The First Spectroscopically Resolved Sub-Parsec Orbit of a Supermassive Binary Black Hole

Abstract

One of the most intriguing scenarios proposed to explain how active galactic nuclei are triggered involves the existence of a supermassive binary black hole system in their cores. Here we present an observational evidence for the first spectroscopically resolved sub-parsec orbit of a such system in the core of Seyfert galaxy NGC 4151. Using a method similar to those typically applied for spectroscopic binary stars we obtained radial velocity curves of the supermassive binary system, from which we calculated orbital elements and made estimates about the masses of components. Our analysis shows that periodic variations in the light and radial velocity curves can be accounted for an eccentric, sub-parsec Keplerian orbit of a 15.9-year period. The flux maximum in the lightcurve correspond to the approaching phase of a secondary component towards the observer. According to the obtained results we speculate that the periodic variations in the observed Hα line shape and flux are due to shock waves generated by the supersonic motion of the components through the surrounding medium. Given the large observational effort needed to reveal this spectroscopically resolved binary orbital motion we suggest that many such systems may exist in similar objects even if they are hard to find. Detecting more of them will provide us with insight into black hole mass growth process.

Spectroscopic Indication of a Centi-Parsec Supermassive Black Hole Binary in the Galactic Center of Ngc 5548

“…Another nearby case is NGC4151 at ∼14 Mpc (z = 0.003319), which, interestingly, was also found to have a similar period of ∼15 yr in flux variations (Pacholczyk et al 1983;Guo et al 2006). The SMBHB hypothesis in NGC4151 was subsequently reported by Bon et al (2012) based on an analysis of the Hα emission line. Below we use the extensive spectroscopic monitoring database over four decades (much longer than the time span of the database for NGC 4151) to provide more evidence for an SMBHB in NGC5548.…”

“…However, the identification of subparsec SMBHBs is particularly challenging because these small separations at cosmic distance are well below the angular resolving power of the current and even most future powerful telescopes. Searching for the spectroscopic signatures is certainly an ideal solution (e.g., Bon et al 2012;Eracleous et al 2012;Popović 2012;Shen et al 2013;Liu et al 2014;Yan et al 2015 and references therein), although robust, conclusive evidence for sub-parsec SMBHBs remains rare. If both components of the binary contain a broad-line region (BLR), monitoring secular changes in the intensity and velocity of the line-emitting clouds offers a promising avenue to identify gravitationally bound, sub-parsec SMBHB pairs in their last phase of dynamical evolution.…”

Long-Term Monitoring of the Broad-Line Region Properties in a Selected Sample of AGN

“…For example, in case of 3C 390.3 it is clear that the BLR is following the accretion disk geometry (Popović et al, 2011), whereas in case of the other double-peak line emitter Arp 102B this is maybe not the case . Also, the Seyfert galaxies NGC 4151 and NGC 5548 could host a binary SMBH with two separate BLR (Bon et al, 2012(Bon et al, , 2016Li et al, 2016), which puts more uncertainty on their mass estimates from reverberation mapping. Finally, the quasar E1821+643 is much below the theoretical radius-luminosity relation predicted by the photoionization theory (R BLR ∝ L 0.5 ), and very low-variable AGN in the optical lines and continuum, therefore this SMBH mass estimate is also more uncertain.…”

Oscillatory patterns in the light curves of five long-term monitored type 1 active galactic nuclei

“…To address such situation, we proposed a hybrid method to detect unknown weak periodic signals in the AGN light curves, which is a modification of the recently proposed timing methods used Hα Dietrich et al 1998Shapovalova et al 2010Sergeev et al 2011Dietrich et al 2012Afanasiev et al 2015 50000 51000 52000 53000 54000 55000 56000 JD -2400000 in geophysics (Pering et al 2014) and acoustics research (Yang & Tse 2005 Kaspi et al 1996Shapovalova et al 2010Bon et al 2012 47000 48000 49000 50000 51000 52000 53000 54000 JD -2400000 for investigation of transient or unstable periodic phenomena), and Spearman correlation technique that accounts for non-linearity and variable amplitude of the wavelet coefficients.…”

“…Due to complexity of this object, it might be useful to search for periodicity information hidden in the other wavebands, i. e. the continuum 1370 Å, Lyα and CIV lines collected by IUE satellite from 1978-1992(Wamsteker et al 1997) and from 1994December to 1996March (O' Brien et al 1998 (iv) For NGC 4151, Fig. 3, the light curves include observations from Kaspi et al (1996Kaspi et al ( , covering period over two months in 1993, from Shapovalova et al (2010bShapovalova et al ( , covering period 1996Shapovalova et al ( -2006, and finally we added two observations presented in Bon et al (2012Bon et al ( , one from 1986Bon et al ( , and other from 1989; (v) Up to now, for E1821+643 the only information available are fluxes obtained from its the first long term monitoring campaign conducted by Shapovalova et al (2016) …”