Abstract
Since the 1995 discovery of the broad iron K-line emission from the Seyfert galaxy MCG–6-30-15 (ref. 1), broad iron K lines have been found in emission from several other Seyfert galaxies2, from accreting stellar-mass black holes3 and even from accreting neutron stars4. The iron K line is prominent in the reflection spectrum5,6 created by the hard-X-ray continuum irradiating dense accreting matter. Relativistic distortion7 of the line makes it sensitive to the strong gravity and spin of the black hole8. The accompanying iron L-line emission should be detectable when the iron abundance is high. Here we report the presence of both iron K and iron L emission in the spectrum of the narrow-line Seyfert 1 galaxy9 1H 0707-495. The bright iron L emission has enabled us to detect a reverberation lag of about 30 s between the direct X-ray continuum and its reflection from matter falling into the black hole. The observed reverberation timescale is comparable to the light-crossing time of the innermost radii around a supermassive black hole. The combination of spectral and timing data on 1H 0707-495 provides strong evidence that we are witnessing emission from matter within a gravitational radius, or a fraction of a light minute, from the event horizon of a rapidly spinning, massive black hole.
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Acknowledgements
A.C.F. thanks the Royal Society for support. This work is based on observations made with XMM-Newton, a European Space Agency (ESA) science mission with instruments and contributions directly funded by ESA member states and the USA (NASA). A.Z. acknowledges the support of the Algerian Higher Education Ministry and the UK Science and Technology Facilities Council (STFC). C.S.R., W.N.B., G.M., G.P. and R.C.R., and A.J.B. acknowledge support from the US National Science Foundation, NASA, the Spanish Ministerio de Ciencia e Innovacion, the French National Research Agency and the UK STFC for support, respectively.
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Fabian, A., Zoghbi, A., Ross, R. et al. Broad line emission from iron K- and L-shell transitions in the active galaxy 1H 0707-495. Nature 459, 540–542 (2009). https://doi.org/10.1038/nature08007
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DOI: https://doi.org/10.1038/nature08007
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