2009ApJ...699.2002B

In this paper, we revisit gamma-ray-emitting region for 10 GeV-1 TeV gamma rays from 3C 279 through studying the photon-photon absorption optical depth due to the diffuse radiation of the broad-line region (BLR) and the extragalactic background light (EBL). Based on the power-law spectrum detected by MAGIC, the preabsorbed spectra are inferred by correcting the photon-photon absorption on the diffuse photons of the BLR (internal absorption) and the EBL (external absorption). Position of gamma-ray-emitting region R_γ determines the relative contributions of this two diffuse radiations to the total absorption. Our results indicate that R_γ may be within the BLR shell for 3C 279, likely closer to the inner radius, which is consistent with our previous results. This is neither consistent with the suggestions of Böttcher et al., that very high energy (VHE) gamma-ray emission is produced far outside the BLR, nor with the assumptions of Tavecchio and Mazin, that VHE gamma-ray-emitting region is inside the BLR cavity. R_γ is a key physical quantity that could set some constraints on emission mechanisms that produce the VHE gamma rays from 3C 279. Observations of Fermi-Large Area Telescope, MAGIC, H.E.S.S., and VERITAS in the near future could give more constraints on the position of gamma-ray-emitting region relative to the BLR.