TY - JOUR
T1 - THE 2015 DECAY of the BLACK HOLE X-RAY BINARY V404 CYGNI
T2 - ROBUST DISK-JET COUPLING and A SHARP TRANSITION into QUIESCENCE
AU - Plotkin, R. M.
AU - Miller-Jones, J. C.A.
AU - Gallo, E.
AU - Jonker, P. G.
AU - Homan, J.
AU - Tomsick, J. A.
AU - Kaaret, P.
AU - Russell, D. M.
AU - Heinz, S.
AU - Hodges-Kluck, E. J.
AU - Markoff, S.
AU - Sivakoff, G. R.
AU - Altamirano, D.
AU - Neilsen, J.
N1 - Publisher Copyright:
© 2017. The American Astronomical Society. All rights reserved..
PY - 2017/1/10
Y1 - 2017/1/10
N2 - 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 ). During our 2015 campaign, the X-ray spectrum evolved rapidly from a hard photon index of Γ ≈ 1.6 (at LX ≈ 10 erg s-34 1) to a softer G ≈ 2 (at L ≈ 3 × 10 erg s- X 33 1). We argue that V404 Cygni reaching 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 . 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 ± 4minute, suggestive of X-ray variations propagating down a jet with a length of <3.0 au.
AB - 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 ). During our 2015 campaign, the X-ray spectrum evolved rapidly from a hard photon index of Γ ≈ 1.6 (at LX ≈ 10 erg s-34 1) to a softer G ≈ 2 (at L ≈ 3 × 10 erg s- X 33 1). We argue that V404 Cygni reaching 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 . 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 ± 4minute, suggestive of X-ray variations propagating down a jet with a length of <3.0 au.
KW - X-rays: binaries
KW - accretion, accretion disks
KW - stars: black holes
KW - stars: individual (V404 Cygni)
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U2 - 10.3847/1538-4357/834/2/104
DO - 10.3847/1538-4357/834/2/104
M3 - Article
AN - SCOPUS:85010029579
VL - 834
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
M1 - 104
ER -