Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evidence for a neutral iron line generated by MeV protons from supernova
  remnants interacting with molecular clouds   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$\alpha$) 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$\alpha$ line emissions from five SNRs
(W28, Kes 67, Kes 69, Kes 78, and W44). The spectra and morphologies suggest
that the Fe I K$\alpha$ 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.

21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph