A Test of External Compton Models for Gamma‐Ray Active Galactic Nuclei

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There is clear evidence that the gamma-ray emission from active galactic nuclei (AGNs) can be attributed to inverse Compton scatterings in the relativistic blobs near the massive black holes. If the soft seed photons are from the regions outside the blobs, a linear relation between (vF(v,gamma)/vF(v,syn)u(*))(1/(1+alpha)) and the Doppler factor delta is expected, where vF(v,gamma) and vF(v,syn) are monochromatic gamma-ray and synchrotron fluxes, respectively, and u(*) is the energy density of soft seed photons. We estimate the soft photon energy density in the relativistic blobs contributed by the broadline regions (BLRs) in these gamma-ray AGNs using their broad-line emission data. The Doppler factors delta are derived from their radio core and X-ray emission data, based on the assumption that the X-ray emission is produced through synchrotron self-Compton (SSC) scatterings. We find two nearly linear correlations: (vF(v,gamma)/vF(opt)u(*))1/(1+alpha) proportional to delta(1.09) and (vF(v,gamma)/vF(IR)u(*))(1/(1+alpha)) proportional to delta(1.20), which are roughly consistent with the linear correlation predicted by the theoretical model for external Compton scatterings. Our results imply that the soft seed photons are predominantly from the BLRs in these gamma-ray AGNs.