Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Redshifts of distant blazar limited by Fermi and VHE $\gamma$-ray
  observations   Our goal is to limit the redshifts of three blazars PG 1553+113, 3C 66A and
PKS 1424+240, through the investigation of their Fermi and VHE (very high
energy) $\gamma$-ray observations. We assume that the intrinsic spectra of PG
1553+113, 3C 66A, and PKS 1424+240 have not any cutoff across the Fermi and VHE
$\gamma$-ray energy ranges. The intrinsic spectra of VHE $\gamma$-rays are
obtained through the extrapolation of Fermi spectra. Comparing the measured and
intrinsic VHE spectra due to extragalactic background light (EBL) absorption,
we give the redshift upper limits of three blazars assuming a specific EBL
model. The redshift upper limits of PG 1553+113, 3C 66A and PKS 1424+240 are
0.78, 0.58, and 1.19 respectively. Near the TeV energy the optical depth of VHE
$\gamma$ photons might be overestimated by Franceschini (2008) EBL model, or
the second emission component might be present in the VHE spectra and lead the
intrinsic photon index harder than the Fermi ones.

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The categories of this paper are: q-alg
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The categories of this paper are: hep-ex
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The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: econ
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The categories of this paper are: supr-con
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The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-ex
2
The categories of this paper are: math
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The categories of this paper are: q-fin
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The categories of this paper are: adap-org
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The categories of this paper are: solv-int
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The categories of this paper are: q-bio