Search

We conduct a systematic search for quasars with periodic variations from the archival photometric data of the Zwicky Transient Facility by cross-matching with the quasar catalogues of the Sloan Digital Sky Survey and Véron-Cetty and Véron. We first select out 184 primitive periodic candidates using the generalized Lomb–Scargle periodogram and autocorrelation function and then estimate their statistical significance of periodicity based on two red-noise models, i.e. damped random walk (DRW) and single power-law (SPL) models. As such, we finally identify 106 (DRW) and 86 (SPL) candidates with the most significant periodic variations out of 143 700 quasars. We further compare DRW and SPL models using Bayes factors, which indicate a relative preference of the SPL model for our primitive sample. We thus adopt the candidates identified with SPL as the final sample and summarize its basic properties. We extend the light curves of the selected candidates by supplying other archival survey data to verify their periodicity. However, only three candidates (with 6–8 cycles of periods) meet the selection criteria. This result clearly implies that, instead of being strictly periodic, the variability must be quasi-periodic or caused by stochastic red-noise. This exerts a challenge to the existing search approaches and calls for developing new effective methods. [ABSTRACT FROM AUTHOR]

We performed a rigorous reverberation-mapping analysis of the broad-line region (BLR) in a highly accreting (L / L Edd = 0.74–3.4) active galactic nucleus, Markarian 142 (Mrk 142), for the first time using concurrent observations of the inner accretion disk and the BLR to determine a time lag for the H β λ 4861 emission relative to the ultraviolet (UV) continuum variations. We used continuum data taken with the Niel Gehrels Swift Observatory in the UVW 2 band, and the Las Cumbres Observatory, Dan Zowada Memorial Observatory, and Liverpool Telescope in the g band, as part of the broader Mrk 142 multiwavelength monitoring campaign in 2019. We obtained new spectroscopic observations covering the H β broad emission line in the optical from the Gemini North Telescope and the Lijiang 2.4 m Telescope for a total of 102 epochs (over a period of 8 months) contemporaneous to the continuum data. Our primary result states a UV-to-H β time lag of 8.68 − 0.72 + 0.75 days in Mrk 142 obtained from light-curve analysis with a Python-based running optimal average algorithm. We placed our new measurements for Mrk 142 on the optical and UV radius–luminosity relations for NGC 5548 to understand the nature of the continuum driver. The positions of Mrk 142 on the scaling relations suggest that UV is closer to the "true" driving continuum than the optical. Furthermore, we obtain log (M • / M ⊙) = 6.32 ± 0.29 assuming UV as the primary driving continuum. [ABSTRACT FROM AUTHOR]

We compile optical and mid-infrared light curves from the time-domain surveys (i.e. CRTS, PTF, ZTF, and ASAS-SN) and Wide-field Infrared Survey Explorer (WISE) archive for a selected sample of active galactic nuclei (AGNs) with Hβ reverberation mapping (RM) measurements. We measure the time lags (and thus torus sizes) of W 1 (∼3.4  |$\mu$| m) and W 2 (∼4.6  |$\mu$| m) band light curves relative to the optical one using the MICA method. Through Hβ RM, the sample has well-measured AGN properties, therefore allowing us to reliably constrain the relations between torus sizes and AGN properties. We perform linear regressions for the relations between torus sizes and 5100 Å luminosities (⁠|$R\propto L_{5100}^{\beta }$|) in two cases: β = 0.5 and β set free. The latter case yields β ≈ 0.37 ± 0.028 for both W 1 and W 2 bands, shallower than the expected value of 0.5, possibly due to the dependence of torus size on accretion rate. For β = 0.5, by combining with the previous K band RM measurements, we obtain the characteristic broad-line region (BLR) and tours sizes following R BLR: RK : R W 1: R W 2 = 1.0:6.2:9.2:11.2. We investigate the deviations of the W 1 and W 2 band observed torus sizes from the corresponding best-fitting relations (with β = 0.5) and find that they both are correlated with accretion rate. As the accretion rate increases, the torus sizes tend to be shortened compared to the anticipated sizes from the best-fitting relations, similar to the behaviour found in BLRs. Such behaviours can be explained by the self-shadowing effect of slim discs. This is further supported by ratios of the W 1 and W 2 band torus sizes to BLR sizes, which do not show significant correlations with AGN properties. [ABSTRACT FROM AUTHOR]

