THE 2015 DECAY of the BLACK HOLE X-RAY BINARY V404 CYGNI: ROBUST DISK-JET COUPLING and A SHARP TRANSITION into QUIESCENCE

R. M. Plotkin, J. C.A. Miller-Jones, E. Gallo, P. G. Jonker, J. Homan, J. A. Tomsick, P. Kaaret, D. M. Russell, S. Heinz, E. J. Hodges-Kluck, S. Markoff, G. R. Sivakoff, D. Altamirano, J. Neilsen

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Abstract

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.

Original languageEnglish (US)
Article number104
JournalAstrophysical Journal
Volume834
Issue number2
DOIs
StatePublished - Jan 10 2017

Keywords

  • X-rays: binaries
  • accretion, accretion disks
  • stars: black holes
  • stars: individual (V404 Cygni)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Plotkin, R. M., Miller-Jones, J. C. A., Gallo, E., Jonker, P. G., Homan, J., Tomsick, J. A., Kaaret, P., Russell, D. M., Heinz, S., Hodges-Kluck, E. J., Markoff, S., Sivakoff, G. R., Altamirano, D., & 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), [104]. https://doi.org/10.3847/1538-4357/834/2/104