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Title: Gamma rays detected from Cygnus X-1 with likely jet origin
Author: Zanin, Roberta
Fernández-Barral, Alba
Oña-Wilhelmi, Emma de
Aharonian, Felix
Blanch, Oscar
Bosch i Ramon, Valentí
Galindo Fernández, Daniel
Keywords: Raigs gamma
Forats negres (Astronomia)
Gamma rays
Black holes (Astronomy)
Issue Date: 29-Nov-2016
Publisher: EDP Sciences
Abstract: 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 7.5 yr 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 5.5 × 1033 erg s-1, above 60 MeV. 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 ~20 GeV 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 1011-1013 cm from the black hole.
Note: Reproducció del document publicat a:
It is part of: Astronomy & Astrophysics, 2016, vol. 596, p. A55
Related resource:
ISSN: 0004-6361
Appears in Collections:Articles publicats en revistes (Institut de Ciències del Cosmos (ICCUB))
Articles publicats en revistes (Física Quàntica i Astrofísica)

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