There are increasing interests in binary supermassive black holes (SMBHs), but merging binaries with separations smaller than |$\sim 1\,$|  light-days (⁠|$\sim 10^{2}\,$| gravitational radii for 108 M⊙), which are rapidly evolving under control of gravitational waves, are elusive in observations. In this paper, we discuss fates of mini-discs around component SMBHs for three regimes: (1) low rates (advection-dominated accretion flows: ADAFs); (2) intermediate rates; (3) super-Eddington accretion rates. Mini-discs with intermediate rates are undergoing evaporation through thermal conduction of hot corona forming a hybrid radial structure. When the binary orbital periods are shorter than sound propagation time-scales of the evaporated mini-discs, a new instability, denoted as sound instability, arises because the discs will be highly twisted so that they are destroyed. We demonstrate a critical separation of A crit(∼102 R g) from the sound instability of the mini-discs and the cavity is full of hot gas. For those binaries, component SMBHs are accreting with Bondi mode in the ADAF regime, showing periodic variations resulting from Doppler boosting effects in radio from the ADAFs due to orbital motion. In the mean while, the circumbinary discs (CBDs) are still not hot enough (ultraviolet deficit) to generate photons to ionize gas for broad emission lines. For slightly super-Eddington accretion of the CBDs, Mg  ii  line appears with decreases of UV deficit, and for intermediate super-Eddington Balmer lines appear, but C iv  line never unless CBD accretion rates are extremely high. Moreover, if the CBDs are misaligned with the binary plane, it is then expected to have optical periodical variations with about ten times radio periods. [ABSTRACT FROM AUTHOR]

The quasar 3C 273 has been observed with infrared spectroastrometry (SA) of the broad Pa α line and optical reverberation mapping (RM) of the broad H β line. SA delivers information about the angular size and structure of the Pa α broad-line region (BLR), while RM delivers information about the physical size and structure of the H β BLR. Based on the fact that the two BLRs share the mass of the supermassive black hole (SMBH) and viewing inclination, a combination of SA and velocity-resolved RM (SARM) thereby allows us to simultaneously determine the SMBH mass and geometric distance through dynamically modeling the two BLRs. We construct a suite of dynamical models with different geometric configurations and apply a Bayesian approach to obtain the parameter inferences. Overall the obtained masses and distances are insensitive to specific BLR configurations but more or less depend on parameterizations of the vertical distributions. The most probable model, chosen in light of the Bayes factor, yields an angular-size distance log (D A / Mpc) = 2.83 âˆ' 0.28 + 0.32 and an SMBH mass log (M • / M ⊙) = 9.06 âˆ' 0.27 + 0.21 , which agree with the relationships between SMBH masses and bulge properties. The BLRs have an inclination of 5 âˆ' 1 + 1 degrees, consistent with that of the large-scale jet in 3C 273. Our approach reinforces the capability of SARM analysis to measure SMBH masses and distances of active galactic nuclei and quasars even though SA and RM observations are undertaken with different emission lines and/or in different periods. [ABSTRACT FROM AUTHOR]

A puzzle in NGC 1068 is how to secularly maintain the counter-rotating disc (CRD) from 0.2 to |$7\,$| pc unambiguously detected by recent ALMA observations of molecular gas. Upon further dynamical analysis, we find that the Kelvin–Helmholtz (KH) instability (KHI) results in an unavoidable catastrophe for the disc developed at the interface between the reversely rotating parts. We demonstrate that a close binary of supermassive black holes (CB-SMBHs) provides tidal torques to prevent the disc from the KH catastrophe and are led to the conclusion that there is a CB-SMBH at the centre of NGC 1068. The binary is composed of black holes with a separation of |$0.1\,$| pc from GRAVITY/VLTI observations, a total mass of 1.3 × 107 M⊙ and a mass ratio of ∼0.3 estimated from the angular momentum (AM) budget of the global system. The KHI gives rise to a gap without cold gas at the velocity interface that overlaps with the observed gap of hot and cold dust regions. Releases of kinetic energies from the KHI of the disc are in agreement with observed emissions in radio and γ-rays. Such a binary is shrinking on a time-scale much longer than the local Hubble time via gravitational waves, however, the KHI leads to an efficient annihilation of the orbital AM and a speed-up merge of the binary, providing a new mechanism for solving the long-standing issue of 'final parsec problem'. Future observations of GRAVITY+/VLTI are expected to be able to spatially resolve the CB-SMBHs suggested in this paper. [ABSTRACT FROM AUTHOR]