الفهرس 
The Emission Mechanisms in BlazarsOnly 14 pages are availabe for public view
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Abstract
The Fermi large area telescope (LAT), has been harvesting blazar photons in a continuous manner for more than dozen years now. Through these accumulated observations, we are beginning to probe the structure of the long time variation of the emission intensity. A question of particular interest concerns the nature of the repeated flaring: whether it is always best characterized by a stochastic process, or if clear examples of quasi-periodic signals exist. This is currently a contentious issue that is starting to be seriously tackled by the high energy astrophysics community. An important observational feature of Fermi-LAT blazars is their variability, which remarkably occasionally shows quasi-periodic oscillations; a characteristic that could convey information regarding the emission mechanisms from their central engines, as well as the possibility of observing merging systems. The present work searches for 0.1–100 GeV γ-ray periodic modulations in distant flat-spectrum radio quasars, using the Fermi-LAT pass 8 data for a time span of about 14 yr. The search for such signals in the γ-ray light curves was carried out using four time-series analysis tools: the Generalized Lomb-Scargle periodogram (GLSP), the weighted wavelet z-transform (WWZ), the REDFIT algorithm, as well as the auto-correlation function. We reported six blazars with possible quasi-periodicities, four of them were found with periodic signals that are identified for the first time and the other two sources, PKS 0426–380 and PKS 2255-282, were confirmed with their previously reported signals in the literature. Considering a super binary black hole system (SBBHS) model, the parameters of the binary for each object were estimated; namely, a binary separation , total mass , and decay time of the gravitational wave emission . It is possible that these quasiperiodicities may be understood in the context of the standard cosmological model of involving hierarchical structure formation.