Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of an energetic radiation burst from mountain-top
  thunderclouds   During thunderstorms on 2008 September 20, a simultaneous detection of gamma
rays and electrons was made at a mountain observatory in Japan located 2770 m
above sea level. Both emissions, lasting 90 seconds, were associated with
thunderclouds rather than lightning. The photon spectrum, extending to 10 MeV,
can be interpreted as consisting of bremsstrahlung gamma rays arriving from a
source which is 60 - 130 m in distance at 90% confidence level. The observed
electrons are likely to be dominated by a primary population escaping from an
acceleration region in the clouds.

16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
0
The categories of this paper are: hep-ph
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
33
The categories of this paper are: plasm-ph