2019ApJ...877...33Z

The binary emission-line system, particularly the binary broad-line emission system, is considered the most effective indicator of the black hole binary. A plausible example of such a system, SDSS J153636.22+044127.0, was reported as the first known object with two hydrogen Balmer broad-line systems, which are interpreted to be the result of broad-line regions around a pair of black holes. Here, we show the follow-up optical and near-infrared spectral observations of SDSS J153636.22+044127.0 and its analogs. In these objects, the broad hydrogen Balmer and Paschen, He I, and Mg II lines share the same peculiar emission-line profile (including a blue system, a red system, and a double-peaked disk-line component); however, the invariance in the large time interval, the absence of the blue system in He I λ10830 profile, and the abnormally strong emission of the hydrogen Paβ blue system oppose the binary proposal. We suggest that these unique broad lines arise from the active galactic nucleus emission-line region and the shock-heated outflowing gases rather than a binary system of two active black holes.