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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” ?
•AGN core is most-likely a super-massive
black hole.
•Yet, there is no confirmation of existence
of event horizon
Fukue et al 1989
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 !?)
Apparent size of BHs
• Potential targets
Sgr A* M = 4 x 10^6 M_sun, D = 8 kpc
θs = 10 μas
M87
M = 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
Key to resolve BH shadow
The most promising way to detect BH
shadow : submm VLBI
1) shorter λ, higher resolution
2) less interstellar scattering
Fukue et al 1989
ARO/SMT－CARMA(600km)
ARO/SMT－JCMT
Doeleman et al.
2008 in Nature
Non-imaging analysis (traditional UV distance plot)
･ 37±(16,10) Intrinsic diameter of Sgr A*
･ Non detection on the JCMT-CARMA（3075 km）
Sub-mm VLBI with ASTE
ASTE will be a key station for Sgr A* observations
good site & longest baselines
CARMA
SMTO
JCMT
ASTE
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)
• 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)
Cartridge
RX testing
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.)
troposphere
OCXO8607
• An alternative
OCXO 8607
(the best X’tal)
H-maser
ASD comparison
Progress at ASTE in Jan 2010
new container (for VLBI instruments)
Inside of VLBI container
230 GHz RX
installation
Cabling through ground
Progress at ASTE in Jan 2010 (II)
Backends installed
into VLBI container
Success in signal transfer from RX
to VLBI digital backends
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
feasibility
• ASTE-SMTO/CARMA
D~10 m, B~2 GHz
Tsys ~ 200, 500 K
τ~ 20 sec
2 Jy
1σ ~ 73 mJy
5σ ~ 365 mJy
1 Jy
10m in Chile will
constrain acceretion
disk parameters
For Hawaii-Chile, phase-up
will be needed ?
Model flux by Fish+ (2009)
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 prospect
Near-term
2010 March
230 GHz
Single-pol. 4 Gbps
2011 March
230 GHz
Single-pol. 4/8 Gbps
probably large campaign with other wavelengths
2012 March
230/345 ?
Single/dual-pol. 8/16 Gbps ?
Mid-term
Hawaii phase-up
ALMA phase-up
more telescope
on-going (2011?)
planned
LMT?, NZ?, SP?
Target: accretion disk, BH shadow, hot spot motion and GR tests
etc, jet launch etc

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