Gamma-rays from anisotropic IC e^{\pm} pair cascades in microquasars: Application to Cyg X-3

TL;DR

This paper models gamma-ray emission in microquasars like Cyg X-3, showing how anisotropic inverse Compton pair cascades in jets produce angle-dependent spectra that match observations.

Contribution

It introduces a detailed model of gamma-ray production via anisotropic IC pair cascades in microquasar jets, accounting for observational angle effects and applying it to Cyg X-3.

Findings

Gamma-ray spectra depend strongly on observation angle.

Electron injection in the inner jet region explains observed spectra.

Model successfully reproduces Cyg X-3 gamma-ray observations.

Abstract

Microquasars have been expected to emit high energy gamma-rays due to their general similarities to the gamma-ray emitting blazars (evidences of relativistic jets, non-thermal radio to X-ray emission). In fact, the first source of this type, Cyg X-3, has been recently unambiguously discovered by the satellite telescopes. We study the features of the gamma-ray radiation produced in these sources by relativistic electrons, accelerated in the inner part of the jet. The electrons initiate an Inverse Compton e^\pm pair cascade in the radiation field of the accretion disk. Due to the anisotropy of the accretion disk radiation field, the spectra of gamma-rays show strong dependence on the observation angle, the location of the emission region within the jet and the details of the acceleration process. As an example, we confront our model with the observations of the microquasar Cyg X-3, which has been recently reported as a transient GeV gamma-ray source by the Agile and the Fermi Observatories. Satisfactory description of the gamma-ray spectra observed from Cyg X-3 are obtained in the case of the injection of electrons in the inner part of the jet (located within 300 inner disk radius from the jet base) provided that the observer is located at relatively small angle to the jet axis.