Continuum Reverberation Mapping of Accretion Disks Surrounding Supermassive Black Hole Binaries: Observational Signatures
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2025
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| author | Fu, Yi-Xin Li, Yan-Rong Wang, Jian-Min Horne, Keith Santisteban, Juan V. Hernández Vieliute, Roberta Edelson, Rick Liu, Tingting Brotherton, Michael S. Popović, Luka Č. Kovačević, Andjelka B. Zhai, Shuo |
| author_facet | Fu, Yi-Xin Li, Yan-Rong Wang, Jian-Min Horne, Keith Santisteban, Juan V. Hernández Vieliute, Roberta Edelson, Rick Liu, Tingting Brotherton, Michael S. Popović, Luka Č. Kovačević, Andjelka B. Zhai, Shuo |
| contents | It has remained challenging to reliably identify sub-parsec supermassive black hole binaries (SMBHBs), despite them being expected to be ubiquitous. We propose a new method using multi-band continuum reverberation mapping to identify low-mass-ratio SMBHBs in active galactic nuclei. The basic principle is that, due to the presence of a low-density cavity between the mini-disks and the circumbinary disk, the continuum emissions show a deficit at certain wavelengths, leading to a distinguishing feature in the relation between the inter-band time lag and wavelengths $τ(λ)$. Specifically, the relation appears flat at short wavelengths because of the truncated sizes of the mini-disks and transits to a power law $λ^{4/3}$ at long wavelength stemming from the circumbinary disk. This transition feature is distinct from the uniform relation $λ^{4/3}$ of the standard accretion disk around a single black hole. Using the lamp-post scenario and assuming that only the secondary black hole is active in a low-mass-ratio SMBHB, we design a simple continuum reverberation model to calculate the transfer function of the accretion disks and the resulting $τ(λ)$ relations for various SMBHB orbital parameters. The transition wavelength typically can lie at UV/optical bands, mainly depending on the total mass and orbital separation of the SMBHB. We apply our SMBHB model to the intensive multiwavelength monitoring data of the SMBHB candidate PG1302-102 and find that the SMBHB model can reproduce the inter-band time lags. Remarkably, the inferred total mass and orbital period from the SMBHB fitting are consistent with values derived from other independent methods. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_21671 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Continuum Reverberation Mapping of Accretion Disks Surrounding Supermassive Black Hole Binaries: Observational Signatures Fu, Yi-Xin Li, Yan-Rong Wang, Jian-Min Horne, Keith Santisteban, Juan V. Hernández Vieliute, Roberta Edelson, Rick Liu, Tingting Brotherton, Michael S. Popović, Luka Č. Kovačević, Andjelka B. Zhai, Shuo Astrophysics of Galaxies High Energy Astrophysical Phenomena It has remained challenging to reliably identify sub-parsec supermassive black hole binaries (SMBHBs), despite them being expected to be ubiquitous. We propose a new method using multi-band continuum reverberation mapping to identify low-mass-ratio SMBHBs in active galactic nuclei. The basic principle is that, due to the presence of a low-density cavity between the mini-disks and the circumbinary disk, the continuum emissions show a deficit at certain wavelengths, leading to a distinguishing feature in the relation between the inter-band time lag and wavelengths $τ(λ)$. Specifically, the relation appears flat at short wavelengths because of the truncated sizes of the mini-disks and transits to a power law $λ^{4/3}$ at long wavelength stemming from the circumbinary disk. This transition feature is distinct from the uniform relation $λ^{4/3}$ of the standard accretion disk around a single black hole. Using the lamp-post scenario and assuming that only the secondary black hole is active in a low-mass-ratio SMBHB, we design a simple continuum reverberation model to calculate the transfer function of the accretion disks and the resulting $τ(λ)$ relations for various SMBHB orbital parameters. The transition wavelength typically can lie at UV/optical bands, mainly depending on the total mass and orbital separation of the SMBHB. We apply our SMBHB model to the intensive multiwavelength monitoring data of the SMBHB candidate PG1302-102 and find that the SMBHB model can reproduce the inter-band time lags. Remarkably, the inferred total mass and orbital period from the SMBHB fitting are consistent with values derived from other independent methods. |
| title | Continuum Reverberation Mapping of Accretion Disks Surrounding Supermassive Black Hole Binaries: Observational Signatures |
| topic | Astrophysics of Galaxies High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2507.21671 |