2025ApJ...991...78X

The physics-determined broadband spectral energy distributions (SEDs) of blazars have been widely used to study their properties during their flaring/outburst states, while the nonflaring state takes up most of their lifetime and the general property of blazars has been barely discussed. In this work, for the first time, we used the archival data and employed the physics-determined SED processing method to form approximately average-state SEDs for 513 Fermi bright BL Lacs. In general, we found that the magnetic field (B) is weaker than those obtained for the flaring/outburst state by nearly 1 order of magnitude, and the dissipation region size (R) is larger than those obtained for the flaring/outburst state, suggesting that the dissipation region could be more extended and less magnetized. A correlation between the synchrotron self-Compton peak frequency (${\mathrm{log}}\,{\nu }_{{{\rm{ssc}}}}$) and the synchrotron peak frequency (${\mathrm{log}}\,{\nu }_{{{\rm{sy}}}}$) suggests that the inverse Compton scattering of higher-synchrotron-peaked BL Lacs suffers a significant Klein-Nishina (KN) suppression; we quantified the condition of KN suppression by determining the critical synchrotron peak frequency (${\nu }_{{{\rm{sy}}}^{{\rm{c}}}}$) and found 359 out of 513 sources in our sample suffer KN suppression. Furthermore, our analysis of the relationship between synchrotron curvature (1/b_sy) and ${\mathrm{log}}\,{\nu }_{{{\rm{sy}}}}$ indicates that the energy-dependent probability acceleration mechanism may dominate the particle acceleration in BL Lac jets.