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# Direct evidence of non-disk optical continuum emission around an active black hole

## Abstract

Accretion onto black holes is key to their growth over cosmic time1, especially during the active galactic nuclei phase when the inflowing material forms a radiatively efficient accretion disk2. To probe the disk, indirect imaging methods such as reverberation mapping3,4,5,6 and microlensing7,8 are required. Recent findings suggest that the disk may be larger than theoretical predictions by a factor of a few4,6,9, thus casting doubt on our understanding of accretion in the general astrophysical context. Whether new physics is implied10,11,12 or poorly understood biases are in effect5,6,13,14 is a longstanding question. Here, we report new reverberation data based on a unique narrowband-imaging design15, and argue that time delays between adjacent optical bands are primarily associated with the reprocessing of light by a farther away under-appreciated non-disk component. This component is associated with high-density photoionized material that is uplifted from the outer accretion disk, probably by radiation-pressure force on dust, and thus may represent the long-sought origin of the broad-line region16. Our findings suggest that the optical phenomenology of some active galactic nuclei may be substantially affected by non-disk continuum emission with implications for measuring the fundamental properties of black holes and their active environs over cosmic time.

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## Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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## Acknowledgements

We thank D. Maoz for continuous support of the project at the Wise Observatory, and S. Niv for enabling the robotic use of the C18 telescope. This work was partly supported by grants 950/15 from the Israeli Science Foundation and 3555/14-1 from the Deutsche Forschungsgemeinschaft. Computations on the Hive computer cluster at the University of Haifa are partly supported by Israeli Science Foundation grant 2155/15.

## Author information

Authors

### Contributions

D.C. conceived the project, post-processed the light curves, carried out time-series analyses and photoionization calculations, and wrote the paper. F.P.N. acquired the data, reduced them, carried out flux variation gradient calculations and time-series analyses, and contributed to writing the paper. S.K. assisted with the data reduction and time-series analyses, and provided technical support of telescope operations.

### Corresponding authors

Correspondence to Doron Chelouche or Francisco Pozo Nuñez.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

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## Supplementary information

### Supplementary Information

Supplementary Figures 1–10, Supplementary Tables 1–2, Supplementary References 1–3

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Chelouche, D., Pozo Nuñez, F. & Kaspi, S. Direct evidence of non-disk optical continuum emission around an active black hole. Nat Astron 3, 251–257 (2019). https://doi.org/10.1038/s41550-018-0659-x

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• DOI: https://doi.org/10.1038/s41550-018-0659-x