An XMM-Newton Analysis of the Supermassive Black Hole Binary Candidate MCG+11--11--032

TL;DR

This study uses two epochs of XMM-Newton data to investigate the supermassive black hole binary candidate MCG+11--11--032, finding no evidence of a double Fe Kα line and supporting a single AGN scenario.

Contribution

It provides new XMM-Newton observations that challenge previous claims of a binary black hole system in MCG+11--11--032.

Findings

No evidence for a double iron line in either observation.

Spectral parameters are consistent with prior datasets.

Supports the single AGN scenario for MCG+11--11--032.

Abstract

We investigate the possibility of a binary supermassive black hole system at the center of MCG+11--11--032, a local (z = 0.036) Seyfert 2 galaxy. Prior work with stacked Swift/XRT spectra suggested the presence of two Fe K$\alpha$ lines (at 6.16 keV and 6.56 keV) with 2$\sigma$ confidence. This could be consistent with a prediction of several hydrodynamical models, in which each black hole hosts a mini-disk and contributes one Doppler-shifted Fe K$\alpha$ line to the total spectrum. Another study using a single exposure from Chandra/ACIS did not find evidence for a double line. Here, we conduct follow-up with two epochs of XMM-Newton/EPIC data spaced $\sim$6 months apart. After fitting our spectra with models from the previous two studies, we do not find evidence for a double iron line in either observation. Our best-fit model yields $\Gamma = 1.63^{+0.20}_{-0.21}$ and $N_\text{H}/10^{22} \text{ cm}^{-2} = 17.9^{+2.7}_{-2.4}$ for the first epoch, and $\Gamma = 1.46^{+0.22}_{-0.24}$ and $N_\text{H}/10^{22} \text{ cm}^{-2} = 17.1^{+2.7}_{-2.4}$ for the second. We compare our spectral parameters with those derived in past work on this source, finding broad agreement with prior datasets. Lastly, we discuss the properties of MCG+11--11--032 alongside samples of Seyfert 2 galaxies from the literature, finding that it is consistent with this population and the single AGN scenario.