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Optical and X-ray correlations during the 2015 outburst of the black hole V404 Cyg

Optical and X-ray correlations during the 2015 outburst of the black hole V404 Cyg
Optical and X-ray correlations during the 2015 outburst of the black hole V404 Cyg
We present a serendipitous multiwavelength campaign of optical photometry simultaneous with Integral X-ray monitoring of the 2015 outburst of the black hole V404 Cyg. Large-amplitude optical variability is generally correlated with X-rays, with lags of order a minute or less compatible with binary light travel time-scales or jet ejections. Rapid optical flaring on time-scales of seconds or less is incompatible with binary light-travel time-scales and has instead been associated with synchrotron emission from a jet. Both this rapid jet response and the lagged and smeared one can be present simultaneously. The optical brightness is not uniquely determined by the X-ray brightness, but the X-ray/optical relationship is bounded by a lower envelope such that at any given optical brightness there is a maximum X-ray brightness seen. This lower envelope traces out a Fopt∝F0.54X relation that can be approximately extrapolated back to quiescence. Rapid optical variability is only seen near this envelope, and these periods correspond to the hardest hard X-ray colours. This correlation between hard X-ray colour and optical variability (and anticorrelation with optical brightness) is a novel finding of this campaign, and apparently a facet of the outburst behaviour in V404 Cyg. It is likely that these correlations are driven by changes in the central accretion rate and geometry.
0035-8711
60-78
Hynes, R.I.
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Robinson, E.L.
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Terndrup, D.M.
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Gandhi, P.
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Froning, C.S.
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Wagner, R. M.
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Starrfield, S.
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Dhillon, V.S.
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Marsh, T.R.
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Hynes, R.I.
1409ca82-99c4-4b68-9a67-d5c9d67c636b
Robinson, E.L.
7bbeb5d3-0ebe-49e1-875a-ea76fc5689ff
Terndrup, D.M.
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Gandhi, P.
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Froning, C.S.
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Wagner, R. M.
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Starrfield, S.
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Dhillon, V.S.
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Marsh, T.R.
85d03859-70b1-4f83-958e-e743e1e0c59a

Hynes, R.I., Robinson, E.L., Terndrup, D.M., Gandhi, P., Froning, C.S., Wagner, R. M., Starrfield, S., Dhillon, V.S. and Marsh, T.R. (2019) Optical and X-ray correlations during the 2015 outburst of the black hole V404 Cyg. Monthly Notices of the Royal Astronomical Society, 487 (1), 60-78. (doi:10.1093/mnras/stz1238).

Record type: Article

Abstract

We present a serendipitous multiwavelength campaign of optical photometry simultaneous with Integral X-ray monitoring of the 2015 outburst of the black hole V404 Cyg. Large-amplitude optical variability is generally correlated with X-rays, with lags of order a minute or less compatible with binary light travel time-scales or jet ejections. Rapid optical flaring on time-scales of seconds or less is incompatible with binary light-travel time-scales and has instead been associated with synchrotron emission from a jet. Both this rapid jet response and the lagged and smeared one can be present simultaneously. The optical brightness is not uniquely determined by the X-ray brightness, but the X-ray/optical relationship is bounded by a lower envelope such that at any given optical brightness there is a maximum X-ray brightness seen. This lower envelope traces out a Fopt∝F0.54X relation that can be approximately extrapolated back to quiescence. Rapid optical variability is only seen near this envelope, and these periods correspond to the hardest hard X-ray colours. This correlation between hard X-ray colour and optical variability (and anticorrelation with optical brightness) is a novel finding of this campaign, and apparently a facet of the outburst behaviour in V404 Cyg. It is likely that these correlations are driven by changes in the central accretion rate and geometry.

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Optical and X-ray correlations during the 2015 outburst of the black hole V404 Cyg - Accepted Manuscript
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Accepted/In Press date: 1 May 2019
e-pub ahead of print date: 8 May 2019
Additional Information: arXiv is AM

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Local EPrints ID: 433064
URI: http://eprints.soton.ac.uk/id/eprint/433064
ISSN: 0035-8711
PURE UUID: 79f3abd5-848f-4f64-b1c5-cc64290ec769
ORCID for P. Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 07 Aug 2019 16:30
Last modified: 07 Oct 2020 02:06

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Contributors

Author: R.I. Hynes
Author: E.L. Robinson
Author: D.M. Terndrup
Author: P. Gandhi ORCID iD
Author: C.S. Froning
Author: R. M. Wagner
Author: S. Starrfield
Author: V.S. Dhillon
Author: T.R. Marsh

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