# Jet-powered Outflows in Supermassive Black Hole Binary Candidate SDSS J1048+0055

## TL;DR

This study used multi-frequency VLBI data to investigate the radio properties of the SMBH binary candidate SDSS J1048+0055, finding evidence against the binary interpretation of the radio components and suggesting a core-jet structure instead.

## Contribution

The paper provides detailed VLBI analysis that challenges the binary SMBH interpretation, favoring a core-jet scenario and clarifying the nature of the double-peaked emission lines.

## Key findings

- The brighter VLBI component shows flat spectrum and high brightness temperature.
- The apparent separation speed exceeds expected orbital motion, ruling out a binary core.
- The double-peaked lines may originate from jet interactions, not a binary SMBH.

## Abstract

The search and study of close pairs of supermassive black holes (SMBHs) is important in the study of galaxy mergers which can possibly trigger active galactic nucleus (AGN) activity, and in the context of their evolution into the gravitational wave emitting regime. The quasar SDSS~J1048+0055 was identified as a SMBH binary candidate based on the observed double-peaked \OIII$\lambda\lambda$4959,5007 emission lines and two distinct radio components separated by $\sim 20$~pc \citep{2004ApJ...604L..33Z}. To ascertain the binary nature of this source, we analyzed multi-frequency, multi-epoch very long baseline interferometry (VLBI) data to investigate its pc-scale radio properties. The source shows double components with the western feature being brighter than the eastern one. This brighter component has a brightness temperature of $\sim 10^{10}$~K, spectral index of $\alpha = -0.09 \pm 0.09$ (flat) and is indicative of mildly relativistic beaming. In contrast, the faint component has a lower brightness temperature of $\sim 10^{8-9}$~K and steep spectrum. These clues are consistent with a core--jet structure, moreover, the apparent separation speed between the two components is much higher than the expected orbital motion in a binary SMBH. Thus the present study excludes the association of the two VLBI components with the cores of a SMBH binary, although the SMBH binary possibility (e.g., a pair of radio-loud and radio-quiet AGNs) is not fully ruled out. In the single active galactic nucleus (AGN) scenario, the double-peaked optical emission lines can originate from the jet interacting with the narrow-line region as indicated by a change in the jet direction at $\sim$ 140 pc.