Imaging Compact Supermassive Binary Black Holes with VLBI G. B. Taylor (UNM), C. Rodriguez (UNM), R. T. Zavala (USNO) A. B. Peck (CfA), L. K. Pollack (UCSC), H.L. Maness (UCB), and R. W. Romani (Stanford) Black Holes: From Stars to Galaxies IAU General Assembly Prague, Aug 24, 2006

Introduction 3C 75 NGC kpc separation 1.4 kpc separation 7 kpc separation 1.4 kpc separation VLA image of 3C 75 at 6 cm (Owen et al. 1985) Chandra image of NGC 6240 (Komossa et al. 2003)

Hydra A 10 kpc

pc

C1 C at 5 GHz (Pollack et al. 2004) at 5 GHz (Pollack et al. 2004) Discovery of by Pollack et al. (2004). Possible explanations for its properties: Background Source Gravitational Lensing Jet Component Binary Supermassive Black Hole System pc

VLBA observations were made in 2005 at 0.3, 5, 8, 15, 22, and 43 GHz. We also obtained fully-calibrated 5 GHz VLBI data taken in 1990 (Xu et al. 1995), in 1996 (VCS; Beasley et al. 2002), in three epochs (1994, 1996, and 1999) of the CJ Proper Motion Survey (Britzen et al. 2003) and in 2003 (Maness et al. 2004). The Very Long Baseline Array (VLBA). The Very Long Baseline Array (VLBA).

Results Radio Continuum Rodriguez et al. astro-ph/ Naturally weighted 2005 VLBA images of at 0.3, 5, 8, 15, 22, and 43 GHz. C1: ± pc C2: ± pc Projected separation between C1 and C2 equal to 7.3 pc Evidence against background source

Component Motions Components model for the VLBA observations of Components model for the VLBA observations of Northern jet is moving away from the two central components to the northeast, N1: (0.185 ± 0.008)c N1: (0.185 ± 0.008)c N2: (0.114 ± 0.019)c N2: (0.114 ± 0.019)c Southern jet is moving away to the southwest, though more slowly, S2: ( ± )c S2: ( ± )c S3: (0.056 ± 0.010)c S3: (0.056 ± 0.010)c The results obtained for C2 show no significant motion. A limit of less than 0.088c was obtained. Evidence against jet component

Component Variability Light curves of the different components of at 5 GHz. Light curves of the different components of at 5 GHz. Component C1 substantially increases in flux density over the 15 y baseline. Component C2 is also variable. For the southern and northern components, there is no substantial variation in the flux densities over the 15 y baseline. Evidence against lensing

In both hotspots of the source, N2 and S2, a steep spectrum was found. For both central components, C1 and C2, the spectrum peaks at ~10 GHz. For both central components, C1 and C2, the spectrum peaks at ~10 GHz. Spectral index distribution between 8 and 22 GHz from the 2005 VLBA observations. Radio Continuum Spectra Evidence against lensing Evidence against jet component

HET Spectroscopy The optical spectrum at 5.6 Å spectral resolution taken by the HET Hobby-Eberly Telescope Red shoulder found suggesting two components with velocity separation of 300 km s −1. Spectrum of the core of obtained on 2004 December 11 with the 9.2m Hobby-Eberly telescope (HET).

neutral hydrogen in absorption Maness et al 2004 Evidence for Multiple velocity systems Consistent with a merger

Binary Supermassive Black Hole System Most likely explanation:

Constraints on the Mass of the Black Holes Supermassive Binary Black Hole Orbital Parameters Combining HET and VLBA observations a system mass of 1.5 × 10 8 M Sun was obtained. According to Kepler’s Laws the period of rotation for such a binary system should be ~ 1.5 × 10 5 y, implying a projected velocity between both components of ~ 0.001c. Gravitational Wave Signal Natural gravitational wave frequency (Hughes 2003) is approximately 2 × 10 −13 Hz. A binary black hole on a circular orbitin the final stage of evolution will merge within the time (Peters 1964): A binary black hole on a circular orbit in the final stage of evolution will merge within the time (Peters 1964): Merger time equal to ~10 18 y. Some other loss of angular momentum will be necessary if this system is to merge in less than a Hubble time.

VLBI Imaging of Active Galactic Nuclei VLBA Imaging Polarimetry Survey (VIPS) 1127 sources: S > 85 mJy, 65 > dec > 20, |b|>10 at 5 GHz in SDSS northern cap First epoch observations on the VLBA in 2006 Identifications and redshifts from SLOAN, HET, Palomar, … Goals: - Characterize GLAST sources - Study Evolution of Radio Sources - Study AGN environments - Find more supermassive binary black holes

Some Candidate SBBH Systems from VIPS

Conclusions C1 and C2: two active nuclei of a single galaxy. C1 and C2: two active nuclei of a single galaxy. Closest binary black hole system yet discovered. Projected separation of 7.3 pc. Closest binary black hole system yet discovered. Projected separation of 7.3 pc. Total mass of the system: 1.5 × 10 8 M Sun. Total mass of the system: 1.5 × 10 8 M Sun. Gravitational radiation frequency: 2 × 10 −13 Hz. Gravitational radiation frequency: 2 × 10 −13 Hz. Searching for more binary black hole systems. The VLBA Imaging and Polarization Survey (VIPS, Taylor et al. 2005) has imaged 1127 sources. Searching for more binary black hole systems. The VLBA Imaging and Polarization Survey (VIPS, Taylor et al. 2005) has imaged 1127 sources.