Characterizing the Emission Region Properties of Blazars

Abstract

Studies and constraints on the emission region are crucial to the blazar radiation mechanism. Yet previous works have mainly focused on individual sources. In this work, we make use of the largest and the latest spectral energy distribution fitting results in the literature to statistically study the blazar emission region properties in the framework of a one-zone leptonic model. Our results reveal: (1) that flat-spectrum radio quasars (FSRQs) show lower electron energy (γ p ≲ 1.6 × 103) than BL Lacertae objects (BL Lacs) and tend to have a stronger magnetic field (B) and smaller electron-to-magnetic energy ratio (U e/U B) than BL Lacs; (2) we find that the electromagnetic equipartition would rather happen in the jets of BL Lacs than happen in the jets of FSRQs; (3) there are 682 blazars with a magnetic field weaker than the critical value for generating the Kelvin–Helmholtz instability, thus one-third of the blazars in our sample are able to produce this instability; and (4) the distance (d em) between the emission region and the central black hole is on the scale of ∼0.1 pc, so the location of the emission region may be evenly distributed inside and outside the broad-line region.