Abstract Stellar-mass black holes (BHs) are predicted to be embedded in the disks of active galactic nuclei (AGNs) due to gravitational drag and in situ star formation. However, clear evidence for AGN disk-embedded BHs is currently lacking. Here, as possible electromagnetic signatures of these BHs, we investigate breakout emission from shocks emerging around Blandford–Znajek jets launched from accreting BHs in AGN disks. We assume that most of the highly super-Eddington flow reaches the BH and produces a strong jet, and the jet produces feedback that shuts off accretion and thus leads to episodic flaring. These assumptions, while poorly understood at present, yield observable consequences that can probe the presence of AGN-embedded BHs as well as the accretion process itself. They predict a breakout emission characterized by luminous thermal emission in the X-ray bands and bright broadband nonthermal emission from the infrared to the gamma-ray bands. The flare duration depends on the BH’s distance r from the central supermassive BH, varying between 10 3 –10 6 s for r ∼ 0.01–1 pc. This emission can be discovered by current and future infrared, optical, and X-ray wide-field surveys and monitoring campaigns of nearby AGNs.
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This content will become publicly available on June 1, 2024
Observable Signature of Merging Stellar-mass Black Holes in Active Galactic Nuclei
Abstract The origin of stellar-mass black hole mergers discovered through gravitational waves is being widely debated. Mergers in the disks of active galactic nuclei (AGNs) represent a promising source of origin, with possible observational clues in the gravitational-wave data. Beyond gravitational waves, a unique signature of AGN-assisted mergers is electromagnetic emission from the accreting black holes. Here we show that jets launched by accreting black holes merging in an AGN disk can be detected as peculiar transients by infrared, optical, and X-ray observatories. We further show that this emission mechanism can explain the possible associations between gravitational-wave events and the optical transient ZTF 19abanrhr and the proposed gamma-ray counterparts GW150914-GBM and LVT151012-GBM. We demonstrate how these associations, if genuine, can be used to reconstruct the properties of these events’ environments. Searching for infrared and X-ray counterparts to similar electromagnetic transients in the future, once host galaxies are localized by optical observations, could provide a smoking-gun signature of the mergers’ AGN origin.
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- Award ID(s):
- 2006839
- NSF-PAR ID:
- 10433008
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 950
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 13
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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