Estimates of Emission-Region Locations of Fermi Flat-Spectrum Radio Quasars

Abstract

We have studied the location of emission regions through modeling the quasi-simultaneous multifrequency spectral energy distributions of 21 Fermi flat-spectrum radio quasars (FSRQs) in the frame of a multicomponent one-zone leptonic model. In our calculations, we took the detailed broad line region (BLR) structure into account, and discussed the effect of the uncertainty of the BLR structure on constraining the location of the emission regions for each FSRQ; besides, we also included both the internal and the external absorptions. Our results indicate that: (1) the contribution of the external Compton-BLR component to the γ-ray emission is important, and the energy density of external target-photon fields depends on the location of the emission region, which can be derived by reproducing the observed γ-ray emission; (2) the emission regions of FSRQs with relatively low accretion-disk luminosity lie in the region of (7.9×10¹⁶-1.3×10¹⁸ cm (300-4300 Schwarzschild radii) from central black hole, and for FSRQs with high accretion-disk luminosity, the emission regions are located in a larger region of (2.6×10¹⁷-4.2×10¹⁸) cm (300-5600 Schwarzschild radii).