Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cosmic rays and Radio Halos in galaxy clusters : new constraints from
  radio observations   Clusters of galaxies are sites of acceleration of charged particles and
sources of non-thermal radiation. We report on new constraints on the
population of cosmic rays in the Intra Cluster Medium (ICM) obtained via radio
observations of a fairly large sample of massive, X-ray luminous, galaxy
clusters in the redshift interval 0.2--0.4. The bulk of the observed galaxy
clusters does not show any hint of Mpc scale synchrotron radio emission at the
cluster center (Radio Halo). We obtained solid upper limits to the diffuse
radio emission and discuss their implications for the models for the origin of
Radio Halos. Our measurements allow us to derive also a limit to the content of
cosmic ray protons in the ICM. Assuming spectral indices of these protons delta
=2.1-2.4 and microG level magnetic fields, as from Rotation Measures, these
limits are one order of magnitude deeper than present EGRET upper limits, while
they are less stringent for steeper spectra and lower magnetic fields.

16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
29
The categories of this paper are: funct-an
19
The categories of this paper are: eess
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol