Symmetry Analysis of the Multi-band Optical Variability of BL LAC S5 0716+714 in Intranight and Longer Timescales

The well-sampled optical light curves of S5 0716+714 in BVRI bands spanning about 20 years were built. The variability asymmetry could provide independent constraints on physical models for blazars variability. To perform analyses of variability properties, individual flares were decomposed and fitted from the light curves with functions of exponential rise and decay. In order to investigate whether the short term variability (STV) and intraday variability (IDV) had different mechanisms of origin, the light curves of S5 0716+714 with different timescales were analyzed, respectively. Results indicate that both STV and IDV flares of S5 0716+714 are predominantly asymmetric profiles. And there also exist a very weak tendency of positive asymmetry in both timescales variabilities, i.e., rapid rises and gradual decays. The estimated sizes of emission region are 2.4 × 1016 ~ 3.3 × 1018 cm and 6.6 × 1014 ~ 4.8 × 1016 cm for STV and IDV, respectively. Based on the individual flares decomposed from STV and IDV light curves, the distribution of the peak flux and duration time of flares are consistent with log-normal and Gamma distributions. Minijet-in-a-jet model could interpret the lognormal distribution. Gamma distribution could demonstrate that the emission regions in the jet may be distributed in a Poisson way.