Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Search for extended gamma ray emission in Markarian 421 using VERITAS
  observations   Very high energy (VHE: >100 GeV) gamma rays coming from AGN can pair-produce
on the intergalactic background light generating an electromagnetic cascade. If
the Intergalactic Magnetic Field (IGMF) is sufficiently strong, this cascade
may result in an extended isotropic emission of photons around the source, or
halo. Using VERITAS observations of the blazar Markarian 421, we search for
extended emission by comparing the source angular distribution (${\theta}^2$)
from a quiescent period with one coming from a flare period, which can be
considered as halo-free. ${\chi}^2$ test showed no significant statistical
differences between the samples, suggesting that the effect is either
non-existent or too weak to be detected. We calculated upper limits for the
extended flux considering different angle ranges, the most stringent being <8%
of the Crab Nebulae flux (C.U), in the range $0\deg \leq {\theta} \leq 0.1\deg$ .

15
The categories of this paper are: nucl-ex
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
11
The categories of this paper are: hep-lat
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
2
The categories of this paper are: math
26
The categories of this paper are: bayes-an
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The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg