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Characterizing x-ray and radio emission in the black hole x-ray binary V404 Cygni during quiescence

Characterizing x-ray and radio emission in the black hole x-ray binary V404 Cygni during quiescence
Characterizing x-ray and radio emission in the black hole x-ray binary V404 Cygni during quiescence
We present results from multi-wavelength simultaneous X-ray and radio observations of the black hole X-ray binary V404 Cyg in quiescence. Our coverage with NuSTAR provides the very first opportunity to study the X-ray spectrum of V404 Cyg at energies above 10 keV. The unabsorbed broadband (0.3–30 keV) quiescent luminosity of the source is 8.9 × 1032 erg s-1 for a distance of 2.4 kpc. The source shows clear variability on short timescales (an hour to a couple of hours) in the radio, soft X-ray, and hard X-ray bands in the form of multiple flares. The broadband X-ray spectra obtained from XMM-Newton and NuSTAR can be characterized with a power-law model having a photon index of Γ = 2.12 ± 0.07 (90% confidence errors); however, residuals at high energies indicate spectral curvature significant at a 3σ confidence level with the e-folding energy of the cutoff as ${20}_{-7}^{+20}$ keV. Such curvature can be explained using synchrotron emission from the base of a jet outflow. Radio observations using the VLA reveal that the spectral index evolves on very fast timescales (as short as 10 minutes), switching between optically thick and thin synchrotron emission, possibly due to instabilities in the compact jet or stochastic instabilities in the accretion rate. We explore different scenarios to explain this very fast variability.
1538-4357
1-10
Rana, Vikram
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Loh, Alan
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Corbel, Stephane
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Tomsick, John A.
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Chakrabarty, Deepto
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Walton, Dominic J.
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Barret, Didier
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Boggs, Steven E.
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Christensen, Finn E.
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Craig, William
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Fuerst, Felix
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Gandhi, Poshak
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Grefenstette, Brian W.
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Hailey, Charles
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Harrison, Fiona A.
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Madsen, Kristin K.
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Rahoui, Farid
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Stern, Daniel
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Tendulkar, Shriharsh
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Zhang, William W.
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Rana, Vikram
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Loh, Alan
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Corbel, Stephane
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Tomsick, John A.
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Chakrabarty, Deepto
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Walton, Dominic J.
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Barret, Didier
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Boggs, Steven E.
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Christensen, Finn E.
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Craig, William
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Fuerst, Felix
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Gandhi, Poshak
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Grefenstette, Brian W.
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Hailey, Charles
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Harrison, Fiona A.
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Madsen, Kristin K.
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Rahoui, Farid
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Stern, Daniel
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Tendulkar, Shriharsh
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Zhang, William W.
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Rana, Vikram, Loh, Alan, Corbel, Stephane, Tomsick, John A., Chakrabarty, Deepto, Walton, Dominic J., Barret, Didier, Boggs, Steven E., Christensen, Finn E., Craig, William, Fuerst, Felix, Gandhi, Poshak, Grefenstette, Brian W., Hailey, Charles, Harrison, Fiona A., Madsen, Kristin K., Rahoui, Farid, Stern, Daniel, Tendulkar, Shriharsh and Zhang, William W. (2016) Characterizing x-ray and radio emission in the black hole x-ray binary V404 Cygni during quiescence. The Astrophysical Journal, 821 (2), 1-10. (doi:10.3847/0004-637X/821/2/103).

Record type: Article

Abstract

We present results from multi-wavelength simultaneous X-ray and radio observations of the black hole X-ray binary V404 Cyg in quiescence. Our coverage with NuSTAR provides the very first opportunity to study the X-ray spectrum of V404 Cyg at energies above 10 keV. The unabsorbed broadband (0.3–30 keV) quiescent luminosity of the source is 8.9 × 1032 erg s-1 for a distance of 2.4 kpc. The source shows clear variability on short timescales (an hour to a couple of hours) in the radio, soft X-ray, and hard X-ray bands in the form of multiple flares. The broadband X-ray spectra obtained from XMM-Newton and NuSTAR can be characterized with a power-law model having a photon index of Γ = 2.12 ± 0.07 (90% confidence errors); however, residuals at high energies indicate spectral curvature significant at a 3σ confidence level with the e-folding energy of the cutoff as ${20}_{-7}^{+20}$ keV. Such curvature can be explained using synchrotron emission from the base of a jet outflow. Radio observations using the VLA reveal that the spectral index evolves on very fast timescales (as short as 10 minutes), switching between optically thick and thin synchrotron emission, possibly due to instabilities in the compact jet or stochastic instabilities in the accretion rate. We explore different scenarios to explain this very fast variability.

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Accepted/In Press date: 10 February 2016
e-pub ahead of print date: 19 April 2016
Published date: 19 April 2016
Organisations: Astronomy Group

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Local EPrints ID: 399906
URI: http://eprints.soton.ac.uk/id/eprint/399906
ISSN: 1538-4357
PURE UUID: 75f23971-ddd5-436c-8963-99bc0b9e6448
ORCID for Poshak Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 02 Sep 2016 11:09
Last modified: 17 Dec 2019 01:34

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Contributors

Author: Vikram Rana
Author: Alan Loh
Author: Stephane Corbel
Author: John A. Tomsick
Author: Deepto Chakrabarty
Author: Dominic J. Walton
Author: Didier Barret
Author: Steven E. Boggs
Author: Finn E. Christensen
Author: William Craig
Author: Felix Fuerst
Author: Poshak Gandhi ORCID iD
Author: Brian W. Grefenstette
Author: Charles Hailey
Author: Fiona A. Harrison
Author: Kristin K. Madsen
Author: Farid Rahoui
Author: Daniel Stern
Author: Shriharsh Tendulkar
Author: William W. Zhang

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