Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Extragalactic Background Light: new constraints from the study of the
  photon-photon absorption on blazar spectra   The study of the Extragalactic Background Light (EBL) is crucial to
understand many astrophysical problems (as the formation of first stars, the
evolution of galaxies and the role of dust emission). At present, one of the
most powerful ways to put constraints on EBL is represented by the study of the
photon-photon absorption on gamma-ray spectra of TeV blazars. Adopting this
method, we found that, if the only contribution to the optical and Near
Infrared (NIR) background is given by galaxies, the spectrum of the blazar
H1426+428 cannot be fitted. To reproduce the observational data of H1426+428 a
Near Infrared excess with respect to galaxy counts is required, with amplitude
consistent with both the Matsumoto et al. (2000) data with Kelsall's model of
zodiacal light (ZL) subtraction and the DIRBE data with Wright's model of ZL
subtraction. The derived constraints on the optical EBL are weaker, because the
experimental errors on blazar data are still bigger than the differences among
various optical EBL models. In the mid-infrared the SPITZER measurement at 24
micron provides the best fit of the blazar spectrum.

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The categories of this paper are: physics
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The categories of this paper are: acc-phys
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The categories of this paper are: gr-qc
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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: atom-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: math-ph
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The categories of this paper are: solv-int
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The categories of this paper are: q-fin
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The categories of this paper are: patt-sol
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The categories of this paper are: math
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The categories of this paper are: nucl-th
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The categories of this paper are: cond-mat
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The categories of this paper are: q-bio
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The categories of this paper are: stat