Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photons in the science of the Pierre Auger Observatory   In this paper, the connection between Pierre Auger Observatory measurements
and photons is discussed. Three cases are presented: the search for photons in
the ultrahigh-energy cosmic-ray radiation, the impact of the photon background
in the cosmic ray propagation and the role of the ambient photon fields
surrounding cosmic accelerators.

30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
4
The categories of this paper are: cond-mat
24
The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph