Swift data hint at a binary supermassive black hole candidate at sub-parsec separation

Journal
Date Issued
2018
Author(s)
•
CICONE, CLAUDIA
•
•
•
•
Ballo, L.
•
•
•
•
Vignali, C.
•
Zaino, A.
•
Matzeu, G. A.
•
DOI
Abstract
Dual/binary supermassive black hole (SMBH) systems are the inevitable consequence of the current Lambda cold dark matter cosmological paradigm. In this context, we discuss here the properties of MCG+11-11-032, a local (z = 0.0362) Seyfert 2 galaxy. This source was proposed as a dual active galactic nucleus candidate on the basis of the presence of double-peaked [O III] emission lines in its optical spectrum. MCG+11-11-032 is also an X-ray variable source and was observed several times by the Swift X-ray Telescope (XRT) on time scales from days to years. In this work, we analyze the SDSS-DR13 spectrum and find evidence for double-peaked profiles in all the strongest narrow emission lines. We also study the XRT light curve and unveil the presence of an alternating behavior of the intrinsic 0.3-10 keV flux, while the 123-month Swift BAT light curve supports the presence of almost regular peaks and dips almost every 25 months. In addition, the XRT spectrum suggests for the presence of two narrow emission lines with rest-frame energies of E ∼ 6.16 keV and E ∼ 6.56 keV. Although by considering only the optical emission lines, different physical mechanisms may be invoked to explain the kinematical properties, the X-ray results are most naturally explained by the presence of a binary SMBH in the center of this source. In particular, we evidence a remarkable agreement between the putative SMBH pair orbital velocity derived from the BAT light curve and the velocity offset derived by the rest-frame ∆E between the two X-ray line peaks in the XRT spectrum (i.e. ∆v ∼ 0.06c).
Volume
479
Issue
3
Start page
3804
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2018MNRAS.479.3804S
Rights
open.access
File(s)
Loading...
Thumbnail Image
Name

Severgnini_1806.10150.pdf

Description
preprint
Size

656.07 KB

Format

Adobe PDF

Checksum (MD5)

8e2946dad809697a14aa68d837156fb0

Loading...
Thumbnail Image
Name

sty1699.pdf

Description
Pdf editoriale
Size

663.36 KB

Format

Adobe PDF

Checksum (MD5)

84854010b886d02a1406075f25e92a18