Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Observational Characteristics in Different Regions of the Disks

Abstract

Stars and compact objects embedded in accretion disks of active galactic nuclei (AGNs), dubbed accretion-modified stars (AMSs), often experience hyper-Eddington accretion in the dense gas environment, resulting in powerful outflows as the Bondi explosion and formation of cavities. The varying gas properties across different regions of the AGN disk can give rise to diverse and intriguing phenomena. In this paper, we conduct a study on the characteristics of AMSs situated in the outer, middle, and inner regions of the AGN disk, where the growth of the AMSs during the shift inward is considered. We calculate their multiwavelength spectral energy distributions (SEDs) and thermal light curves. Our results reveal that the thermal luminosity of the Bondi explosion occurring in the middle region leads to UV flares with a luminosity of ∼10 ^44 erg s ^−1 . The synchrotron radiation of Bondi explosion in the middle and inner regions peaks at the X-ray band with luminosities of ∼10 ^43 and ∼10 ^42 erg s ^−1 , respectively. The γ -ray luminosity of inverse Compton radiation spans from 10 ^42 –10 ^43 erg s ^−1 peaked at the ∼10 MeV (outer region) and ∼GeV (middle and inner regions) bands. The observable flares of AMS in the middle region exhibit a slow rise and rapid Gaussian decay with a duration of months, while in the inner region, it exhibits a fast rise and slow Gaussian decay with a duration of several hours. These various SED and light-curve features provide valuable insights into the various astronomical transient timescales associated with AGNs.

Keywords

• Active galactic nuclei
• Bondi accretion
• Stellar mass black holes
• Supermassive black holes
• Gamma-rays
• Light curves