The Estimation of Fundamental Physics Parameters for Fermi-LAT Blazars

Abstract

Aiming to delineate the physical framework of blazars, we present an effective method to estimate four important parameters based on the idea proposed by \citet{BK95}, including the upper limit of central black hole mass $M$, the Doppler factor $δ$, the distance along the axis to the site of the $γ$-ray production $d$ (which then can be transformed into the location of $γ$-ray-emitting region $R_γ$) and the propagation angle with respect to the axis of the accretion disk $Φ$. To do so, we adopt an identical sample with 809 {\it Fermi}-LAT-detected blazars which had been compiled in \citet{Pei20PASA}. These four derived parameters stepping onto the stage may shed new light on our knowledge regarding $γ$-ray blazars. With regard to the paper of \citet{BK95}, we obtain several new perspectives, mainly in: (1) putting forward an updated demarcation between BL Lacs and FSRQs based on the relation between broad-line region luminosity and disk luminosity both measured in Eddington units, i.e., $L_{\rm disk}/L_{\rm Edd}=4.68\times10^{-3}$, indicating that there are some differences between BL Lacs and FSRQs on the accretion power in the disk; (2) proposing that there is a so-called `appareling zone', a potential transition field between BL Lacs and FSRQs where the changing-look blazars perhaps reside; (3) the location of $γ$-ray emission region is principally constrained outside the broad-line region, and for some BL Lacs are also away from the dusty molecular torus, which means the importance of emission components in the jet.