2025PASP..137j4101Y

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.