paper

Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Slowly Transient Appearance

arXiv:2103.07708 · doi:10.3847/2041-8213/abee81

Abstract

Compact objects are expected to exist in the accretion disks of supermassive black holes (SMBHs) in active galactic nuclei (AGNs), and in the presence of such a dense environment (), they will form a new kind of stellar population denoted as Accretion-Modified Stars (AMSs). This hypothesis is supported by recent LIGO/Virgo detection of the mergers of very high-mass stellar binary black holes (BHs). We show that the TZOs will be trapped by the SMBH-disk within a typical AGN lifetime. In the context of SMBH-disks, the rates of Bondi accretion onto BHs are , where is the Eddington luminosity and is the speed of light. Outflows developed from the hyper-Eddington accretion strongly impact the Bondi sphere and induce episodic accretion. We show that the hyper-Eddington accretion will be halted after an accretion interval of s, where $m_{1}=m_{\bullet}/10\sunm$ is the BH mass. The kinetic energy of the outflows accumulated during is equivalent to 10 supernovae driving an explosion of the Bondi sphere and developing blast waves. We demonstrate that a synchrotron flare from relativistic electrons accelerated by the blast waves peaks in the soft X-ray band (keV), significantly contributing to the radio, optical, UV, and soft X-ray emission of typical radio-quiet quasars. External inverse Compton scattering of the electrons peaks around GeV and is detectable through {\it Fermi}-LAT. The flare, decaying with with a few months, will appear as a slowly varying transient. The flares, occurring at a rate of a few per year in radio-quiet quasars, provide a new mechanism for explaining AGN variability.

arXiv comment10 pages, 3 figures, accepted

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