Observable signatures of stellar-mass black holes in active galactic nuclei

TL;DR

This paper proposes that electromagnetic signatures from shocks around jets launched by stellar-mass black holes in AGN disks could serve as observable evidence of these embedded black holes, with detectable thermal and non-thermal emissions across multiple bands.

Contribution

It introduces a novel model predicting observable breakout emissions from shocks around jets from embedded stellar-mass black holes in AGN disks, linking theoretical predictions to potential detections.

Findings

Breakout emission characterized by luminous thermal X-ray emission.

Bright broadband non-thermal emission from infrared to gamma-ray.

Flare durations vary from 10^3 to 10^6 seconds depending on black hole's distance.

Abstract

Stellar-mass black holes (BHs) are predicted to be embedded in the disks of active galactic nuclei (AGN) 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 the majority of the highly super-Eddington flow reaches the BH, produces a strong jet, and the jet produces feedback that shuts off accretion and thus leads to episodic flaring. While these assumptions are highly uncertain at present, they predict a breakout emission characterized by luminous thermal emission in the X-ray bands, and bright, broadband non-thermal 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 $r \sim 0.01-1$ pc. This emission can be discovered by current and future infrared, optical, and X-ray wide-field surveys and monitoring campaigns of nearby AGNs.