Relativistic plasma jets are observed in many systems that host accreting black holes. According to theory, coiled magnetic fields close to the black hole accelerate and collimate the plasma, leading to a jet being launched1,2,3. Isolating emission from this acceleration and collimation zone is key to measuring its size and understanding jet formation physics. But this is challenging because emission from the jet base cannot easily be disentangled from other accreting components. Here, we show that rapid optical flux variations from an accreting Galactic black-hole binary are delayed with respect to X-rays radiated from close to the black hole by about 0.1 seconds, and that this delayed signal appears together with a brightening radio jet. The origin of these subsecond optical variations has hitherto been controversial4,5,6,7,8. Not only does our work strongly support a jet origin for the optical variations but it also sets a characteristic elevation of ≲103 Schwarzschild radii for the main inner optical emission zone above the black hole9, constraining both internal shock10 and magnetohydrodynamic11 models. Similarities with blazars12,13 suggest that jet structure and launching physics could potentially be unified under mass-invariant models. Two of the best-studied jetted black-hole binaries show very similar optical lags8,14,15, so this size scale may be a defining feature of such systems.
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Blandford, R. D. & Znajek, R. L. Electromagnetic extraction of energy from Kerr black holes. Mon. Not. R. Astron. Soc. 179, 433–456 (1977).
Blandford, R. D. & Payne, D. G. Hydrodynamic flows from accretion discs and the production of radio jets. Mon. Not. R. Astron. Soc. 199, 883–903 (1982).
Meier, D. L., Koide, S. & Uchida, Y. Magnetohydrodynamic production of relativistic jets. Science 291, 84–92 (2001).
Merloni, A. et al. Magnetic flares and the optical variability of the X-ray transient XTE J1118+480. Mon. Not. R. Astron. Soc. 318, L15–L19 (2000).
Malzac, J. et al. Jet–disc coupling through a common energy reservoir in the black hole XTE J1118+480. Mon. Not. R. Astron. Soc. 351, 253–264 (2004).
Yuan, F. et al. An accretion-jet model for black hole binaries: interpreting the spectral and timing features of XTE J1118+480. Astrophys. J. 620, 905–914 (2005).
Veledina, A. et al. Hot accretion flow in black hole binaries: a link connecting X-rays to the infrared. Mon. Not. R. Astron. Soc. 430, 3196–3212 (2013).
Gandhi, P. et al. Rapid optical and X-ray timing observations of GX 339–4: flux correlations at the onset of a low/hard state. Mon. Not. R. Astron. Soc. 390, L29–L33 (2008).
Markoff, S. et al. A jet model for the broadband spectrum of XTE J1118+480. Synchrotron emission from radio to X-rays in the Low/Hard spectral state. Astron. Astrophys. 372, L25–L28 (2001).
Malzac, J. The spectral energy distribution of compact jets powered by internal shocks. Mon. Not. R. Astron. Soc. 443, 299–317 (2014).
Polko, P. et al. Linking accretion flow and particle acceleration in jets: II. Self-similar jet models with full relativistic MHD gravitational mass. Mon. Not. R. Astron. Soc. 438, 959–970 (2014).
Marscher, A. et al. The inner jet of an active galactic nucleus as revealed by a radio-to-gamma-ray outburst. Nature 452, 966–969 (2008).
Cohen, M. H. et al. Studies of the jet in Bl Lacertae. I. Recollimation shock and moving emission features. Astrophys. J. 787, 151–160 (2014).
Casella, P. et al. Fast infrared variability from a relativistic jet in GX 339–4. Mon. Not. R. Astron. Soc. 404, L21–L25 (2010).
Gandhi, P. et al. Furiously fast and red: sub-second optical flaring in V404 Cyg during the 2015 outburst peak. Mon. Not. R. Astron. Soc. 459, 554–572 (2016).
Walton, D. J. et al. Living on a flare: relativistic reflection in V404 Cyg observed by NuSTAR during its summer 2015 outburst. Astrophys. J. 839, 110–132 (2017).
Loh, A. et al. High-energy gamma-ray observations of the accreting black hole V404 Cygni during its 2015 June outburst. Mon. Not. R. Astron. Soc. 462, L111–L115 (2016).
Gandhi, P. et al. Correlated optical and X-ray variability in V404 Cyg. Astron. Telegr. 7727 (2015).
Rodriguez, J. et al. Correlated optical, X-ray, and γ-ray flaring activity seen with INTEGRAL during the 2015 outburst of V404 Cygni. Astron. Astrophys. 581, L9–L13 (2015).
Durant, M. et al. High time resolution optical/X-ray cross-correlations for X-ray binaries: anticorrelation and rapid variability. Mon. Not. R. Astron. Soc. 410, 2329–2338 (2011).
Khargharia, J., Froning, C. S. & Robinson, E. L. Near-infrared spectroscopy of low-mass X-ray binaries: accretion disk contamination and compact object mass determination in V404 Cyg and Cen X-4. Astrophys. J. 716, 1105–1117 (2010).
