A quantitative explanation of the radio--X-ray correlation in black-hole X-ray binaries

Abstract

The observed correlation between the radio and X-ray fluxes in the hard state of black-hole X-ray binaries (BHXRBs) has been around for more than two decades. It is currently accepted that the hard X-rays in BHXRBs come from Comptonization in the corona and the radio emission from the relativistic jet (Lorentz $\gamma >>1$), which is a narrow structure of a few $R_g=GM/c^2$ at its base. The relativistic jet and the corona, however, are separate entities with hardly any communication between them, apart from the fact that both are fed from the accreting matter. It is also widely accepted that the accretion flow around black holes in BHXRBs consists of an outer thin disk and an inner hot flow. From this hot inner flow, an outflow emanates in the hard and hard-intermediate states of the source. By considering Compton up-scattering of soft disk photons in the outflow (i.e., in the outflowing corona, which is a wider structure, tens to hundreds of $R_g$ at its base, with low Lorentz gamma) as the mechanism that produces the hard X-ray spectrum, we have been able to explain quantitatively a number of observed correlations. Here, we demonstrate that this outflowing corona can also explain quantitatively the observed radio - X-ray correlation. In addition, we make the following theoretical predictions for GX 339-4: 1) the radio flux in the hard and hard-intermediate states should be a bell-shaped curve as a function of the photon-number spectral index Gamma, 2) the radio - X-ray correlation should break down when the source moves from the hard to the hard-intermediate state and instead the radio flux should first increase sharply in the hard-intermediate state and then decrease also sharply, in a very narrow range of the X-ray flux, and 3) the X-ray polarization will be parallel to the outflow in the hard state and perpendicular to it in the hard-intermediate one.

Accepted for publication in A&A

References in corpus (13)

• Modelling the behaviour of accretion flows in X-ray binaries
• Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1
• An extremely powerful long-lived superluminal ejection from the black hole MAXI J1820+070
• A jet model for Galactic black-hole X-ray sources: Some constraining correlations
• Polarized X-rays from windy accretion in Cygnus X-1
• A unified accretion-ejection paradigm for black hole X-ray binaries. IV. Replication of the 2010--2011 activity cycle of GX 339-4
• Rapid compact jet quenching in the Galactic black hole candidate X-ray binary MAXI J1535-571
• Accretion and ejection in black-hole X-ray transients
• The photon-index - time-lag correlation in black-hole X-ray binaries
• A quantitative explanation of the type-B QPOs in GX 339-4
• Observations of the Disk/Jet Coupling of MAXI J1820+070 During its Descent to Quiescence
• Illumination of the accretion disk in black hole binaries: An extended jet as the primary source of hard X-rays
• Inclination effects on the X-ray emission of Galactic black-hole binaries

Cited by in corpus (4)

• Bulk Motions in the Black Hole Jet Sheath as a Candidate for the Comptonizing Corona
• Joint ALMA/X-ray monitoring of the radio-quiet type 1 AGN IC 4329A
• Millimeter emission from supermassive black hole coronae
• The role of outflows in black-hole X-ray binaries