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

Simple question : Is a BH really “black hole” ?

Fukue et al 1989

•AGN core is most-likely a super-massiveblack hole.

•Yet, there is no confirmation of existenceof event horizon

If one has extremely high resolution and sensitivity,it is expected that BH-accretion disk system constitute ablack 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 !?)

Apparent size of BHs• Potential targets

Sgr A* M = 4 x 10^6 M_sun, D = 8 kpcθs = 10 μas

M87 M = 3 x 10^9 M_sun, D = 16 Mpcθs = 4 μas

shadow size should be 1 ~ 5 x θs

• Currently-expected resolutionλ= 1mm, B = 8000 kmθ= λ/ B = 25 μas

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 BHshadow : submm VLBI

1) shorter λ, higher resolution 2) less interstellar scattering

Sub-mm VLBI with ASTEASTE 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

To enable VLBI with ASTE• Required components

230GHz RX

Local generator

Down Converter

Recorder

Frequency Standard

230G-receiver & backends

• Receiver : cartridge-type receiver originally developed for ATF (ALMA Test Facility)

• SpecificationSingle pol.1 x SIS Mixer (DSB) IF output of 4~8 GHz (f ~ 200-250 GHz)

• RX test done on 13-16Oct 2009T_RX ~ 70-80 K (DSB)

RX testingCartridge

Test includes nearly whole system (RX, local, analog backends, sampler)See P-23, P33 for system details

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 alternativeOCXO 8607(the best X’tal)

H-maser

OCXO8607

troposphere

ASD comparison

Progress at ASTE in Jan 2010

new container (for VLBI instruments)

Cabling through ground

Inside of VLBI container

230 GHz RXinstallation

Progress at ASTE in Jan 2010 (II)

Backends installedinto VLBI container

Success in signal transfer from RXto VLBI digital backends

Results – coming soon !?

• First test observations at 230GHz are planedon 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

feasibility• ASTE-SMTO/CARMA

D~10 m, B~2 GHzTsys ~ 200, 500 Kτ~ 20 sec

1σ ~ 73 mJy5σ ~ 365 mJy

10m in Chile willconstrain acceretion disk parameters

For Hawaii-Chile, phase-upwill be needed ? Model flux by Fish+ (2009)

1 Jy

2 Jy

Constraining disk parameters

• RIAF disk with power-low distribution (Yuan+ 93)

• Parameters to fit observations

spin a

inclination θ

PA ξ

amplitude V0

Even three-station results

say something about the

parameters (implying θ>40 deg) Broderick+ (2009)

Future prospectNear-term

2010 March 230 GHz Single-pol. 4 Gbps2011 March 230 GHz Single-pol. 4/8 Gbps

probably large campaign with other wavelengths2012 March 230/345 ? Single/dual-pol. 8/16 Gbps ?

Mid-termHawaii phase-up on-going (2011?)ALMA phase-up plannedmore telescope LMT?, NZ?, SP?

Target: accretion disk, BH shadow, hot spot motion and GR tests etc, jet launch etc