Long-Term and Flares Variability of Fermi LAT FSRQ 4C

Abstract

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 2.647 x 10(-6) phcm(-2)s(-1) 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 12-hour 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.