A comprehensive view of PKS 2155-304 from 2008 to 2023 through a multi-epoch modeling of its spectral energy distributions

Abstract

We present a detailed investigation of the temporal and spectral evolution of the emission from the blazar PKS 2155-304, a high-synchrotron-peaked (HSP) blazar. Using $\gamma$-ray, X-ray, optical/UV, and infrared data assembled from the Markarian Multiwavelength Data Center, we constructed multi-band light curves and temporally resolved spectral energy distributions (SEDs) of PKS 2155-304 to probe the origin of its emission. The light curves show significant variability, with fractional variability peaking at 0.75 in X-rays, 0.4 in the optical/UV, and 0.65 in $\gamma$-ray band-consistent with expectations for HSPs. Segmenting the $\gamma$-ray light curve with Bayesian blocks, we defined 253 time-resolved epochs with adequate multi-band coverage and categorized them into quiescent states (QS), multiwavelength flares (MWF), $\gamma$-ray flares ($\gamma$F), X-ray flares (XF), and optical/UV flares (OUF). Each SED is modeled within a synchrotron self-Compton (SSC) framework that self-consistently evolves particle injection and cooling; a neural-network surrogate is used to accelerate parameter inference. Kolmogorov-Smirnov tests reveal state-dependent parameter variations relative to QS: (i) during MWF, the magnetic field B, electron luminosity $L_{e}$, maximum electron Lorentz factor $\gamma_{max}$, and Doppler factor $\delta$ differ significantly; (ii) during $\gamma$F, a harder electron index p is estimated; (iii) XF shows higher B and $\gamma_{max}$ with a more compact emitting region; and (IV) during OUF, changes in B, $L_{e}$, $\gamma_{max}$, $\delta$, and p are found while the emitting-zone size remains approximately constant. The jet power is electron-dominated (magnetic-to-electron power ratio $\eta_{B}\simeq0.09-0.17$), with $\eta_{B}$ rising during XF. These results suggest that variations in acceleration efficiency and magnetization drive band-dependent flaring in PKS 2155-304.