SDSS J153636.22+044127.0 and its analogues: shocked outflows, not active
  binary black holes
  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
(Boroson \& Lauer 2009). Here, we show the follow-up optical and near-infrared
spectral observations of SDSS J153636.22+044127.0 and its analogues. 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 $\lambda$10830 profile and the
abnormally strong emission of the hydrogen Pa$\beta$ blue system oppose the
binary proposal. We suggest that these unique broad lines arise from the AGN
emission-line region and the shock-heated outflowing gases rather than a binary
system of two active black holes.
