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The 2015 Decay of the Black Hole X-ray Binary V404 Cygni: Robust Disk-Jet Coupling and a Sharp Transition into Quiescence

Plotkin, R. M. and Miller-Jones, J. C. A. and Gallo, E. and Jonker, P. G. and Homan, J. and Tomsick, J. A. and Kaaret, P. and Russell, D. M. and Heinz, S. and Hodges-Kluck, E. J. and Markoff, S. and Sivakoff, G. R. and Altamirano, D. and Neilsen, J. (2017) The 2015 Decay of the Black Hole X-ray Binary V404 Cygni: Robust Disk-Jet Coupling and a Sharp Transition into Quiescence. Astrophysical Journal, 834 (2). Art. No. 104. ISSN 1538-4357.

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We present simultaneous X-ray and radio observations of the black hole X-ray binary V404 Cygni at the end of its 2015 outburst. From 2015 July 11–August 5, we monitored V404 Cygni with Chandra, Swift, and NuSTAR in the X-ray, and with the Karl G. Jansky Very Large Array and the Very Long Baseline Array in the radio, spanning a range of luminosities that were poorly covered during its previous outburst in 1989 (our 2015 campaign covers 2 x 10^(33) ≾ L_X ≾ 10^(34) erg s^(-1)). During our 2015 campaign, the X-ray spectrum evolved rapidly from a hard photon index of Γ ≈ 1.6 (at L_X ≈ 10^(34) erg s^(-1)) to a softer Γ ≈ 2 (at L_X ≈ 3 x 10^(33) erg s^(-1)). We argue that V404 Cygni reaching Γ ≈ 2 marks the beginning of the quiescent spectral state, which occurs at a factor of ≈3–4 higher X-ray luminosity than the average pre-outburst luminosity of ≈8 x 10^(32) erg s^(-1). V404 Cygni falls along the same radio/X-ray luminosity correlation that it followed during its previous outburst in 1989, implying a robust disk-jet coupling. We exclude the possibility that a synchrotron-cooled jet dominates the X-ray emission in quiescence, leaving synchrotron self-Compton from either a hot accretion flow or from a radiatively cooled jet as the most likely sources of X-ray radiation, and/or particle acceleration along the jet becoming less efficient in quiescence. Finally, we present the first indications of correlated radio and X-ray variability on minute timescales in quiescence, tentatively measuring the radio emission to lag the X-ray by 15 ± 4 minute, suggestive of X-ray variations propagating down a jet with a length of <3.0 au.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Plotkin, R. M.0000-0002-7092-0326
Miller-Jones, J. C. A.0000-0003-3124-2814
Jonker, P. G.0000-0001-5679-0695
Homan, J.0000-0001-8371-2713
Tomsick, J. A.0000-0001-5506-9855
Kaaret, P.0000-0002-3638-0637
Russell, D. M.0000-0002-3500-631X
Heinz, S.0000-0002-8433-8652
Hodges-Kluck, E. J.0000-0002-2397-206X
Markoff, S.0000-0001-9564-0876
Sivakoff, G. R.0000-0001-6682-916X
Altamirano, D.0000-0002-3422-0074
Neilsen, J.0000-0002-8247-786X
Additional Information:© 2017 The American Astronomical Society. Received 2016 September 14; revised 2016 October 25; accepted 2016 November 3; published 2017 January 5. We thank the anonymous referee for constructive comments that improved this manuscript. We are especially grateful to the Chandra, VLA, and Swift teams for coordinating these observations, particularly Belinda Wilkes and Neil Gehrels for approving the Chandra and Swift observations, and especially Scott Wolk for patiently assisting with multiple iterations of our Chandra observing setup. We also thank Mark Claussen, Gustaaf van Moorsel, and Heidi Medlin for their assistance with the VLA observations. We thank Arash Bahramian for helpful discussions on the X-ray decay timescale that assisted the timing of our trigger, and Thomas Russell for assistance with the radio data reduction. R.M.P. acknowledges support from Curtin University through the Peter Curran Memorial Fellowship. J.C.A.M.-J. is supported by an Australian Research Council Future Fellowship (FT140101082). G.R.S. acknowledges support from NSERC Discovery Grants. D.A. acknowledges support from the Royal Society. Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number GO5-16032A issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. The scientific results reported in this article are based to a significant degree on observations made by the Chandra X-ray Observatory. This research has made use of software provided by the Chandra X-ray Center (CXC) in the application packages CIAO. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Facilities: CXO - Chandra X-ray Observatory satellite, NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, Swift - Swift Gamma-Ray Burst Mission, VLA. - Very Large Array Software: CIAO (v4.8; Fruscione et al. 2006), HEASOFT, NUSTARDAS (v1.6.0), ISIS (Houck & Denicola 2000), CASA (v4.5; McMullin et al. 2007).
Subject Keywords:accretion, accretion disks – stars: black holes – stars: individual (V404 Cygni) – X-rays: binaries
Issue or Number:2
Record Number:CaltechAUTHORS:20161110-080756178
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Official Citation:R. M. Plotkin et al 2017 ApJ 834 104
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71909
Deposited By: Joy Painter
Deposited On:10 Nov 2016 22:49
Last Modified:09 Mar 2020 13:19

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