The averaged broadband spectral energy distribution study of Fermi bright BL Lac objects

Abstract

The physics-determined broadband spectral energy distributions (SEDs) of blazars have been widely used to study the property during their flaring/outburst states, while the non-flaring 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 \textit{Fermi} bright BL Lacs. In general, we found that the magnetic field ($B$) is weaker than those obtained for flaring/outburst state by nearly one order of magnitude, and the dissipation region size ($R$) is larger than those obtained for flaring/outburst state, suggesting that the dissipation region could be more extend and less magnetized. A correlation between the synchrotron-self Compton (SSC) peak frequency ($\log \nu_{\rm ssc}$) against the synchrotron peak frequency ($\log \nu_{\rm sy}$) suggest that the inverse Compton scattering of HBLs suffer 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 ($1/b_{\rm sy}$) and $\log \nu_{\rm sy}$ indicates that the energy-dependent probability acceleration (EDPA) mechanism may dominate the particle acceleration in BL Lac jets.