Supermassive Binary Black Hole System Research Articles

Upper Bounds on the Low‐Frequency Stochastic Gravitational Wave Background from Pulsar Timing Observations: Current Limits and Future Prospects

Using a statistically rigorous analysis method, we place limits on the existence of an isotropic stochastic gravitational wave background using pulsar timing observations. We consider backgrounds whose characteristic strain spectra may be described as a power-law dependence with frequency. Such backgrounds include an astrophysical background produced by coalescing supermassive black-hole binary systems and cosmological backgrounds due to relic gravitational waves and cosmic strings. Using the best available data, we obtain an upper limit on the energy density per unit logarithmic frequency interval of \Omega^{\rm SMBH}_g(1/8yr) h^2 <= 1.9 x 10^{-8} for an astrophysical background which is five times more stringent than the earlier Kaspi et al. (1994) limit of 1.1 x 10^{-7}. We also provide limits on a background due to relic gravitational waves and cosmic strings of \Omega^{\rm relic}_g(1/8yr) h^2 <= 2.0 x 10^{-8} and \Omega^{\rm cs}_g(1/8yr) h^2 <= 1.9 x 10^{-8} respectively. All of the quoted upper limits correspond to a 0.1% false alarm rate together with a 95% detection rate. We discuss the physical implications of these results and highlight the future possibilities of the Parkes Pulsar Timing Array project. We find that our current results can 1) constrain the merger rate of supermassive binary black hole systems at high red shift, 2) rule out some relationships between the black hole mass and the galactic halo mass, 3) constrain the rate of expansion in the inflationary era and 4) provide an upper bound on the dimensionless tension of a cosmic string background.

A Compact Supermassive Binary Black Hole System

We report on the discovery of a supermassive binary black hole system in the radio galaxy 0402+379, with a projected separation between the two black holes of just 7.3 pc. This is the closest black hole pair yet found by more than 2 orders of magnitude. These results are based on recent multifrequency observations using the Very Long Baseline Array (VLBA), which reveal two compact, variable, flat-spectrum, active nuclei within the elliptical host galaxy of 0402+379. Multiepoch observations from the VLBA also provide constraints on the total mass and dynamics of the system. Low spectral resolution spectroscopy using the Hobby-Eberly Telescope indicates two velocity systems with a combined mass of the two black holes of ~1.5 × 108 M☉. The two nuclei appear stationary, while the jets emanating from the weaker of the two nuclei appear to move out and terminate in bright hot spots. The discovery of this system has implications for the number of close binary black holes that might be sources of gravitational radiation. Green Bank Telescope observations at 22 GHz to search for water masers in this interesting system are also presented.

The Linear Accelerating Superluminal Motion Model

Accelerating superluminal motions were detected recently by multiepoch very long baseline interferometry observations. Here a linear accelerating superluminal motion (LASM) model is proposed to interpret the observed phenomena. The model provides a direct and accurate way to estimate the viewing angle of a relativistic jet. It also predicts that both Doppler boosting and deboosting effects may take place in an accelerating forward jet. The LASM model is applied to the data of the quasar 3C 273, and the initial velocity, acceleration, and viewing angle of its three components are derived through model fits. The variations of the viewing angle suggest that a supermassive black hole binary system may exist in the center of 3C 273. The gap between the inner and outer jet in some radio-loud active galactic nuclei my be explained in terms of Doppler deboosting effects when the components accelerate to ultrarelativistic speed.

Constraining the Properties of Supermassive Black Hole Systems Using Pulsar Timing: Application to 3C 66B

Data from long term timing observations of the radio pulsar PSR B1855+09 have been searched for the signature of Gravitational waves (G-waves) emitted by the proposed supermassive binary black hole system in 3C66B.

Can long-term periodic variability and jet helicity in 3C 120 be explained by jet precession?

Optical variability of 3C 120 is discussed in the framework of jet precession. Specifically, we assume that the observed long-term periodic variability is produced by the emission from an underlying jet with a time-dependent boosting factor driven by precession. The differences in the apparent velocities of the different superluminal components in the milliarcsec jet can also be explained by the precession model as being related to changes in the viewing angle. The evolution of the jet components has been used to determine the parameters of the precession model, which also reproduce the helical structure seen at large scales. Among the possible mechanisms that could produce jet precession, we consider that 3C 120 harbours a supermassive black hole binary system in its nuclear region, and that torques induced by misalignment between the accretion disc and the orbital plane of the secondary black hole are responsible for this precession; we estimate upper and lower limits for the black holes masses and their mean separation.

Precession in the Inner Jet of 3C 345

VLBI observations have shown that the parsec jet of 3C 345 is formed by several components, ejected from the core with superluminal velocities and traveling along bent trajectories on the plane of the sky. We interpret the differences in velocity and position angle among the different features at formation time as the result of parsec-scale precession of the relativistic jet, and we calculate the aperture angle of the precession cone, the angle between the cone axis and the line of sight, and the Lorentz factor associated with the jet bulk motion. We assumed a precession period of 10.1 yr, which is one of the long-term B-band light-curve periods reported in the literature. We propose that boosting of the underlying jet emission, which is time-dependent as a result of precession, is responsible for this long-term optical variability. Jet precession with periods of several years can be produced in supermassive black hole binary systems, when the secondary black hole is in an orbit noncoplanar with the primary accretion disk, inducing torques in the inner parts of the disk. Assuming that this mechanism is responsible for the jet precession in 3C 345, we estimate upper and lower limits for the masses of the two black holes, as well as their mean separation. We found a correlation between the formation of jet components and the occurrence of strong optical flares, as well as a very strong anticorrelation between the intensity of these flares and the time required for the components to reach the maximum flux density at radio frequencies.

Multi-epoch VSOP observations of 1928+738

We have undertaken a series of eight VSOP observations of the relatively low-redshift ( z=0.3) core-dominated quasar 1928+738 in order to test the claims by Roos et al. [AJ 409 (1993) 130] that on the pc-scale this source shows evidence of a super-massive binary black hole system in the form of a precessing ballistic relativistic jet. We have detected a wide range of proper motions from nearly stationary (0.02 mas/yr or 0.5 c) to relatively fast (0.82 mas/yr or 19 c). We also find that the observed kinematics are more consistent with a ballistic precessing relativistic jet model than a relativistic helical jet model.