Issue |
A&A
Volume 690, October 2024
|
|
---|---|---|
Article Number | L2 | |
Number of page(s) | 7 | |
Section | Letters to the Editor | |
DOI | https://doi.org/10.1051/0004-6361/202451901 | |
Published online | 27 September 2024 |
Letter to the Editor
Evidence for gravitational self-lensing of the central supermassive black hole binary in the Seyfert galaxy NGC 1566
1
Institut für Astrophysik und Geophysik, Universität Göttingen, Friedrich-Hund Platz 1, 37077 Göttingen, Germany
2
Department of Physics, Faculty of Natural Sciences, University of Haifa, Haifa 3498838, Israel
3
Haifa Research Center for Theoretical Physics and Astrophysics, University of Haifa, Haifa 3498838, Israel
Received:
16
August
2024
Accepted:
11
September
2024
Context. It is generally accepted that all massive galaxies host supermassive black holes (BHs) in their center and that mergers of two galaxies lead to the formation of BH binaries. The most interesting among them comprise the mergers in their final state, that is to say with parsec (3.2 light years) or sub-parsec orbital separations. It is possible to detect these systems with binary self-lensing.
Aims. Here we report the potential detection of a central supermassive BH binary in the active galaxy (AGN) NGC 1566 based on a microlensing outburst. The light curve of the outburst – based on observations with the All Sky Automated Survey for SuperNovae – lasted from the beginning of 2017 until the beginning of 2020. The steep symmetric light curve as well as its shape look very different with respect to normal random variations in AGN.
Results. However, the observations could be easily reproduced with a best-fit standard microlensing light curve. Based on the light curve, we derived a characteristic timescale of 155 days. During the outburst, the continuum as well as the broad line intensities varied; however, the narrow emission lines did not. This is an indication that the lensing object orbits the AGN nucleus between the broad line region (BLR) and the narrow line region (NLR), that is, at a distance on the order of 250 light days. The light curve can be reproduced by a lens with a BH mass of 5 × 105 M⊙. This implies a mass ratio to the central AGN on the order of 1–10.
Key words: accretion, accretion disks / gravitational lensing: micro / galaxies: active / galaxies: individual: NGC 1566 / quasars: supermassive black holes
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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