Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gamma ray flares from Mrk421 in 2008 observed with the ARGO-YBJ detector   In 2008 the blazar Markarian 421 entered a very active phase and was one of
the brightest sources in the sky at TeV energies, showing frequent flaring
episodes. Using the data of ARGO-YBJ, a full coverage air shower detector
located at Yangbajing (4300 m a.s.l., Tibet, China), we monitored the source at
gamma ray energies E > 0.3 TeV during the whole year. The observed flux was
variable, with the strongest flares in March and June, in correlation with
X-ray enhanced activity. While during specific episodes the TeV flux could be
several times larger than the Crab Nebula one, the average emission from day 41
to 180 was almost twice the Crab level, with an integral flux of (3.6 +-0.6)
10^-11 photons cm^-2 s^-1 for energies E > 1 TeV, and decreased afterwards.
  This paper concentrates on the flares occurred in the first half of June.
This period has been deeply studied from optical to 100 MeV gamma rays, and
partially up to TeV energies, since the moonlight hampered the Cherenkov
telescope observations during the most intense part of the emission. Our data
complete these observations, with the detection of a signal with a statistical
significance of 3.8 standard deviations on June 11-13, corresponding to a gamma
ray flux about 6 times larger than the Crab one above 1 TeV. The reconstructed
differential spectrum, corrected for the intergalactic absorption, can be
represented by a power law with an index alpha = -2.1 extending up to several
TeV. The spectrum slope is fully consistent with previous observations
reporting a correlation between the flux and the spectral index, suggesting
that this property is maintained in different epochs and characterizes the
source emission processes.

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The categories of this paper are: atom-ph
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The categories of this paper are: supr-con
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
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The categories of this paper are: acc-phys
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-bio
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The categories of this paper are: hep-th
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The categories of this paper are: quant-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: econ
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn