THE RADIO-LOUD NARROW-LINE QUASAR SDSS J172206.03+565451.6

摘要

We report identification of the radio-loud narrow-line quasar SDSS J172206.03+565451.6, which we found in the course of a search for radio-loud narrow-line active galactic nuclei (AGNs). SDSS J172206.03+565451.6 is only about the fourth securely identified radio-loud narrow-line quasar and the second-most radio loud, with a radio index R_(1.4) ≈ 100-700. Its black hole mass, M_(BH) approx = (2-3) x 10~7 solar mass estimated from Hβ line width and 5100 A luminosity, is unusually small given its radio loudness, and the combination of mass and radio index puts SDSS J172206.03+ 565451.6 in a scarcely populated region of M_(BH)-R diagrams. SDSS J172206.03+565451.6 is a classical narrow-line Seyfert 1-type object with FWHM_(Hβ) approx = 1490 km s~(-1) an intensity ratio of [O III]/Hβ approx = 0.7, and Fe II emission complexes with Fe II λ4570/Hβ approx = 0.7. The ionization parameter of its narrow-line region, estimated from the line ratio [O II]/[O III], is similar to Seyferts, and its high ratio of [Ne V]/[Ne III] indicates a strong EUV-to-soft X-ray excess. We advertise the combined usage of [O II]/[O III] and [Ne V]/[Ne III] diagrams as a useful diagnostic tool to estimate ionization parameters and to constrain the EUV—soft X-ray continuum shape relatively independently from other parameters.