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

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 diskembedded 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 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.