Origin of Multi-Band Emission From the Microquasar Cygnus X-1

Abstract

We study the origin of non-thermal emissions from the Galactic black hole X-ray binary Cygnus X-1 which is a confirmed high mass microquasar. By analogy with those methods used in studies of active galactic nuclei, we propose a two-dimensional, time-dependent radiation model from the microquasar Cygnus X-1. In this model, the evolution equation for relativistic electrons in a conical jet are numerically solved by including escape, adiabatic and various radiative losses. The radiative processes involved are synchrotron emission, its self-Compton scattering, and inverse Compton scatterings of an accretion disk and its surrounding stellar companion. This model also includes an electromagnetic cascade process of an anisotropic γ-γ interaction. We study the spectral properties of electron evolution and its emission spectral characteristic at different heights of the emission region located in the jet. We find that radio data from Cygnus X-1 are reproduced by the synchrotron emission, the Fermi LAT measurements by the synchrotron emission and Comptonization of photons of the stellar companion, the TeV band emission fluxes by the Comptonization of the stellar photons. Our results show that: (1) Radio emission region extends from the binary system scales to the termination of the jet. (2) The GeV band emissions should originate from the distance close to the binary system scales. (3) The TeV band emissions could be inside the binary system, and these emissions could be probed by the upcoming CTA telescope. (4) The MeV tail emissions, which produces a strongly linearly polarized signal, are emitted inside the binary system. The location of the emissions is very close to the inner region of the jet.

Polarization Radiation with Turbulent Magnetic Fields from X-Ray Binaries

“…Regarding numerical procedures to solve Equation (2), interested readers are referred to Zhang et al (2014), in which we have studied in detail the evolution of relativistic electrons along the jet. The model parameters are: the starting point of the dissipation region z 0 ; the terminal position of the dissipation region z max ; the spectral index of relativistic electrons p; the break energy of electrons γ cut ; the minimum Lorentz factor of electrons γ min ; the characteristic length of turbulence λ; the angle ϕ between the normal to the slab and the line of sight, and the magnetic field strength B ls,0 .…”

“…The parameters related to the companion star are its effective surface temperature of ∼ 2.8 × 10 4 K, and its radius of 16R ⊙ , which immediately gives the monochromatic luminosity ∼ 10 38 erg s −1 , according to the Stefan-Boltzmann law. The parameters related to the jet are the bulk Lorentz factor of Γ j = 1.25 (Zdziarski et al 2014a;Zhang et al 2014;Zdziarski et al 2016), and the half-opening angle of the jet of 0.5…”

“…The fitting procedures used above are similar to those presented in Zhang et al (2014), in which we have studied the origin of multiband emission in a certain region of the jet. Here, we simply express the motivations for the parameter choice.…”

“…Here, we simply express the motivations for the parameter choice. Based on the studies in Zhang et al (2014), in which the MeV tail emissions are produced inside the binary system and the GeV band emissions are from the distance close to the binary system scales, we thus fix z max = R orb (see Figure 5) and 15R orb (see Figure 6) for fitting MeV tail plus Fermi LAT data and for only Fermi LAT data, respectively. Then, we adjust magnetic field strength B ls,0 and z min to calculate radiative fluxes due to jitter, synchrotron and IC scattering processes.…”

“…In this work, we neglect synchrotron self-Compton scattering and Comptonization of the photons from accretion disk and corona components, on the basis of the studies of Zhang et al (2014). The second term of the right-hand side of Equation (3) indicates the adiabatic loss of relativistic electrons due to an adiabatically expanding jet.…”