Black hole masses and Doppler factors of γ -ray active galactic nuclei
Abstract
The sizes of the broad-line regions (BLRs) in
γ
-ray active galactic nuclei (AGNs) are estimated from their optical continuum luminosity by using the empirical relation between
R
BLR
and
L
λ,opt
. Using the broad emission line data, we derive the photon energy density in the relativistic blobs near the massive black holes in AGNs. We calculate the power of the broad-line photons Compton up-scattered by the relativistic electrons in the blobs. Compared with observed
γ
-ray emission data, the Doppler factors
δ
of the blobs for a sample of 36
γ
-ray AGNs are derived, which are in the range of
∼3−17
. We estimate the central black hole masses of these
γ
-ray AGNs from the sizes of the BLR and the broad line widths. It is found that the black hole masses are in the range of
∼
10
8
−
10
10
M
⊙
. A significant correlation is found between the Doppler factor
δ
and the core dominance parameter
R
. The results are consistent with the external radiation Compton (ERC) models for
γ
-ray emission from AGNs. The soft seed photons are probably from the broad-line regions.