by MeV protons from supernova remnants interacting with molecular clouds

Kumiko K. Nobukawa·Masayoshi Nobukawa·Katsuji Koyama·Shigeo Yamauchi·Hideki Uchiyama·Hiromichi Okon·Takaaki Tanaka·Hiroyuki Uchida·Takeshi G. Tsuru
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Abstract

Supernova remnants (SNRs) have been prime candidates for Galactic cosmic-ray accelerators. When low-energy cosmic-ray protons (LECRp) collide with interstellar gas, they ionize neutral iron atoms and emit the neutral iron line (Fe I K$α$) at 6.40keV. We search for the iron K-shell line in seven SNRs from the Suzaku archive data of the Galactic plane in the $6^{\circ} \lesssim l \lesssim 40^{\circ}, |b| < 1^{\circ}$ region. All these SNRs interact with molecular clouds. We discover Fe I K$α$ line emissions from five SNRs (W28, Kes 67, Kes 69, Kes 78, and W44). The spectra and morphologies suggest that the Fe I K$α$ line is produced by interactions between LECRp and the adjacent cold gas. The proton energy density is estimated to be $\gtrsim$ 10-100 eV cm$^{-3}$, which is more than 10 times higher than that in the ambient interstellar medium.

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Kumiko K. Nobukawa, Masayoshi Nobukawa, Katsuji Koyama, Shigeo Yamauchi, Hideki Uchiyama, Hiromichi Okon, Takaaki Tanaka, Hiroyuki Uchida, Takeshi G. Tsuru. 2018-01-24. Evidence for a neutral iron line generated by MeV protons from supernova remnants interacting with molecular clouds. https://doi.org/10.3847/1538-4357%2Faaa8dc

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