Interpreting the variation phenomena of B2 1633+382 via the two-component model

TL;DR

This study investigates the variability mechanisms of blazar B2 1633+382 by analyzing multi-wavelength data and applying a two-component model, revealing the locations of emission regions and supporting a helical magnetic field in the jet.

Contribution

It introduces a two-component model combined with MCMC analysis to better understand blazar variability, especially in spectral index and polarization degree.

Findings

Emission regions are located over 14 pc from the radio core.

The two-component model fits the data better than linear models.

Helical magnetic fields in jets may explain observed variations.

Abstract

Blazars are variable targets in the sky, whose variation mechanism remains an open question. In this work, we make a comprehensive study on the variation phenomena of the spectral index and polarization degree (PD) to deeply understand the variation mechanism of B2 1633+382 (4C 38.41). We use the local cross-correlation function (LCCF) to perform the correlation analysis between multi-wavelength light curves. We find that both $\gamma$-ray and optical $V$-band are correlated with the radio 15 GHz at the beyond 3$\sigma$ confidence level. Based on the lag analysis, the emitting regions of $\gamma$-ray and optical locate at $14.2_{-2.4}^{+0}$ pc and $14.2_{-8.3}^{+8.3}$ pc upstream of the core region of radio 15 GHz, and are far away from the broad-line region (BLR). The broad lines in the spectrum indicate the existence of the accretion disk component in the radiation. Thus, we consider the two-component (TC) model, which includes the relative constant background component and the varying jet component to study the variation behaviors. The Markov Chain Monte Carlo (MCMC) 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 TC model fits better than the linear fitting model. The jet with helical magnetic field is hopeful to explain the variation, and the shock in jet model is not completely ruled out.