TARCHI, ANDREAANDREATARCHIHenkel, C.C.HenkelChiaberge, M.M.ChiabergeMenten, K. M.K. M.MentenBrunthaler, A.A.BrunthalerMOSCADELLI, LucaLucaMOSCADELLI2023-01-042023-01-042005978-1-4020-3038-3978-1-4020-3831-0http://hdl.handle.net/20.500.12386/32833We report the first detection of a water megamaser in a radio-loud galaxy, 3C 403, and present a follow-up study using the VLA. 3C 403 has been observed as a part of a small sample of FR II galaxies with evidence of nuclear obscuration. The isotropic luminosity of the maser is ∼1200 Lʘ. With a recessional velocity of cz ∼- 17680 km s<SUP>-1</SUP> it is the most distant water maser so far reported. The line arises from the densest (>10<SUP>8</SUP> cm <SUP>-3</SUP>) interstellar gas component ever observed in a radio-loud galaxy. Two spectral features are identified, likely bracketing the systemic velocity of the galaxy. Our interferometric data clearly indicate that these arise from a location within 0.1″ (≈110 pc) from the active galactic nucleus. We conclude that the maser spots are most likely associated with the tangentially seen parts of a nuclear accretion disk, while an association with dense warm gas interacting with the radio jets cannot yet be ruled out entirely.ELETTRONICOenConference paper10.1007/1-4020-3831-3_14https://link.springer.com/book/10.1007/1-4020-3831-32005dmgp.book..117TFIS/05 - ASTRONOMIA E ASTROFISICA