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Furiously fast and red: sub-second optical flaring in V404 Cyg during the 2015 outburst peak

Furiously fast and red: sub-second optical flaring in V404 Cyg during the 2015 outburst peak
Furiously fast and red: sub-second optical flaring in V404 Cyg during the 2015 outburst peak
We present observations of rapid (sub-second) optical flux variability in V404 Cyg during its 2015 June outburst. Simultaneous three-band observations with the ULTRACAM fast imager on four nights show steep power spectra dominated by slow variations on ?100–1000 s time-scales. Near the peak of the outburst on June 26, a dramatic change occurs and additional, persistent sub-second optical flaring appears close in time to giant radio and X-ray flaring. The flares reach peak optical luminosities of ? few × 1036 erg s?1. Some are unresolved down to a time resolution of 24 ms. Whereas the fast flares are stronger in the red, the slow variations are bluer when brighter. The redder slopes, emitted power and characteristic time-scales of the fast flares can be explained as optically thin synchrotron emission from a compact jet arising on size scales ?140–500 Gravitational radii (with a possible additional contribution by a thermal particle distribution). The origin of the slower variations is unclear. The optical continuum spectral slopes are strongly affected by dereddening uncertainties and contamination by strong H? emission, but the variations of these slopes follow relatively stable loci as a function of flux. Cross-correlating the slow variations between the different bands shows asymmetries on all nights consistent with a small red skew (i.e. red lag). X-ray reprocessing and non-thermal emission could both contribute to these. These data reveal a complex mix of components over five decades in time-scale during the outburst.
0035-8711
554-572
Gandhi, P.
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Littlefair, S.P.
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Hardy, L.K.
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Dhillon, V.S.
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Marsh, T.R.
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Shaw, A.W.
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Altamirano, D.
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Canallero-Garcia, M.D.
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Cesares, J.
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Casella, P.
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Castro=Tirado, A.J.
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Charles, P.A.
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Dallilar, Y.
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Eikenberry, S.
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Fender, R.P.
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Hynes, R.I.
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Knigge, C.
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Kuulkers, E.
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Mooley, K.
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Munoz-Darias, T.
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Pahari, M.
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Rahoui, F.
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Russell, D.M.
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Hernandez Santisteban, J.V.
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Shahbaz, T.
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Terndrup, D.M.
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Tomsick, J.
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Walton, D.J.
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Gandhi, P.
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Littlefair, S.P.
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Hardy, L.K.
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Dhillon, V.S.
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Marsh, T.R.
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Shaw, A.W.
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Altamirano, D.
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Canallero-Garcia, M.D.
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Cesares, J.
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Casella, P.
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Castro=Tirado, A.J.
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Charles, P.A.
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Dallilar, Y.
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Eikenberry, S.
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Fender, R.P.
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Hynes, R.I.
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Knigge, C.
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Kuulkers, E.
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Mooley, K.
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Munoz-Darias, T.
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Pahari, M.
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Rahoui, F.
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Russell, D.M.
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Hernandez Santisteban, J.V.
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Shahbaz, T.
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Terndrup, D.M.
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Tomsick, J.
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Walton, D.J.
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Gandhi, P., Littlefair, S.P., Hardy, L.K., Dhillon, V.S., Marsh, T.R., Shaw, A.W., Altamirano, D., Canallero-Garcia, M.D., Cesares, J., Casella, P., Castro=Tirado, A.J., Charles, P.A., Dallilar, Y., Eikenberry, S., Fender, R.P., Hynes, R.I., Knigge, C., Kuulkers, E., Mooley, K., Munoz-Darias, T., Pahari, M., Rahoui, F., Russell, D.M., Hernandez Santisteban, J.V., Shahbaz, T., Terndrup, D.M., Tomsick, J. and Walton, D.J. (2016) Furiously fast and red: sub-second optical flaring in V404 Cyg during the 2015 outburst peak. Monthly Notices of the Royal Astronomical Society, 459 (1), 554-572. (doi:10.1093/mnras/stw571).

Record type: Article

Abstract

We present observations of rapid (sub-second) optical flux variability in V404 Cyg during its 2015 June outburst. Simultaneous three-band observations with the ULTRACAM fast imager on four nights show steep power spectra dominated by slow variations on ?100–1000 s time-scales. Near the peak of the outburst on June 26, a dramatic change occurs and additional, persistent sub-second optical flaring appears close in time to giant radio and X-ray flaring. The flares reach peak optical luminosities of ? few × 1036 erg s?1. Some are unresolved down to a time resolution of 24 ms. Whereas the fast flares are stronger in the red, the slow variations are bluer when brighter. The redder slopes, emitted power and characteristic time-scales of the fast flares can be explained as optically thin synchrotron emission from a compact jet arising on size scales ?140–500 Gravitational radii (with a possible additional contribution by a thermal particle distribution). The origin of the slower variations is unclear. The optical continuum spectral slopes are strongly affected by dereddening uncertainties and contamination by strong H? emission, but the variations of these slopes follow relatively stable loci as a function of flux. Cross-correlating the slow variations between the different bands shows asymmetries on all nights consistent with a small red skew (i.e. red lag). X-ray reprocessing and non-thermal emission could both contribute to these. These data reveal a complex mix of components over five decades in time-scale during the outburst.

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Accepted/In Press date: 4 March 2016
e-pub ahead of print date: 14 March 2016
Published date: 11 June 2016
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 393656
URI: http://eprints.soton.ac.uk/id/eprint/393656
ISSN: 0035-8711
PURE UUID: a048502c-a767-4d1b-a173-3570cab108ff
ORCID for P. Gandhi: ORCID iD orcid.org/0000-0003-3105-2615
ORCID for D. Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 23 May 2016 14:30
Last modified: 17 Dec 2019 01:35

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Contributors

Author: P. Gandhi ORCID iD
Author: S.P. Littlefair
Author: L.K. Hardy
Author: V.S. Dhillon
Author: T.R. Marsh
Author: A.W. Shaw
Author: D. Altamirano ORCID iD
Author: M.D. Canallero-Garcia
Author: J. Cesares
Author: P. Casella
Author: A.J. Castro=Tirado
Author: P.A. Charles
Author: Y. Dallilar
Author: S. Eikenberry
Author: R.P. Fender
Author: R.I. Hynes
Author: C. Knigge
Author: E. Kuulkers
Author: K. Mooley
Author: T. Munoz-Darias
Author: M. Pahari
Author: F. Rahoui
Author: D.M. Russell
Author: J.V. Hernandez Santisteban
Author: T. Shahbaz
Author: D.M. Terndrup
Author: J. Tomsick
Author: D.J. Walton

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