1. サブミリ波 VLBI による 巨大 BH 観測 国立天文台 本間 希 樹 日本メンバー：小山友明、原哲也、秦和宏、永井洋、武士俣健、 鈴木駿策、川口則之、河野裕介、江澤元、岩下浩幸 川邊良平、小川英夫 他 国際チーム： Shep Doeleman (MIT), Thomas Krichbaum (MPIfR) 他多数

2. Simple question : Is a BH really “black hole” ? Fukue et al 1989 AGN core is most-likely a super-massive black hole. Yet, there is no confirmation of existence of event horizon If one has extremely high resolution and sensitivity, it is expected that BH-accretion disk system constitute a black hole shadow in a scale of a few R_g. Direct detection of BH shadow is an ultimate confirmation of existence of BH. (or negative results may indicate an existence of naked singularity !?)

3. Apparent size of BHs Potential targets Sgr A*M = 4 x 10^6 M_sun, D = 8 kpc θs = 10 μas M87M = 3 x 10^9 M_sun, D = 16 Mpc θs = 4 μas shadow size should be 1 ~ 5 x θs Currently-expected resolution λ= 1mm, B = 8000 km θ= λ/ B = 25 μas

4. Doeleman et al. 2008 in Nature Key to resolve BH shadow ･ 37±(16,10) Intrinsic diameter of Sgr A* ･ Non detection on the JCMT-CARMA （ 3075 km ） ARO/SMT － CARMA(600km) ARO/SMT － JCMT Non-imaging analysis (traditional UV distance plot) Fukue et al 1989 The most promising way to detect BH shadow : submm VLBI 1) shorter λ, higher resolution 2) less interstellar scattering

5. Sub-mm VLBI with ASTE ASTE will be a key station for Sgr A* observations good site & longest baselines JCMT CARMA ASTE SMTO UV coverage for Sgr A* （ red: UV with ASTE ） fringe spacing ~30μas

6. To enable VLBI with ASTE Required components 230GHz RX Local generator Down Converter Recorder Frequency Standard

7. 230G-receiver & backends Receiver : cartridge-type receiver originally developed for ATF (ALMA Test Facility) Specification Single pol. 1 x SIS Mixer (DSB) IF output of 4~8 GHz (f ~ 200-250 GHz) RX test done on 13-16 Oct 2009 T_RX ~ 70-80 K (DSB) RX testing Cartridge Test includes nearly whole system (RX, local, analog backends, sampler) See P-23, P33 for system details

8. Frequency standard H-maser Kvarz H-maser may be shipped to Chile (Jan/2010), but there are some risks (troubles in transportation, power shut-down problem etc.) An alternative OCXO 8607 (the best X ’ tal) H-maser OCXO8607 troposphere ASD comparison

9. Progress at ASTE in Jan 2010 new container (for VLBI instruments) Cabling through ground Inside of VLBI container 230 GHz RX installation

10. Progress at ASTE in Jan 2010 (II) Backends installed into VLBI container Success in signal transfer from RX to VLBI digital backends

11. Results – coming soon !? First test observations at 230GHz are planed on 1 – 5 in April 2010 stations: ASTE, SMTO, Hawaii (phase-up) mainly for testing fringes, but some scientific results may be expected !? Large international campaign will be conducted in April 2011

12. feasibility ASTE-SMTO/CARMA D~10 m, B~2 GHz Tsys ~ 200, 500 K τ~ 20 sec 1σ ~ 73 mJy 5σ ~ 365 mJy 10m in Chile will constrain acceretion disk parameters For Hawaii-Chile, phase-up will be needed ? Model flux by Fish+ (2009) 1 Jy 2 Jy

13. Constraining disk parameters RIAF disk with power-low distribution (Yuan+ 93) Parameters to fit observations spina inclinationθ PAξ amplitudeV0 Even three-station results say something about the parameters (implying θ>40 deg) Broderick+ (2009)

14. Future prospect Near-term 2010 March230 GHzSingle-pol. 4 Gbps 2011 March230 GHzSingle-pol. 4/8 Gbps probably large campaign with other wavelengths 2012 March230/345 ?Single/dual-pol. 8/16 Gbps ? Mid-term Hawaii phase-upon-going (2011?) ALMA phase-upplanned more telescopeLMT?, NZ?, SP? Target: accretion disk, BH shadow, hot spot motion and GR tests etc, jet launch etc