The Medium and Long Period Broad Band Spectral Index Characteristics of Flat Spectrum Radio Quasar 3C 454.3

Blazar is a very active AGN. Studying its broad band spectral index is the effective method to understand its internal structure and radiation mechanism. The data in this paper adopts the SMARTS database that has been published so far. There are 682 groups of observation data with quasi-simultaneity in B, V, R, J, K bands. The characteristics of its broad band spectral index are studied using LombScargle Periodogram (LSP) method. The results show that 3C 454.3 optical and infrared band light variations are positively correlated; there are two dominant periods in optical and infrared band, which are about 1.2 yr and 4.5 yr, respectively; in the double black hole structure model, the mass ratio of double black holes is about 2/1.