Long-term multiband correlation study and spectral energy distribution modeling of blazar 3C 454.3

We analyzed the multiband and long-term light curves of blazar 3C 454.3 over a time span of more than 10 yr. The discrete correlation functions (DCFs) between the γ-rays (Fermi-LAT) and the U and V bands (Swift) show simultaneous variations above the 99% confidence level. The DCFs between the X-ray band and the ultraviolet/U bands (Swift-UVW2, Swift-UVW1) are correlated over the 95% confidence level, with the X-ray variations leading by 98 d. The observed X-ray emission might not come from the same region as the γ-rays. For the studied time range, we identify four flare states and one quiescent state in the γ-ray light curve. With a synchrotron self-Compton + external Compton (EC) model, the spectral energy distributions (SEDs) of the five quasi-simultaneous observed states are modeled to discuss the underlying reasons for the flares. The EC soft photons could originate from the broad-line region (BLR) rather than from the dusty torus for the quiescent and four activity states. This indicates that the γ-ray radiation area may be located inside the BLR. From the quiescent state to the flare states, the fitting results show that N0, γmax, γbr, and δ increase, while B and R decrease. The reproduction of the SEDs implies that the increase in the bulk Lorentz factor and the emitted electron power might be the primary reason for the γ-ray flares.