An XMM-Newton Analysis of the Supermassive Black Hole Binary Candidate 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 $\Gamma =1.63_{-0.21}^{+0.20}$ and $N_{\text{H}}/10^{22}{\text{ cm}}^{-2}=17.9_{-2.4}^{+2.7}$ for the first epoch, and $\Gamma =1.46_{-0.24}^{+0.22}$ and $N_{\text{H}}/10^{22}{\text{ cm}}^{-2}=17.1_{-2.4}^{+2.7}$ 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.

13 pages, 4 figures, 3 tables, accepted for publication in ApJ

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