الفهرس 
Active galactic nuclei
Fermi-LAT detectorFermi-LAT detectorOnly 14 pages are availabe for public view
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Abstract
Blazars as a subclass of Active Galactic Nuclei (AGN) are distinguished by erratic variability at all energies on a wide range of time scales. The observed spectra are dominated by the beamed and highly variable emission of the innermost parts of relativistic jets. Source variability appears as an increase in the source flux, known as flares. Flux variability is expected to provide important clues about the emission mechanism(s) inside the radiating source region. In this work, statistical analysis of large data set was performed to reveal the properties of GeV blazars selected from Fermi LAT catalog. The long-term variability of these sources was studied using 7 years of Fermi-LAT data in the energy range 200 MeV–50 GeV collected starting August 2008 and extending until August 2015. The flare states of each source have been studied with short time binning and the energy was divided to two energy bands E=200-800 MeV and E=0.8-50 GeV as well. Three different statistical methods were used to study the time/frequency scales; the structure functions (SF), auto-correlation functions (ACF) and fast Fourier transforms (FFT). Cross correlation function (CCF) between the two energy bands can tell if the flare state happened simultaneously and/or with time lag between the two energy ranges that help to put constraints on the emission region. One of the most remarkable results is the time delay ±7.5 day with the fourth flare of 3C 454.3 and the 6.5 days from 4C +21.35 during flare II. The latter indicates the flare state came with the low energy band then with higher one. Photon (gamma-ray) Index Γ distributions for each energy and for both flare and quiescent states have been studied by using different statistical tests. Shapiro-Wilk (SW) and Kolmogorov-Smirnov (K-S) normality tests were used to check the results for conformance to a normal distribution. One-way analysis of variance (ANOVA) test was used to check the hypothesis that the means of each two groups of gamma-ray index distributions are derived from the same population. With Γ distribution study one can illustrate if the flare states dominantly came with low or/and high energy and the possibility of finding the source at very high energy campaigns as well as confirm whether the source obey simple power law or broken power law. For instance, the results of the first source indicate that this source 3C 454.3 has to be a bracken power law and the flare states emitted in GeV energy ranges and are presumably observed at VHE (E > 100 GeV) campaigns.