2004ApJ...604L..33Z

We report the discovery of a possible close binary system of quasars in SDSS J1048+0055. The [O III] λλ4959, 5007 emission lines are clearly double-peaked, and two discrete radio sources with a projected physical separation of ∼20 pc are found in the Very Long Baseline Array milliarcsecond resolution image at 8.4 GHz. Each of the [O III] λλ4959, 5007 doublets and Hβ can be well modeled by two Gaussians, and the line ratio [O III] λ5007/Hβ∼7 is typical of Seyfert 2 galaxies. No broad component of Hβ was detected, and its [O III] λ5007 luminosity, L_[OIII]_~9.2x10⁴² ergs/s, is comparable to luminous quasars and is a few x10 more luminous than typical Seyfert galaxies. One natural interpretation is that SDSS J1048+0055 contains two close quasar-like nuclei, and the broad-line region around them is obscured. Other possible models are also discussed. We suggest that a double-peaked narrow emission line profile may be an effective way of selecting candidates of binary black holes with intermediate separation.