Absorption of high-energy gamma rays in Cygnus X-3

Abstract

The microquasar Cygnus X-3 was detected at high energies by the gamma-ray space telescopes AGILE and Fermi. The gamma-ray emission is transient, modulated with the orbital period and seems related to major radio flares, i.e. to the relativistic jet. The GeV gamma-ray flux can be substantially attenuated by internal absorption with the ambient X-rays. In this study, we examine quantitatively the effect of pair production in Cygnus X-3 and put constraints on the location of the gamma-ray source. Cygnus X-3 exhibits complex temporal and spectral patterns in X-rays. During gamma-ray flares, the X-ray emission can be approximated by a bright disk black body component and a non-thermal tail extending in hard X-rays, possibly related to a corona above the disk. We calculate numerically the exact optical depth for gamma rays above a standard accretion disk. Emission and absorption in the corona are also investigated. GeV gamma rays are significantly absorbed by soft X-rays emitted from the inner parts of the accretion disk. The absorption pattern is complex and anisotropic. Isotropization of X-rays due to Thomson scattering in the companion star wind tends to increase the gamma-ray opacity. Gamma rays from the corona suffer from strong absorption by photons from the disk and cannot explain the observed high-energy emission, unless the corona is unrealistically extended. The lack of absorption feature in the GeV emission indicates that high-energy gamma rays should be located at a minimum distance ~10^8-10^10 cm from the compact object. The gamma-ray emission is unlikely to have a coronal origin.

11 pages, 9 figures, accepted for publication in Astronomy and Astrophysics

References in corpus (6)

• Physical Properties of Wolf-Rayet Stars
• Simulating radiation and kinetic processes in relativistic plasmas
• Effects of the stellar wind on X-ray spectra of Cygnus X-3
• Spectral variability in Cygnus X-3
• The nature of the hard state of Cygnus X-3
• The magnetic field and the location of the TeV emitter in Cygnus X-1 and LS 5039

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• The AGILE monitoring of Cygnus X-3: transient gamma-ray emission and spectral constraints
• A magnetic reconnection model for explaining the multi-wavelength emission of the microquasars Cyg X-1 and Cyg X-3
• Particle transport in magnetized media around black holes and associated radiation
• PeV photon and neutrino flares from galactic gamma-ray binaries
• Hadronic Gamma-Ray and Neutrino Emission from Cygnus X-3
• The X/gamma-ray correlation in NGC 4945 and the nature of its gamma-ray source
• Search for High-Energy Neutrino Emission from Galactic X-ray Binaries with IceCube
• High-energy gamma-ray activity from V404 Cygni detected by AGILE during the 2015 June outburst
• The 2010 May Flaring Episode of Cygnus X-3 in Radio, X-Rays, and γ-Rays
• Inverse Compton Emission from Relativistic Jets in Binary Systems
• High energy gamma-ray emission from compact galactic sources in the context of observations with the next generation Cherenkov Telescope Arrays
• Origin of Multi-band Emission from the Microquasar Cygnus X--1
• Simulations of neutrino and gamma-ray production from relativistic black-hole microquasar jets
• Dynamical and radiative simulations of $\gamma$-ray jets in microquasars
• INTEGRAL discovery of a high-energy tail in the microquasar Cygnus X-3
• Gamma-rays from anisotropic IC e^{\pm} pair cascades in microquasars: Application to Cyg X-3
• Cygnus X-3 as semi-hidden PeVatron
• Broadband Emission Spectra from the Cygnus X-3 Jet in the Soft Spectral State
• Non-Thermal Emission from Galactic Jets