The Spectrum and Polarization Variation Study at Short-term Timescales for Four Luminous Blazars

Abstract Blazars exhibit complex variability of fluxes, spectra, and polarizations, whose underlying mechanisms remain an open question. We analyze short-term spectral and polarization variability in four luminous flat-spectrum radio quasars (3C 454.3, B2 1633+382, PKS 1510–08, CTA 102) using optical photometric, polarimetric, and spectroscopic data from the Steward Observatory (2008–2018). We find that optical flux correlates positively with polarization degree in 12 of 13 flare segments. Three sources demonstrate redder-when-brighter trend, contrasting with CTA 102’s distinctive bluer-when-brighter behavior during its 2016–2017 outburst. The BWB trend could be explained by the peak-frequency modulation within the shock-in-jet model. Polarization angle trajectories show diverse rotation patterns, including clockwise, anticlockwise, and oscillations, that currently lack a universal theoretical explanation. Nevertheless, a unified two-component model successfully explains both spectral trends and correlations between the polarization and fluxes through varying jet-to-disk flux ratios, providing critical constraints on blazar physics.