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

TL;DR

This paper investigates the observational signatures of accretion-modified stars within AGN disks, analyzing their spectral energy distributions and light curves across different disk regions to understand their transient behaviors.

Contribution

It provides a detailed modeling of multiwavelength emissions and light curves of AMSs in various AGN disk regions, highlighting their transient features and observational signatures.

Findings

UV flares with luminosity ~10^{44} erg/s in the middle region

X-ray synchrotron peaks at ~10^{43} and 10^{42} erg/s in middle and inner regions

Gamma-ray inverse Compton luminosity spans 10^{42} to 10^{43} erg/s with peaks at ~10 MeV and GeV bands

Abstract

Stars and compact objects embedded in accretion disks of active galactic nuclei (AGNs), dubbed as ``accretion-modified star" (AMS), 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 growth of the AMSs during the shift inwards is considered. We calculate their multiwavelength spectral energy distributions (SEDs) and thermal light curves. Our results reveal that the thermal luminosity of Bondi explosion occurring in the middle region leads to UV flares with a luminosity of $\sim 10^{44}\rm \,erg\,s^{-1}$. The synchrotron radiation of Bondi explosion in the middle and inner regions peaks at the X-ray band with luminosities of $\sim 10^{43}$ and $\sim 10^{42}\rm \,erg\,s^{-1}$, respectively. The $\gamma$-ray luminosity of inverse Compton radiation spans from $10^{42}$ to $10^{43}\rm \,erg\,s^{-1}$ peaked at $\sim 10\,$MeV (outer region) and $\sim$ GeV (middle and inner regions) bands. The observable flares of AMS in the middle region exhibits 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 provides valuable insights into the various astronomical transient timescales associated with AGNs.