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

ABSTRACT We investigate the temporal and spectral evolution of the blazar PKS 2155−304 using gamma-ray, X-ray, optical/ultraviolet (UV), and infrared data from the Markarian Multiwavelength Data Center. We constructed multiband light curves and time-resolved spectral energy distributions (SEDs) to probe the origin of its emission. The light curves show strong variability, with the largest amplitudes in the soft-medium X-rays and notable variations also in the$\gamma$ gamma-ray band. Based on the$\gamma$ gamma-ray light curve we defined 253 epochs and categorized them into quiescent states (QS), multiwavelength flares (MWF),$\gamma$ gamma-ray flares ($\gamma$F), X-ray flares (XF), and optical/UV flares (OUF). Each SED is modelled within a one-zone synchrotron self-Compton framework using a neural-network surrogate for fast parameter inference. Kolmogorov–Smirnov tests reveal state-dependent parameter variations relative to QS: (i) during MWF, the magnetic field B, electron luminosity $L_{\rm e}$, maximum electron Lorentz factor $\gamma _{\rm max}$, and Doppler factor $\delta$ differ significantly; (ii) during $\gamma$F, a harder electron index p is estimated; (iii) XF shows higher B and $\gamma _{\rm max}$ with a more compact emitting region; and (IV) during OUF, changes in B, $L_{\rm e}$, $\gamma _{\rm max}$, $\delta$, and p are found while the emitting-zone size remains approximately constant. The jet power is electron-dominated (magnetic-to-electron power ratio $\eta _{\rm B}\simeq 0.09$–0.17, subject to uncertainties introduced by the assumption $\gamma _{\min }=100$), with $\eta _{\rm B}$ rising during XF. These results suggest that variations in acceleration efficiency and magnetization drive band-dependent flaring in PKS 2155−304.