Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Point-like gamma ray sources as signatures of distant accelerators of
  ultra high energy cosmic rays   We discuss the possibility of observing distant accelerators of ultra high
energy cosmic rays in synchrotron gamma rays. Protons propagating away from
their acceleration sites produce extremely energetic electrons during
photo-pion interactions with cosmic microwave background photons. If the
accelerator is embedded in a magnetized region, these electrons will emit high
energy synchrotron radiation. The resulting synchrotron source is expected to
be point-like and detectable in the GeV-TeV energy range if the magnetic field
is at the nanoGauss level.

4
The categories of this paper are: cond-mat
7
The categories of this paper are: hep-th
17
The categories of this paper are: q-fin
3
The categories of this paper are: physics
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
1
The categories of this paper are: cs
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph