Long-Term and Flares Variability of Fermi LAT FSRQ 4 C + 21 . 35

The current study presents a long-term light curve (LC) of the flat spectrum radio quasar (FSRQ) 4C +21.35 (also known as PKS 1222+216, z=0.432) as observed by the Fermi Large Area Telescope (LAT) during the first seven years of the mission with weekly time binning in the energy range 0.2–50 GeV. The highest weekly integral flux reached on MJD = 55365 (2010 June 18). 4C +21.35 exhibited during this period two major flares (flare I during MJD = 55296 – 55405 and flare II during MJD = 56961 56984). For flare states, the variability of the source emission was studied with 12hour time binning in two energy bands 0.2 – 0.8 GeV and 0.8 – 50 GeV. Three different statistical methods, the structure functions (SF), auto-correlation functions (ACF), and fast Fourier transformer (FFT) were used to study the time scales. For the seven year-weekly binning light curve, an 18-week time scale was observed. Flare I seems to have the same time scales for both energy ranges. Therefore, the outbursts during flare I may have come from the same emission mechanism/s; CCF between the two energy bands also emphasized it. Flare II did not give significant results. CCF illustrated a 6.5-day time lag that indicates the emission mechanism of the low energy band came before the high energy one with 6.5 day with a typical physical process.