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An elevation of 0.1 light-seconds for the optical jet base in an accreting Galactic black hole system

Gandhi, P. and Harrison, F. A. (2017) An elevation of 0.1 light-seconds for the optical jet base in an accreting Galactic black hole system. Nature Astronomy, 1 (12). pp. 859-864. ISSN 2397-3366.

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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 launched. 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. Not only does our work strongly support a jet origin for the optical variations but it also sets a characteristic elevation of ≲10^3 Schwarzschild radii for the main inner optical emission zone above the black hole, constraining both internal shock and magnetohydrodynamic models. Similarities with blazars 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 lags, so this size scale may be a defining feature of such systems.

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Gandhi, P.0000-0003-3105-2615
Harrison, F. A.0000-0003-2992-8024
Alternate Title:The optical jet base in a Galactic black hole transient elevated by 0.1 light-seconds
Additional Information:© 2017 Macmillan Publishers Limited, part of Springer Nature. Received: 24 February 2017; Accepted: 07 September 2017; Published online: 30 October 2017. 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 and D. Bhattacharya. Contributions: P.G. wrote the ULTRACAM proposal, analysed the data and wrote the paper. The ULTRACAM observations were coordinated and carried out by L.K.H., S.P.L., V.S.D. and T.R.M. The X-ray observations were proposed by D.J.W., coordinated by D.S., J.A.T. and F.A.H., and the timing data analysed by M.B. Radio data were obtained and analysed by R.P.F. and K.M. INTEGRAL data were arranged by E.K. The remaining authors provided insight into jet physics constraints (S.M., J.M., C.C.), cross-correlation analyses (P.C., R.I.H., C.K., C.F., M.P., F.V.) and placing the source in context (D.A., J.C., P.A.C., D.M.R., F.R., A.W.S.). All authors read and commented on multiple versions of the manuscript. Competing interests: The authors declare no competing financial interests.
Group:Space Radiation Laboratory, NuSTAR, Astronomy Department
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)ST/J003697/2
Science and Technology Facilities Council (STFC)ST/M001350/1
Ministerio de Economía, Industria y Competitividad (MINECO)UNSPECIFIED
Centro de Excelencia Severo OchoaSEV-2015-0548
Leverhulme TrustVP2-2015-04
Science and Technology Facilities Council (STFC)ST/L000733/1
Agence Nationale pour la Recherche (ANR)ANR-12-BS05-0009
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)639.043.513
UK India Education Research Initiative (UKIERI)UGC 2014-15/02
UK India Education Research Initiative (UKIERI)IND/CONT/E/14-15/355
Issue or Number:12
Record Number:CaltechAUTHORS:20170829-115834040
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:80902
Deposited By: George Porter
Deposited On:30 Oct 2017 23:52
Last Modified:03 Oct 2019 18:36

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