Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Detection of gamma rays of likely jet origin in Cygnus X-1   Aims: Probe the high-energy ($>$60 MeV) emission from the black hole X-ray
binary system, Cygnus X-1, and investigate its origin. Methods: We analysed 7.5
yr of data by Fermi/LAT with the latest PASS8 software version. Results: We
report the detection of a signal at $\sim$8 $\sigma$ statistical significance
spatially coincident with Cygnus X-1 and a luminosity above 60 MeV of
5.5$\times$10$^{33}$ erg s$^{-1}$. The signal is correlated with the hard X-ray
flux: the source is observed at high energies only during the hard X-ray
spectral state, when the source is known to display persistent, relativistic
radio emitting jets. The energy spectrum, extending up to $\sim$20 GeV without
any sign of spectral break, is well fitted by a power-law function with a
photon index of 2.3$\pm$0.2. There is a hint of orbital flux variability, with
high-energy emission mostly coming around the superior conjunction.
Conclusions: We detected GeV emission from Cygnus X-1 and probed that the
emission is most likely associated with the relativistic jets. The evidence of
flux orbital variability points to the anisotropic inverse Compton on stellar
photons as the mechanism at work, thus constraining the emission region to a
distance $10^{11}-10^{13}$ cm from the black hole.

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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
26
The categories of this paper are: bayes-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: physics
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The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
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The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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The categories of this paper are: eess