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Living on a flare: Relativistic reflection in V404 Cyg observed by NuSTAR during Its summer 2015 outburst

Living on a flare: Relativistic reflection in V404 Cyg observed by NuSTAR during Its summer 2015 outburst
Living on a flare: Relativistic reflection in V404 Cyg observed by NuSTAR during Its summer 2015 outburst
We present first results from a series of NuSTAR observations of the black hole X-ray binary V404 Cyg obtained during its summer 2015 outburst, primarily focusing on observations during the height of this outburst activity. The NuSTAR data show extreme variability in both the flux and spectral properties of the source. This is partly driven by strong and variable line-of-sight absorption, similar to previous outbursts. The latter stages of this observation are dominated by strong flares, reaching luminosities close to Eddington. During these flares, the central source appears to be relatively unobscured and the data show clear evidence for a strong contribution from relativistic reflection, providing a means to probe the geometry of the innermost accretion flow. Based on the flare properties, analogies with other Galactic black hole binaries, and also the simultaneous onset of radio activity, we argue that this intense X-ray flaring is related to transient jet activity during which the ejected plasma is the primary source of illumination for the accretion disk. If this is the case, then our reflection modeling implies that these jets are launched in close proximity to the black hole (as close as a few gravitational radii), consistent with expectations for jet launching models that tap either the spin of the central black hole, or the very innermost accretion disk. Our analysis also allows us to place the first constraints on the black hole spin for this source, which we find to be {a}* > 0.92 (99% statistical uncertainty, based on an idealized lamp-post geometry).
black hole physics, X-rays: binaries, X-rays: individual: V404 Cyg
0004-637X
Walton, D.J.
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Mooley, K.
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King, A.L.
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Tomsick, J.A.
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Miller, J.M.
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Dauser, T.
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García, J.A.
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Bachetti, M.
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Brightman, M.
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Fabian, A.C.
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Forster, K.
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Fürst, F.
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Gandhi, P.
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Grefenstette, B.W.
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Harrison, F.A.
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Madsen, K.K.
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Meier, D.L.
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Middleton, M.J.
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Natalucci, L.
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Rahoui, F.
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Rana, V.
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Stern, D.
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Walton, D.J.
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Mooley, K.
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King, A.L.
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Tomsick, J.A.
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Miller, J.M.
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Dauser, T.
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García, J.A.
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Bachetti, M.
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Brightman, M.
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Fabian, A.C.
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Forster, K.
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Fürst, F.
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Gandhi, P.
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Grefenstette, B.W.
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Harrison, F.A.
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Madsen, K.K.
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Meier, D.L.
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Middleton, M.J.
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Natalucci, L.
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Rahoui, F.
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Rana, V.
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Stern, D.
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Walton, D.J., Mooley, K., King, A.L., Tomsick, J.A., Miller, J.M., Dauser, T., García, J.A., Bachetti, M., Brightman, M., Fabian, A.C., Forster, K., Fürst, F., Gandhi, P., Grefenstette, B.W., Harrison, F.A., Madsen, K.K., Meier, D.L., Middleton, M.J., Natalucci, L., Rahoui, F., Rana, V. and Stern, D. (2017) Living on a flare: Relativistic reflection in V404 Cyg observed by NuSTAR during Its summer 2015 outburst. The Astrophysical Journal, 839 (2), [110]. (doi:10.3847/1538-4357/aa67e8).

Record type: Article

Abstract

We present first results from a series of NuSTAR observations of the black hole X-ray binary V404 Cyg obtained during its summer 2015 outburst, primarily focusing on observations during the height of this outburst activity. The NuSTAR data show extreme variability in both the flux and spectral properties of the source. This is partly driven by strong and variable line-of-sight absorption, similar to previous outbursts. The latter stages of this observation are dominated by strong flares, reaching luminosities close to Eddington. During these flares, the central source appears to be relatively unobscured and the data show clear evidence for a strong contribution from relativistic reflection, providing a means to probe the geometry of the innermost accretion flow. Based on the flare properties, analogies with other Galactic black hole binaries, and also the simultaneous onset of radio activity, we argue that this intense X-ray flaring is related to transient jet activity during which the ejected plasma is the primary source of illumination for the accretion disk. If this is the case, then our reflection modeling implies that these jets are launched in close proximity to the black hole (as close as a few gravitational radii), consistent with expectations for jet launching models that tap either the spin of the central black hole, or the very innermost accretion disk. Our analysis also allows us to place the first constraints on the black hole spin for this source, which we find to be {a}* > 0.92 (99% statistical uncertainty, based on an idealized lamp-post geometry).

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Accepted/In Press date: 17 March 2017
e-pub ahead of print date: 21 April 2017
Keywords: black hole physics, X-rays: binaries, X-rays: individual: V404 Cyg

Identifiers

Local EPrints ID: 413010
URI: http://eprints.soton.ac.uk/id/eprint/413010
ISSN: 0004-637X
PURE UUID: 3222b67d-2c98-4914-adc7-639ac6b46c8d
ORCID for P. Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 10 Aug 2017 16:31
Last modified: 09 Oct 2020 16:36

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Contributors

Author: D.J. Walton
Author: K. Mooley
Author: A.L. King
Author: J.A. Tomsick
Author: J.M. Miller
Author: T. Dauser
Author: J.A. García
Author: M. Bachetti
Author: M. Brightman
Author: A.C. Fabian
Author: K. Forster
Author: F. Fürst
Author: P. Gandhi ORCID iD
Author: B.W. Grefenstette
Author: F.A. Harrison
Author: K.K. Madsen
Author: D.L. Meier
Author: M.J. Middleton
Author: L. Natalucci
Author: F. Rahoui
Author: V. Rana
Author: D. Stern

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