2021MNRAS.504.2509W

Blazars are variable targets in the sky, whose variation mechanism remains an open question. In this work, we make a comprehensive study of the variation phenomena of the spectral index and polarization degree to deeply understand the variation mechanism of B2 1633+382 (4C 38.41). We use the local cross-correlation function to perform a correlation analysis between multiwavelength light curves. We find that both the γ-ray and the optical V band are correlated with the 15-GHz radio at beyond the 3σ confidence level. Based on the lag analysis, the emitting regions of the γ-ray and optical are located at 14.2_–2.4⁺⁰ and 14.2_–8.3^+8.3 pc upstream of the core region of the15-GHz radio, and are far away from the broad-line region. The broad lines in the spectrum indicate the existence of an accretion disc component in the radiation. Thus, we consider a two-component model, which includes the relative constant background component and the varying jet component to study the variation behaviours. The Markov Chain Monte Carlo procedure is adopted to study the physical parameters of the jet and the background components. To some extent, the study of normalized residuals indicates that the two-component model fits better than the linear fitting model. The jet with a helical magnetic field is promising for explaining the variation, and the shock-in-jet model is not completely ruled out.