Optical Variation And Energy Spectrum Analysis Of Blazars

Based on the 1.26m Guangzhou University infrared/optical telescope（NGT）,we monitored the blazar 1ES 2200+420 in 14 nights during the period from 2018 September 5 to 2020 September 20.During the monitoring,we ob-tained 5352 observations,among which,at three bands,there are 1763（g band）,1667（r band）,and 1922（i band）observations.We collected the spectral energy spectrum（SED）data of blazar 1ES 2200+420 from SSDC,meanwhile we gathered the available data of 334 other blazars from NED,Using the above observations,we obtained the following results:（1）Based on the analyses of the C-test and F-test,we found that there are 2 nights（g band）,4 nights（r band）,and 3 nights（i band）lying intra-day variabilities（IDVs）.Based on the discrete correlation function method（DCF）and the power spectrum analysis（PSA）,we obtained the average period of intra-day variability（IDV）,P=215.1±3.6 min.IDV period is generally considered to come from the innermost orbit of the blazar,and it can help us to study some physical properties of the blazar,such as we used the IDV period to calculate the central black hole mass,M_I=0.83×10⁸（M_⊙）～5.04×10⁸（M_⊙）.（2）We used the DCF method to study the time-delay between the multi band,and the result show that:between the g and r band,τ_grare-4.4 and-1.7 min;between the g and i band,τ_giare-6.7 and-5.1 min;between the i and r band,τ_irare 1.1 and6.9 min.These results imply that the gri emissions should have the same physical origin,but the emission regions are different.We used three methods for analyzing and obtain four long periods,P₁=0.34±0.04 yr,P₂=0.68±0.6 yr,P₃=4.84±0.72yr,and P₄=24.83±5.98 yr.（3）We used the leptonic one-zone synchrotron and inverse Compton（SSC）mod-el to model the spectral energy distribution of 1ES 2200+420.At the gri band,the relations between spectral index and flux density show the brighter when bluer behav-ior（BWB）.（4）There are strong correlation,non-correlation and strong anti-correlation for the LSP,ISP and HSP between the curvature b and logν_p,respectively.