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The response of relativistic outflowing gas to the inner accretion disk of a black hole


The brightness of an active galactic nucleus is set by the gas falling onto it from the galaxy, and the gas infall rate is regulated by the brightness of the active galactic nucleus; this feedback loop is the process by which supermassive black holes in the centres of galaxies may moderate the growth of their hosts1. Gas outflows (in the form of disk winds) release huge quantities of energy into the interstellar medium2, potentially clearing the surrounding gas. The most extreme (in terms of speed and energy) of these—the ultrafast outflows—are the subset of X-ray-detected outflows with velocities higher than 10,000 kilometres per second, believed to originate in relativistic (that is, near the speed of light) disk winds a few hundred gravitational radii from the black hole3. The absorption features produced by these outflows are variable4, but no clear link has been found between the behaviour of the X-ray continuum and the velocity or optical depth of the outflows, owing to the long timescales of quasar variability. Here we report the observation of multiple absorption lines from an extreme ultrafast gas flow in the X-ray spectrum of the active galactic nucleus IRAS 13224−3809, at 0.236 ± 0.006 times the speed of light (71,000 kilometres per second), where the absorption is strongly anti-correlated with the emission of X-rays from the inner regions of the accretion disk. If the gas flow is identified as a genuine outflow then it is in the fastest five per cent of such winds, and its variability is hundreds of times faster than in other variable winds, allowing us to observe in hours what would take months in a quasar. We find X-ray spectral signatures of the wind simultaneously in both low- and high-energy detectors, suggesting a single ionized outflow, linking the low- and high-energy absorption lines. That this disk wind is responding to the emission from the inner accretion disk demonstrates a connection between accretion processes occurring on very different scales: the X-ray emission from within a few gravitational radii of the black hole ionizing the disk wind hundreds of gravitational radii further away as the X-ray flux rises.

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Figure 1: High-energy absorption line detections.
Figure 2: RGS detection of flux-dependent absorption.
Figure 3: Flux dependence of the outflow.


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M.L.P., C.P., A.C.F. and A.L. acknowledge support from the European Research Council through Advanced Grant on Feedback 340492. W.N.A. and G.M. acknowledge support from the European Union Seventh Framework Programme (FP7/2013-2017) under grant agreement number 312789, StrongGravity. D.J.K.B. acknowledges support from the Science and Technology Facilities Council. This work is based on observations with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. D.R.W. is supported by NASA through Einstein Postdoctoral Fellowship grant number PF6-170160, awarded by the Chandra X-ray Center, operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. This work 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 NASA. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center and the California Institute of Technology.

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Authors and Affiliations



M.L.P. wrote the manuscript with comments from all authors and performed the flux-resolved EPIC-pn analysis and line detections. C.P. analysed the RGS data and did the physical modelling. A.C.F. led the XMM-Newton proposal. All authors were involved with the proposal at various stages.

Corresponding author

Correspondence to Michael L. Parker.

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The authors declare no competing financial interests.

Additional information

Reviewer Information Nature thanks G. Risaliti and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Figure 1 The 0.3–10-keV lightcurve of the new observations of IRAS 13224−3809.

We use 1-ks bins, with gaps between observations removed. The vertical dashed lines show where observations start and finish, and the horizontal dashed lines show the threshold flux levels. Low-, medium- and high-flux intervals are distributed throughout the lightcurve, and are coloured green, yellow and red, respectively.

Extended Data Figure 2 The 8–8.5-keV EPIC-pn image showing the high instrumental background outside the central chips.

Source and background extraction regions marked by small and large white circles, respectively, for a representative observation (0780561301).

Extended Data Figure 3 The low-flux spectrum without background subtraction.

The spectrum is fitted with a power law. The ultrafast-outflow line is clearly still visible in the residuals, and only slightly reduced in strength. All errors are ±1σ, and energies are in the observer’s frame. ‘Ratio’ indicates the ratio of data to model output.

Extended Data Figure 4 EPIC-pn spectroscopy.

a, Data and residuals of the EPIC-pn data fitted with reflection, with and without an outflowing absorption component. b, Residuals of the EPIC-pn data fitted with a power law from 4–5 keV and 9–10 keV, showing the broad iron line and ultrafast-outflow (UFO) line. Error bars are 1σ, and energies are in the source rest frame.

Extended Data Figure 5 RGS first-order and second-order (small panel) stacked spectra of all 17 observations.

Transitions of typical interstellar absorption lines are labelled. Additional features of non-interstellar-medium origin are indicated with a dashed red line and two question marks. Above 33 Å the RGS spectrum is affected by high background. Error bars are 1σ, and energies are in the source rest frame.

Extended Data Table 1 Phenomenological model fit
Extended Data Table 2 Physical model fit

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Parker, M., Pinto, C., Fabian, A. et al. The response of relativistic outflowing gas to the inner accretion disk of a black hole. Nature 543, 83–86 (2017).

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