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Low Luminosity Active Galactic Nuclei (LLAGNs) possess the characteristicfeatures of more luminous Active Galactic Nuclei (AGNs) but exhibit a muchlower nuclear Halpha luminosity than their more luminous counterparts. M87 (NGC4486) and Centaurus A (NGC 5128, CenA) are well-studied nearby LLAGNs. As anadditional feature they show gamma-radiation up to TeV (10^{12}eV) energies,but the origin of this radiation is not resolved. The coincident observation ofa radio and TeV flare in M87 suggests that the TeV radiation is produced withinaround 50-100 gravitational radii of the central supermassive black hole,depending on the assumed value of the mass of the black hole. Strong radiationfields can be produced in the central region of an (LL)AGN, e.g., by theaccretion flow around the black hole, the jet plasma, or stars closely orbitingthe black hole. These radiation fields can lead to the absorption of emittedTeV photons, and in fact high optical depths of such fields can make TeVdetection from inner regions impossible. In this paper we consider theaccretion flow around the black hole as the most prominent source for such aradiation field and we accordingly calculate the probability for absorption ofTeV photons produced near the black holes in M87 and CenA assuming a lowluminosity Shakura-Sunyaev Disk (SSD). We find that the results are verydifferent for between the two LLAGNs. While the inner region of M87 istransparent for TeV radiation up to 15TeV, the optical depth in CenA is >> 1,leading to an absorption of TeV photons that might be produced near the centralblack hole. These results imply either that the TeV gamma production sites andprocesses are different for both sources, or that LLAGN black holes do notaccrete (at least only) in form of a low luminosity SSD.

Internal gamma gamma-opacity in Active Galactic Nuclei and the consequences for the TeV observations of M87 and Cen A