Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the significance of the observed clustering of ultra-high energy
  cosmic rays   Three pairs of possibly correlated ultra-high energy cosmic ray events were
reported by Hayashida et al (1996). Here we calculate the propagation of the
corresponding particles through both the intergalactic and galactic magnetic
fields. The large scale disc and halo magnetic components are approximated by
the models of Stanev (1997). The intergalactic magnetic field intensity is
modulated by the actual density of luminous matter along the corresponding
lines of sight, calculated from the CfA redshift catalogue (Huchra et al,
1995). The results indicate that, if the events of each pair had a common
source and were simultaneously produced, they either originated inside the
galactic halo or otherwise very unlikely events were observed. On the other
hand, an estimate of the arrival probability of ultra-high energy cosmic rays,
under the assumption that the distribution of luminous matter in the nearby
universe traces the distribution of the sources of the particles and intensity
of the intergalactic magnetic field, suggests that the pairs are chance
clusterings.

33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex