Jet radio emission in Cygnus X-1 and its orbital modulation

Abstract

We present results of our detailed theoretical study of the observed orbital modulation of the radio emission in Cyg X-1. The modulation occurs due to free-free absorption in the wind from the companion star varying with the orbital phase, and our results put strong constraints on the spatial distribution of the jet radio emission at the frequencies of 2-15 GHz. A crucial role in enhancing the asymmetry of the wind absorption suffered by the jet emission is played by the irradiation by X-rays emitted in the vicinity of the black hole. This increases the wind temperature by more than order of magnitude with respect to that of the wind of an isolated supergiant. The observed phase lags of the minima of the radio emission with respect to the spectroscopic zero phase strongly imply the bulk of the mass of the jet is nonrelativistic (~5 x 10^8 cm/s) within the jet core. The jet can, however, become relativistic outside the core. Also, the jet can have a two-component structure, being slow on the outside and fast inside, in which case its synchrotron-emitting part may be relativistic already in the core. We also consider the observed superorbital modulation of the radio emission (with the period of ~150 d) and find it can be explained by a jet precession both causing variable wind absorption and changing the jet Doppler factor. Finally, we consider the case of Cyg X-3, and show that its lack of observable orbital radio modulation (in spite of strong modulation of X-rays) is explained by that system being both much more compact and much more luminous than Cyg X-1.

arXiv commentAccepted for publication in MNRAS; new revised version with small changes; 13 pages, 16 figures

References in corpus (23)

• A universal radio/X-ray correlation in low/hard state black hole binaries
• A relativistic jet from Cygnus X-1 in the low/hard X-ray state
• Jets in neutron star X-ray binaries: a comparison with black holes
• A dark jet dominates the power output of the stellar black hole Cygnus X-1
• The Nature of SS433 and the Ultraluminous X-ray Sources
• Understanding the long-term spectral variability of Cygnus X-1 with BATSE and ASM observations
• A unified accretion-ejection paradigm for Black Hole X-ray Binaries
• Orbital, precessional and flaring variability of Cygnus X-1
• The very flat radio - millimetre spectrum of Cygnus X-1
• Broad band spectrum of Cygnus X-1 in two spectral states with BeppoSAX
• Evolutionary constraints on the masses of the components of HDE 226868/Cyg X-1 binary system
• On the precession of accretion discs in X-ray binaries
• The flat synchrotron spectra of partially self-absorbed jets revisited
• Wind Accretion and State Transitions in Cygnus X-1
• A transient relativistic radio jet from Cygnus X-1
• Orbital modulation and longer-term variability in the radio emission from Cygnus X-1
• Composition, collimation, contamination: the jet of Cygnus X-1
• Long term variability of Cygnus X-1, III. Radio-X-ray correlations
• Revealing the Focused Companion Wind in Cygnus X-1 with Chandra
• Periodic long-term X-ray and radio variability of Cygnus X-1
• First INTEGRAL observations of Cygnus X-3
• The orbital modulation in the radio emission of Cygnus X-1
• Cygnus X-3 with ISO: investigating the wind

Cited by in corpus (26)

• Cygnus X-1 contains a 21-solar mass black hole -- implications for massive star winds
• Superorbital variability of X-ray and radio emission of Cyg X-1 - II. Dependence of the orbital modulation and spectral hardness on the superorbital phase
• Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system. I. The non-dip spectrum in the low/hard state
• High-energy gamma-ray emission from Cyg X-1 measured by Fermi and its theoretical implications
• The MeV spectral tail in Cyg X-1 and optically-thin emission of jets
• A compact pulsar wind nebula model of the gamma-ray loud binary LS I +61 303
• Effects of the stellar wind on X-ray spectra of Cygnus X-3
• The Ultraviolet Spectrum and Physical Properties of the Mass Donor Star in HD 226868 = Cygnus X-1
• Leptonic secondary emission in a hadronic microquasar model
• Energetics of a black hole: constraints on the jet velocity and the nature of the X-ray emitting region in Cyg X-1
• A new lepto-hadronic model applied to the first simultaneous multiwavelength data set for Cygnus X--1
• A weak compact jet in a soft state of Cygnus X-1
• A classification of the X-ray and radio states of Cyg X-3 and their long-term correlations
• X-ray variability patterns and radio/X-ray correlations in Cyg X-1
• The structure of the jet in Cyg X-1 inferred from orbital modulation of the radio emission
• The effects of the stellar wind and orbital motion on the jets of high-mass microquasars
• Global Simulations of the Interaction of Microquasar Jets with a Stellar Wind in High-Mass X-ray Binaries
• Superorbital variability of X-ray and radio emission of Cyg X-1. I. Emission anisotropy of precessing sources
• Search for very-high-energy gamma-ray emission from the microquasar Cygnus X-1 with the MAGIC telescopes
• Evidence for a black hole spin--orbit misalignment in the X-ray binary Cyg X-1
• Soft gamma-ray sources detected by INTEGRAL
• What are the Composition and Power of the Jet in Cyg X-1?
• Investigating the mini and giant radio flare episodes of Cygnus X-3
• Eclipses of jets and discs of X-ray binaries as a powerful tool for understanding jet physics and binary parameters
• Spectroscopic modelling of two high-mass X-ray binaries, Cyg X--3 and 4U 1538--522
• Unprecedentedly bright X-ray flaring in Cygnus X-1 observed by INTEGRAL