On the Radio/X-ray Correlation in Microquasars

Abstract

[Context] The broadband spectral energy distribution of microquasars has proven to be a valuable tool for assessing the roles of jets and accretion flows in microquasars, as well as the coupling between the two. The coupling might manifest itself observationally in the correlated radio and X-ray variabilities of a source. Such a radio/X-ray correlation has indeed been seen in several microquasars during the low-hard state and subsequently been claimed to be universal for all. If proven, the universal correlation would have profound implications on theoretical models. However, there is already observational evidence that suggests otherwise. [Aims] In this paper, we critically examine the radio/X-ray correlation in a sample of microquasars, in the low-hard state as well as during state transitions, with a goal of testing the claimed universality of the correlation on observational grounds. [Methods] We have assembled a comprehensive data set from the simultaneous/contemporaneous radio and X-ray observations of representative microquasars. The data have allowed us to quantify the radio/X-ray correlation on a source by source basis. [Results] We find that the radio/X-ray correlation of microquasars exhibits diverse behaviors, both in the low-hard and transitional states, ranging from being very week (or none at all) to very strong. There is even a hint of spectral dependence of the correlation in some cases. [Conclusions] Our results rule out the claimed universality of the radio/X-ray correlation of microquasars, even for the low-hard state. On the other hand, we do find that the radio and X-ray variabilities are, to varying degrees, correlated in most cases.

6 pages, 4 figures, accepted by A&A

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• Assessing luminosity correlations via cluster analysis: Evidence for dual tracks in the radio/X-ray domain of black hole X-ray binaries
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• The black hole candidate MAXIJ1659-152 in and towards quiescence in X-ray and radio
• The disc-jet coupling in the neutron star X-ray binary Aquila X-1
• X-ray and radio variability in the low luminosity Active Galactic Nucleus NGC 7213
• A new fundamental plane for radiatively efficient black-hole sources
• Investigating the disc-jet coupling in accreting compact objects using the black hole candidate Swift J1753.5-0127
• On the nature of the "radio quiet" black hole binaries
• Interpreting the radio/X-ray correlation of black hole sources based on the accretion-jet model
• Fundamental Plane of Black Hole Activity in Quiescent Regime
• The nature of the intranight variability of radio-quiet quasars
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• Revisit the fundamental plane of black-hole activity from sub-Eddington to quiescent state
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• A disc corona-jet model for the radio/X-ray correlation in black hole X-ray binaries
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• Up and Down the Black Hole Radio/X-ray Correlation: the 2017 mini-outbursts from Swift J1753.5-0127
• Observations of the Disk/Jet Coupling of MAXI J1820+070 During its Descent to Quiescence
• A population of compact radio variables and transients in the radio bright zone at the Galactic center observed with the Jansky Very Large Array
• Modeling the hard states of three black hole candidates
• Black Hole Fundamental Plane in Low-Excitation Radio Galaxies
• Modeling the Broadband Spectral Energy Distribution of the Microquasars XTE J1550-564 and H 1743-322
• Modeling the Spectrum of IGR J17177-3656