The 2015 decay of the black hole X-ray binary V404 Cygni: robust disk-jet coupling and a sharp transition into quiescence

Journal Article · Tue Jan 10 04:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/834/2/104· OSTI ID:22869547

Plotkin, R. M.; Miller-Jones, J. C. A. ^[1]; Gallo, E.; Hodges-Kluck, E. J. ^[2]; Jonker, P. G. ^[3]; Homan, J.; Neilsen, J. ^[4]; Tomsick, J. A. ^[5]; Kaaret, P. ^[6]; Russell, D. M. ^[7]; Heinz, S. ^[8]; Markoff, S. ^[9]; Sivakoff, G. R. ^[10]

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1. International Centre for Radio Astronomy Research—Curtin University, GPO Box U1987, Perth, WA 6845 (Australia)
2. Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109 (United States)
3. SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, NL-3584 CA Utrecht (Netherlands)
4. MIT Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue 37-582D, Cambridge, MA 02139 (United States)
5. Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States)
6. Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States)
7. New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi (United Arab Emirates)
8. Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States)
9. Anton Pannekoek Institute for Astronomy, University of Amsterdam, 1098 XH Amsterdam (Netherlands)
10. Department of Physics, University of Alberta, 4-181 CCIS, Edmonton, AB T6G 2E1 (Canada)

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 2×10{sup 33}≲L{sub X}≲10{sup 34} erg s{sup −1}). During our 2015 campaign, the X-ray spectrum evolved rapidly from a hard photon index of Γ≈1.6 (at L{sub X}≈10{sup 34} erg s{sup −1}) to a softer Γ≈2 (at L{sub X}≈3×10{sup 33} erg s{sup −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 ≈8×10{sup 32} erg s{sup −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.

• OSTI ID: 22869547
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 834; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BINARY STARS
BLACK HOLES
CORRELATIONS
EMISSION
LUMINOSITY
SYNCHROTRON RADIATION
X-RAY SPECTRA