Variation of Broad Emission Lines from QSOs with Optical/UV Periodicity to Test the Interpretation of Supermassive Binary Black Holes

Abstract

Quasars with periodic light curves are considered as candidates of supermassive binary black hole (BBH) systems. One way for further confirmations may be searching for other characteristic signatures, such as those in their broad emission lines (BELs), if any, which require a thorough understanding on the response of BELs to the BBH systems. In Ji et al. ( 2021), we have investigated the response of circumbinary broad line region (BLR) to the central active secondary black hole under the relativistic Doppler boosting (BBH-DB) and intrinsic variation (BBH-IntDB) dominant mechanisms for continuum variation by assuming the middle plane of the BLR aligned with the BBH orbital plane. In this paper, we explore how the BEL profiles vary when the BLR is misaligned from the BBH orbital plane with different offset angles under both the BBH-DB and BBH-IntDB scenarios. Given a fixed inclination angle of the BBH orbital plane viewed in edge-on and similar continuum light curves produced by the two scenarios, increasing offset angles make the initial opening angle of the circumbinary BLR enlarged due to orbital precession caused by the BBH system, especially for clouds in the inner region, which result in Lorentz-like BEL profiles for the BBH-DB model but still Gaussian-like profiles for the BBH-IntDB model at the vertical BLR case. The amplitude of profile variations decrease with increasing offset angles for the BBH-DB scenario, while keep nearly constant for the BBH-IntDB scenario, since the Doppler boosting effect is motion direction preferred but the intrinsic variation is radiated isotropically. If the circumbinary BLR is composed of a coplanar and a vertical components with their number of clouds following the mass ratio of the BBHs, then the bi-BLR features are more significant for the BBH-IntDB model that require larger mass ratio to generate similar continuum variation than the BBH-DB model.

Detection of eccentric close-binary supermassive black holes with incomplete interferometric data

“…Farris et al 2014). Furthermore, the accretion rate is higher on the component with the lowest mass in unequalmass CB-SMBHs (Artymowicz & Lubow 1994;Hayasaki et al 2007;Roedig et al 2011;Farris et al 2014), potentially making it more luminous than the primary (Bogdanović et al 2022;Ji et al 2021). Additionally, mass accretion is higher onto the secondary SMBH because it moves closer to the edge of the CBD.…”

“…We assume that the secondary SMBH has a higher accretion rate and is more luminous than the primary (see e.g. Dexter et al 2020;Ji et al 2021), which is broadly referred to hereafter as the 'active SMBH'. As the main unknown in this setup is where the NIR continuous emission comes from and how it evolves over the binary motion, we look at two scenarios as prescribed by Dexter et al (2020).…”

Detection of eccentric close-binary supermassive black holes with incomplete interferometric data

“…Farris et al 2014). Furthermore, the accretion rate is higher on the component with the lowest mass in unequalmass CB-SMBHs (Artymowicz & Lubow 1994;Hayasaki et al 2007;Roedig et al 2011;Farris et al 2014), potentially making it more luminous than the primary (Bogdanović et al 2021;Ji et al 2021). Additionally, mass accretion is higher onto the secondary SMBH because it moves closer to the edge of the CBD.…”

The Gravitational-wave physics II: Progress

“…We have investigated the detection of individual SMBBHs by current and future PTAs and its possible cosmological application to constrain cosmological parameters [634][635][636]. We have found a number of SMBBH candidates [637,638], investigated the detailed observational properties of some SMBBH candidates [639,640], and introduced several new methods to identify BBH candidates and distinguish it from alternative interpretations [641][642][643][644], investigated the cosmic evolution of SMBBHs and predicted the SGWBs resulting from inspiralling SMBBHs and SMBBH merger rate [645].…”