| Active galactic nucleus(AGN),powered by accretion onto the supermassive black holes,is one of the most special object in the universe.There are violent phenomena and extreme physical processes.AGN is often used as the main probe to study the evolution of the large-scale structure of the universe,the formation and evolution of galaxies,and the acceleration process of cosmic particles.Blazars,as the most extreme type of active galactic nucleus,which has relativistic jet at a very small angle with the observer’s line of sight.The broadband electromagnetic radiation of blazars is dominated by non-thermal(NT)emission.They usually show observational characteristics of high polarization,rapid variability and high luminosity etc.However,the generation mechanism of the jet,the acceleration and emission mechanism of the high-energy particles in the jet,and the nature of the variability of the flare need still to further study.In the thesis,the high energy y-ray data of blazars S5 0716+714 and CTA 102 were analyzed in detail.The analysis methods of Bayesian Blocks(BB)algorithm,discrete correlation function,power spectrum density,and normality test were employed to study the properties of the y-ray variability and spectrum properties.Based on these observational characteristics,the jet parameters and the physical mechanisms of the yray variability were constrained.The main results are in the following:The γ-ray light curve of S5 0716+714 in the 8 years observation shows six γ-ray outburst phases,with peak fluxes above 4×10-7 ph cm-2 s-1.The characteristics of the flux distribution with the short timescale,the symmetry of time structure of light curve,and the spectral evolution were analyzed.We obtained the y-ray Doppler factor,the size and distance of the emission region of δmin≥4.8-5.4、R～2.0-3.5×1015 cm、rγ～0.0016-0.85 pc,respectively.These values imply that the emission region lies near or beyond the outer edge of the BLR and the y-ray emission regions vary from one flare to another.The shortest variability timescale is found to be 1.5±0.3 hour with a peak flux above 100 MeV of(26.8±6.9)×10-7 ph cm-2 s-1.The five highest-energy photons,with E>100 GeV,imply that the high-energy emission from this source may originate from a moving emission region in a helical path upstream in the jet.No hint of periodic modulations has been detected for the light curve of S5 0716+714.The 10 years observation of CTA 102 shows three γ-ray flare phases.Their flux and index distributions with the short timescale show the double log-normal distribution.The shortest rise and decay timescales are 0.71±0.05 hr and 0.90±0.07 hr,respectively.The y-ray Doppler factor,the viewing angle of the jet,the magnetic field and the distance of the emission region from all flares identified by the BB method are δmin≥3.9-24.1、θjet≥2.91°-4.11°、BJ≥1.2-1.9 G、dγ<19.6 pc.The minimum penetration heights(zmin)are larger than the size of the BLR(Rblr=0.1 pc).These analyses imply that the intrinsic particle acceleration or escape time-scales are linear Gaussian variations,and the short timescale flare of source is originate from the magnetic reconnection,also implying that the location of the γ-ray emission region of CTA 102 may lie in the inner jet upstream of the radio core.Moreover,the flare doesn’t show that a "hard lag" should lead to a counter-clockwise hysteresis loop,while a "soft lag" may result in a clockwise hysteresis loop.Four different models,power-law(PL),log parabola(LP),broken PL(BPL),and a PL with an exponential cut-off(PLEC)were used to fit the spectra.The long-term and short-term spectra of the two sources display obvious break/curvature phenomenon.The break energies of S5 0716+714 are in the range of 0.93-6.90 GeV,and those of CTA 102 is 5.9-14.8 GeV.The present models,like "cooling break/curvature","absorption effect","double components model","line emission" are seems not to explain this feature.Although a continuous curved electron energy distribution can produce spectral cut-off,which is not been fully confirmed. |
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