Search for Binary Black Holes in Galactic Nuclei Hiroshi SUDOU (Gifu Univ., Japan) EAVN Workshop, Seoul, 2009 March 19

Outline  Introduction to Binary (supermassive) Black Hole (BBH)  Possible evidence for BBHs  Ideas for KVN/EAVN observations  Prospects for VSOP-2

Begelman et al Evolution Dynamical Friction Gravitational Wave Basic scenario: 1) a galaxy have a SMBH 2) galaxy merging often occurs 3) merged galaxy should have two SMBH in its center 4) two BH forms BBH system 5) they finally merge into one with gravitation wave burst

Good Target for VLBI  Lifetime of BBH can be the longest between DF phase and GW phase  The most observable examples of BBHs will have Separation ～ pc ( Mpc) Orbital period ～ 1 – 100 yr

Schematic View of BBH NLR BLR Accretion Disk Jet Torus BH 10pc 0.1pc pc Detection of orbital motion of BH is direct evidence for BBH !

Possible Evidence (1) Periodic Flux Variations OJ287 (Sillanpaa et al. 1998)

Possible Evidence(2) Jet shape Roos et al Owen et al Yokosawa and Inoue 1985 Twin jet (3C75) Precession jet ( )

Possible Evidence (3) Double AGN core Komossa et al. 2003Mines et al r ~ 1 kpc r ~ 10 pc Chandra VLBA

Detecting BBH with VLBI r [pc]P [yr]PhenonemaDetection Methodsfacility < 0.001<1Gravitational wave Pulsar timingSKA ? 0.011Double coreHigh spatial resolution imaging VSOP Core motionVLBI astrometryVERA/VLBA Periodic flareFlux monitoringKVN >1>1000Wiggling jetSensitive imagingEAVN/VLBA Combination of these methods is very important

Periodic flare due to BBH  How to find characteristic variation due to BBH ? What is variation mechanism ?  Theoretical study / simulations Hayasaki et al Multi-frequency observations are important

Flux monitoring with KVN  Searching for periodic variation with period of < a few yr  KVN is suitable for this project sensitive mm-wave (less jet contamination) multi-frequency ( GHz)  Combination with other wavelength Note: X-ray all-sky monitoring facility MAXI will be on board ISS in 2009 Based on monitoring results, we can go to further BBH search

Problems of this idea  Clarify importance of multi radio-frequency What is flaring mechanism at mm-wavelength ? More theoretical study must be needed  Source selection criteria (merging or merged galaxy ? Sensitivity limited ?)  Probability to detect orbiting BHs GW emitting phase would be very short (< 10 4 yr) compared with AGN timescale (10 8 yr ?)  More detailed discussion needed

BBH is important target for VSOP-2 Longest baseline: 25,000 km Frequency: 8, 22, and 43 GHz Spatial resolution: 40 43G Launch: FY2012 High spatial resolution is essential, 40 micro-as  Mpc for detecting harder BBHs emitting gravitation wave!

Summary  BBHs with r~0.1pc, P~10 yr would be most observable examples  Proposing idea of flux monitoring with KVN, but needed more discussion  Based on monitoring results, VSOP-2 could confirm the presence of BBH emitting gravitation wave Hoping to much friendly collaborate with East-Asia people !

Possible evidence (x) Core motion α δ GHz 50 micoro-as Radio Galaxy 3C66B Further observations are needed !

MAXI  Monitor of all-sky X-ray image  0.5 – 30 keV  Position accuracy ~ 6 arcmin  Every 90 min (1 orbit), all-sky image will be obtained  1000 X-ray source is expected to be detected, including AGN, X-ray binary, etc

Orbital period The most observable examples of BBHs will have P ～ yr

Comparison between Binary Pulsar and BBH Binary PulsarBBH ObjectNutron StarSMBH Mass1 Msolar10^8 Msolar Separation10^11cm10^17 cm Period3days50yrs GW frequencykHzmHz