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Peer-reviewedCC BY 4.0The Astrophysical Journal

Migration Traps as Variability Attractors. I. Optical/UV Signatures of Embedded Stellar-mass Black Holes in Active Galactic Nucleus Disks

  • Jing-Tong Xing1
  • Tong Liu1
  • Mouyuan Sun1
  • Ya-Ping Li1,2
  • Shuying Zhou1
  • Zhen-Yi Cai3
  • Da-Bin Lin4
  • Jian-Min Wang2,5,6
6 affiliations
  1. 1Xiamen University
  2. 2Chinese Academy of Sciences
  3. 3University of Science and Technology of China
  4. 4Guangxi University
  5. 5University of Chinese Academy of Sciences
  6. 6National Astronomical Observatory of China
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Abstract

We investigate whether embedded stellar-mass black holes (sBHs) in active galactic nucleus (AGN) disks can leave observable optical/UV variability signatures through migration-trap-driven magnetic heating. This mechanism operates when sBHs migrating toward torque-balance radii pile up near migration traps, triggering localized, stochastic magnetic reconnection that heats the disk atmosphere. It is potentially important because it provides a physical source of noncoronal disk heating and directly links optical/UV continuum variability to otherwise hidden compact-object populations. By coupling a one-dimensional sBH population synthesis model with a corona-heated accretion-disk reprocessing variability framework, we show that migration traps concentrate sBHs at preferred radii and generate localized, stochastic reconnection heating. The resulting heating is self-regulated: sBH pile-ups enhance the reconnection rate, while gap opening reduces the local gas density and partially suppresses the reconnection power. This heating produces excess short-timescale optical/UV variability, flattened short-term structure functions, and deviations from the standard τ ∝ λ 4/3 lag-wavelength relation, which describes the time delay between variability at different wavelengths for a standard thin accretion disk. These signatures are strongest at low-to-moderate Eddington ratios, and related observations could provide indirect evidence for embedded compact-object populations in AGN disks.

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Cite

BibTeXRIS
BibTeX
@article{xing2026migration,
  title = {{Migration Traps as Variability Attractors. I. Optical/UV Signatures of Embedded Stellar-mass Black Holes in Active Galactic Nucleus Disks}},
  author = {Jing-Tong Xing and Tong Liu and Mouyuan Sun and Ya-Ping Li and Shuying Zhou and Zhen-Yi Cai and Da-Bin Lin and Jian-Min Wang},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aeaa4f},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aeaa4f},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Migration Traps as Variability Attractors. I. Optical/UV Signatures of Embedded Stellar-mass Black Holes in Active Galactic Nucleus Disks
AU  - Jing-Tong Xing
AU  - Tong Liu
AU  - Mouyuan Sun
AU  - Ya-Ping Li
AU  - Shuying Zhou
AU  - Zhen-Yi Cai
AU  - Da-Bin Lin
AU  - Jian-Min Wang
PY  - 2026
DA  - 2026/10/13
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aeaa4f
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aeaa4f
AB  - We investigate whether embedded stellar-mass black holes (sBHs) in active galactic nucleus (AGN) disks can leave observable optical/UV variability signatures through migration-trap-driven magnetic heating. This mechanism operates when sBHs migrating toward torque-balance radii pile up near migration traps, triggering localized, stochastic magnetic reconnection that heats the disk atmosphere. It is potentially important because it provides a physical source of noncoronal disk heating and directly links optical/UV continuum variability to otherwise hidden compact-object populations. By coupling a one-dimensional sBH population synthesis model with a corona-heated accretion-disk reprocessing variability framework, we show that migration traps concentrate sBHs at preferred radii and generate localized, stochastic reconnection heating. The resulting heating is self-regulated: sBH pile-ups enhance the reconnection rate, while gap opening reduces the local gas density and partially suppresses the reconnection power. This heating produces excess short-timescale optical/UV variability, flattened short-term structure functions, and deviations from the standard τ ∝ λ 4/3 lag-wavelength relation, which describes the time delay between variability at different wavelengths for a standard thin accretion disk. These signatures are strongest at low-to-moderate Eddington ratios, and related observations could provide indirect evidence for embedded compact-object populations in AGN disks.
SN  - 0004-637X
SN  - 1538-4357
ER  -