Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: GeV Gamma-ray Emission and Molecular Clouds towards Supernova Remnant
  G35.6$-$0.4 and the TeV Source HESS J1858+020   It is difficult to distinguish hadronic process from the leptonic one in
$\gamma$-ray observation, which is however crucial in revealing the origin of
cosmic rays. As an endeavor in the regard, we focus in this work on the complex
$\gamma$-ray emitting region, which partially overlaps with the unidentified
TeV source HESS~J1858+020 and includes supernova remnant (SNR) G35.6$-$0.4 and
HII region G35.6$-$0.5. We reanalyze CO-line, HI, and Fermi-LAT GeV
$\gamma$-ray emission data of this region. The analysis of the molecular and HI
data suggests that SNR G35.6$-$0.4 and HII region G35.6$-$0.5 are located at
different distances. The analysis the GeV $\gamma$-rays shows that GeV emission
arises from two point sources: one (SrcA) coincident with the SNR, and the
other (SrcB) coincident with both HESS J1858+020 and HII region G35.6$-$0.5.
The GeV emission of SrcA can be explained by the hadronic process in the SNR-MC
association scenario. The GeV-band spectrum of SrcB and the TeV-band spectrum
of HESS J1858+020 can be smoothly connected by a power-law function, with an
index of $\sim$2.2. The connected spectrum is well explained with a hadronic
emission, with the cutoff energy of protons above 1 PeV. It thus indicates that
there is a potential PeVatron in the HII region and should be further verified
with ultra-high energy observations with, e.g., LHAASO.

33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
23
The categories of this paper are: solv-int
3
The categories of this paper are: physics
11
The categories of this paper are: hep-lat
21
The categories of this paper are: adap-org
26
The categories of this paper are: bayes-an