2016A&A...596A..55Z


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.12CEST08:41:02

2016A&A...596A..55Z - Astronomy and Astrophysics, volume 596A, 55-55 (2016/12-1)

Gamma rays detected from Cygnus X-1 with likely jet origin.

ZANIN R., FERNANDEZ-BARRAL A., DE ONA WILHELMI E., AHARONIAN F., BLANCH O., BOSCH-RAMON V. and GALINDO D.

Abstract (from CDS):

Aims. We probe the high-energy (>60 MeV) emission from the black hole X-ray binary system, Cygnus X-1, and investigate its origin.
Methods. We analyzed 7.5yr of data by Fermi-LAT with the latest Pass 8 software version.
Results. We report the detection of a signal at ∼8σ statistical significance that is spatially coincident with Cygnus X-1 and has a luminosity of 5.5x1033erg/s, above 60MeV. 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 ∼20GeV without any sign of spectral break, is well fit by a power-law function with a photon index of 2.3±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 indicates the anisotropic inverse-Compton on stellar photons as the mechanism at work, thus constraining the emission region to a distance 1011-1013cm from the black hole.

Abstract Copyright: © ESO, 2016

Journal keyword(s): accretion, accretion disks - acceleration of particles - gamma rays: general - radiation mechanisms: non-thermal - stars: individual: Cygnus X-1 - X-rays: binaries

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2020.07.12-08:41:02

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