Blob Ejection from Advection-dominated Accretion Flow: Observational Consequences

There is increasing evidence for the presence of an optically thin advection-dominated accretion flow (ADAF) in low-luminosity active galactic nuclei and radio-loud quasars. The present Letter is devoted to exploring the fate of a blob ejected from an ADAF and to discussing its observational consequences. It is inevitable for the ejected blob to drastically expand into its surroundings. Consequently, it is expected that a group of relativistic electrons will be accelerated, which may lead to nonthermal flares since a strong shock will be formed by the interaction between the blob and its surroundings. Then the blob cools down efficiently, leading to the appearance of recombination lines about 10⁵ s after its ejection from an ADAF. We apply this model to NGC 4258 for some observational prediction and to PKS 2149-306 for the explanation of observational evidence. Future simultaneous observations of recombination X-ray lines and continuum emission are strongly desired for testing the present model.