Detection of high-energy gamma rays from Cygnus X-1 associated with the jets

Abstract

Cygnus X1 is the prototype black hole high-mass microquasar. As a persistent and bright X-ray source is considered an optimal candidate to study the disk-jet coupling. It displays the typical soft and hard X-ray spectral states of black hole binaries where the emission is dominated by the thermal black body radiation and by non-thermal emission from the inner part of the disk and the relativistic jets, respectively. We report the detection of a 8-sigma excess, above 60 MeV, spatially coincident with Cygnus X-1 by using 7.5 yr of Fermi-LAT data and the latest Pass8 software version. The point-like signal is clearly associated to the microquasar since the emission correlates with the hard X-ray state. In addition, there is a hint of orbital flux variability with most of the emission coming around the superior conjunction. The high energy emission is most likely associated with the jets and produced via anisotropic inverse Compton scattering on the stellar photons. The subsequent constraints on the emission regions are derived to a distance 1011 − 1013 cm from the black hole. All the results presented here have been published in [1].