# SDSS J153636.22+044127.0 and its analogues: shocked outflows, not active binary black holes

## TL;DR

This study challenges the binary black hole interpretation of SDSS J153636.22+044127.0, proposing instead that its peculiar emission lines result from shocked outflows in the active galactic nucleus.

## Contribution

The paper provides follow-up spectral observations that refute the binary black hole hypothesis and suggest shock-heated outflows as the origin of the emission lines.

## Key findings

- Invariance of emission lines over time contradicts binary black hole models.
- Absence of blue system in He I λ10830 profile supports non-binary origin.
- Strong hydrogen Paβ blue emission indicates shock-heated outflows.

## Abstract

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.