Shahbaz, T. et al. Evidence for magnetic field compression in shocks within the jet of V404 Cyg. Mon. Not. R. Astron. Soc. 463, 1822–1830 (2016).
Motta, S. et al. The black hole binary V404 Cygni: an obscured AGN analogue. Mon. Not. R. Astron. Soc. 468, 981–993 (2017).
Jamil, O., Fender, R. P. & Kaiser, C. R. iShocks: X-ray binary jets with an internal shock model. Mon. Not. R. Astron. Soc. 401, 394–404 (2010).
Falcke, H., Körding, E. & Markoff, S. A scheme to unify low power accreting black holes. Astron. Astrophys. 414, 895–903 (2004).
Merloni, A. et al. A fundamental plane of black hole activity. Mon. Not. R. Astron. Soc. 345, 1057–1076 (2003).
Kanbach, G. et al. Correlated fast X-ray and optical variability in the black-hole candidate XTE J1118+480. Nature 414, 180–182 (2001).
Kimura, M. et al. Repetitive patterns in rapid optical variations in the nearby black-hole binary V404 Cygni. Nature 529, 54–58 (2016).
Dhillon, V. S. et al. ULTRACAM: an ultrafast, triple-beam CCD camera for high-speed astrophysics. Mon. Not. R. Astron. Soc. 378, 825–840 (2007).
Harrison, F. et al. The Nuclear Spectroscopic Telescope Array (NuSTAR) high-energy X-ray mission. Astrophys. J. 770, 103–131 (2013).
Bachetti, M. et al. No time for dead time: timing analysis of bright black hole binaries with NuSTAR. Astrophys. J. 800, 109–120 (2015).
Blackburn, J. K. FTOOLS: A FITS data processing and analysis software package. Astr. Soc. P. 77, 367–370 (1995).
Zwart, J. T. L. et al. The Arcminute Microkelvin Imager. Mon. Not. R. Astron. Soc. 391, 1545–1558 (2008).
Winkler, C. et al. The INTEGRAL mission. Astron. Astrophys. 411, L1–L6 (2003).
Kuulkers, E. INTEGRAL observations of V404 Cyg (GS 2023+338): public data products. Astron. Telegr. 7758 (2015).
Ubertini, P. et al. IBIS: the imager on-board INTEGRAL. Astron. Astrophys. 411, L131–L139 (2003).
Edelson, R. A. & Krolik, J. H. The discrete correlation function: a new method for analyzing unevenly sampled variability data. Astrophys. J. 333, 646–659 (1988).
Welsh, W. F. On the reliability of cross-correlation function lag determinations in active galactic nuclei. Publ. Astron. Soc. Pac. 111, 1347–1366 (1999).
Koratkar, A. P. & Gaskell, C. M. Structure and kinematics of the broad-line regions in active galaxies from IUE variability data. Astrophys. J. Suppl. 75, 719–750 (1991).
Peterson, B. M. et al. On uncertainties in cross-correlation lags and the reality of wavelength-dependent continuum lags in active galactic nuclei. Publ. Astron. Soc. Pacific. 110, 660–670 (1998).
This research has made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA), as well as the High Energy Astrophysics Science Archive Research Center. P.G. thanks the Science and Technology Facilities Council (STFC) for support (grant reference ST/J003697/2). ULTRACAM and V.S.D. are supported by STFC grant ST/M001350/1. P.G. thanks C.B. Markwardt, C.M. Boon, A.B. Hill, M. Fiocchi, K. Forster, A. Zoghbi and T. Muñoz-Darias for help and discussions. J.C. acknowledges financial support from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) under the 2015 Severo Ochoa Program MINECO SEV-2015-0548, and to the Leverhulme Trust through grant VP2-2015-04. T.R.M. acknowledges STFC (ST/L000733/1). J.M. acknowledges financial support from the French National Research Agency (CHAOS project ANR-12-BS05-0009), and D.A. thanks the Royal Society. S.M. acknowledges support from Netherlands Organisation for Scientific Research (NWO) VICI grant no. 639.043.513. We thank P. Wallace for use of his SLA C library. P.A.C. is grateful to the Leverhulme Trust for the award of a Leverhulme Emeritus Fellowship. Part of this research was supported by the UK-India UKIERI/UGC Thematic Partnership grants UGC 2014-15/02 and IND/CONT/E/14-15/355. This work profited from discussions carried out during a meeting organized at the International Space Science Institute (ISSI) Beijing by T. Belloni andD. Bhattacharya.
The authors declare no competing financial interests.
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Gandhi, P., Bachetti, M., Dhillon, V.S. et al. An elevation of 0.1 light-seconds for the optical jet base in an accreting Galactic black hole system. Nat Astron 1, 859–864 (2017). https://doi.org/10.1038/s41550-017-0273-3
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