Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: An updated estimate of the cosmic radio background and implications for
  ultra-high-energy photon propagation
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
15
The categories of this paper are: nucl-ex
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin