Multiband Optical Variability of the Blazar 3C 454.3 on Diverse Timescales

TL;DR

This study presents a comprehensive long-term analysis of the optical variability of blazar 3C 454.3 over two decades, revealing spectral trends, bimodal spectral index distribution, and co-spatial emission across optical bands.

Contribution

First long-term multi-band optical variability analysis of 3C 454.3, combining data from multiple sources to reveal spectral and flux variability patterns.

Findings

Redder when brighter trend stabilizes at a brightness cutoff.

Bimodal spectral index distribution correlates with flux states.

Intra-day variability observed in six out of nine light curves.

Abstract

Due to its peculiar and highly variable nature, the blazar 3C 454.3 has been extensively monitored by the WEBT team. Here, we present for the first time these long-term optical flux and color variability results using data acquired in B, V, R, and I bands over a time span of $\sim$ 2 decades. We include data from WEBT collaborators and public archives such as SMARTS, Steward Observatory, and ZTF. The data are binned and segmented to study the source over this long term when more regular sampling was available. During our study, the long-term spectral variability reveals a redder when brighter (RWB) trend, which, however, stabilizes at a particular brightness cutoff $\sim$ 14.5 mag in the I-band, after which it saturates and evolves into a complex state. This trend indicates increasing jet emission dominance over accretion disk emission until jet emission completely dominates. Plots of the spectral index variation (following $F_{\nu} \propto \nu^{-\alpha}$) reveal a bimodal distribution using a one-day binning. These correlate with two extreme phases of 3C 454.3, an outburst or high flux state and quiescent or low flux state, which are respectively jet and accretion disk dominated. We have also conducted intra-day variability studies of nine light curves and found that six of them are variable. Discrete Correlation Function (DCF) analysis between different optical waveband pairs peak at zero lags, indicating co-spatial emission in different optical bands.