Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)

VERA and KaVA (KVN+VERA) observationsof Sgr A* in 2013

Kazunori Akiyama(U. Tokyo / NAOJ / JSPS Research Fellow)
on the behalf of KaVA AGN WG et al.

13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)

What is the Galactic Center Sgr A*

Recent Results on the Galactic Black Hole

19

Training of Data Analysis

Genzel+Fig. 15 Stellar orbits at the Galactic center proving the existence of a black hole. The starS0-2 dominates our knowledge about the central potential, since with an orbital period of 16
years it has been tracked throughout a whole orbit. The other stars have longer orbital periods
and therefore only a fraction of their orbits is covered by observations.

Akiyama et al. 2013, PASJ

- The nearest SMBH
( 8 kpc / 4 x 106 Msolar )- Largest angular size ofEver since the discovery of S0-2 and other similarly fast-moving stars at the center of the Milky
Way (Eckart & Genzel 1997; Eckart et al. 2002; Ghez et al. 1998, 2000), the prospect of using stellar
orbits to make ultra-precise measurements of the distance to the Galactic center (Ro ), and, more ambitiously, to measure post-Newtonian effects has been anticipated by many under the assumption thatradial velocities and more accurate astrometry would eventually be obtained (e.g. Jaroszynski 1998;
Rubilar & Eckart 2001; Weinberg et al. 2005; Zucker et al. 2006; Will 2008; Angélil et al. 2010; Merritt
et al. 2010).
Ro – a fundamental parameter for models of the Galaxy – affects almost all questions of Galactic
structure and mass. It can be estimated by fitting S0-2’s orbital motions with a Keplerian model (e.g.,
Ghez et al. 2008; Gillessen et al. 2009a,b), and our current best fit value for this parameter is 7.7 ±0.4 kpc, with an uncertainty that is highly correlated with the uncertainty in the mass of the black hole(see figure 16). With continued astrometric and spectroscopic monitoring, the precision in Ro should
improve by an order of magnitude. With this measurement accuracy, it would be possible to improve
estimates of the amount and distribution of dark mass in the Milky Way and to possibly recalibrate rungsof the cosmic distance ladder (e.g. Olling & Merrifield 2000; Majewski et al. 2006).
With care, the planned astrometric and spectroscopic adaptive optics observations for Ro , along withmeasurements of other short-period stars, should enable measurements of stellar orbits with sufficientprecision to detect non-Keplerian effects due to General Relativity (GR) and extended dark mass. The
leading order effects are the special relativistic transverse Doppler shift and the gravitational redshift.

the Event horizon ( 1 Rs = 0.01 mas )- The best laboratory to study
an environment around SMBH
13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)Figure 7: Three-color overlay of the position-velocity diagrams for 2008, 2011 and 2012 as shown in!"#$%&'"()*+,%-'$%.$+/"$0*'$12%34$56$,-$+/"$5*2*1+,1$7"-+"($The Gas Cloud G2

figure 6.

the G2 cloud

Head
Training of Data Analysis

Tail

Figure 9: L'-band (3.8 µm) image of the Galactic CenterFigure
obtainedwith map
NACO
at theVLT
on July
8: Br-"of G2.
The
image
was 6,
obtained from the 2012 SINFONI data set by extracting 25
2011. Note the 2.6''-long dust feature to the Southeast, roughly
along
the
direction
from
which
G2
channel maps from 2.1695 µm to 2.1815 µm in the yellow rectangle, each with a spectral smoothing
approached Sgr A*. The brighter gas streamer from the ofNortheast
the Southwest
is the so5 pixels towards
and subtracting
the spectrally
neighboring channels. In each channel map then a '-clippingEarthcalled mini-spiral.
at ' = 1.5 was applied. Finally, for each pixel the brightest value of the 25 channel maps was selected(since the gas at different positions is at different velocities), and the image was smoothed with aGaussian beam with FWHM=3 pix. The head and the tail are marked with arrows.

The Gas Cloud with 3 M
the galactic SMBH Sgr A*

is approaching to(Gillessen et al. 2012, Natrue)“Once-in-a-lifetime event” for VERA
and KaVA to have a look at thedinner of SMBH
13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)*+,%-'$%.$+/"$0*'$12%34$56$,-$+/"$5*2*1+,1$7"-+"($Sgr A* will encounter main part of the G2 cloud in 2014

Training of Data Analysis(Gillessen et al. 2013a)

e-color overlay of the position-velocity diagrams for 2008, 2011 and 2012 as shown in

13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)*+,%-'$%.$+/"$0*'$12%34$56$,-$+/"$5*2*1+,1$7"-+"($Sgr A* will encounter main part of the G2 cloud in 2014

2008

Training of Data Analysis(Gillessen et al. 2013a)

e-color overlay of the position-velocity diagrams for 2008, 2011 and 2012 as shown in

13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)*+,%-'$%.$+/"$0*'$12%34$56$,-$+/"$5*2*1+,1$7"-+"($Sgr A* will encounter main part of the G2 cloud in 2014

2011
2008

Training of Data Analysis(Gillessen et al. 2013a)

e-color overlay of the position-velocity diagrams for 2008, 2011 and 2012 as shown in

13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)*+,%-'$%.$+/"$0*'$12%34$56$,-$+/"$5*2*1+,1$7"-+"($Sgr A* will encounter main part of the G2 cloud in 2014
2012
2011
2008

Training of Data Analysis(Gillessen et al. 2013a)

e-color overlay of the position-velocity diagrams for 2008, 2011 and 2012 as shown in

13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)*+,%-'$%.$+/"$0*'$12%34$56$,-$+/"$5*2*1+,1$7"-+"($Sgr A* will encounter main part of the G2 cloud in 20142013 Apr
2012
2011
2008

Training of Data Analysis(Gillessen et al. 2013a)

e-color overlay of the position-velocity diagrams for 2008, 2011 and 2012 as shown in

13年9月28日土曜日(Gillessen et al. 2013b)

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)*+,%-'$%.$+/"$0*'$12%34$56$,-$+/"$5*2*1+,1$7"-+"($Sgr A* will encounter main part of the G2 cloud in 20142013 Apr
2012
2011
2008

Training of Data Analysis(Gillessen et al. 2013a)

e-color overlay of the position-velocity diagrams for 2008, 2011 and 2012 as shown in(Gillessen et al. 2013b)- The point of the G2 head already passed
pericenter in April 2013
(Gillessen et al. 2013b)

13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)*+,%-'$%.$+/"$0*'$12%34$56$,-$+/"$5*2*1+,1$7"-+"($Sgr A* will encounter main part of the G2 cloud in 20142013 Apr
2012
2011
2008

Training of Data Analysis(Gillessen et al. 2013a)

e-coloroverlay of the position-velocity diagrams for 2008, 2011 and 2012 as shown in
3500

3000

Phifer et al. 2013
this work, Br Γastrometry
this work, L' band astrometry- The point of the G2 head already passed
pericenter in April 2013
(Gillessen et al. 2013b)

vLSR km s

2500- Main part of the G2 cloud will arrive at
pericenter in early 2014

2000

1500

VLT
: Gillessen et al. 2013b
Keck 10m: Phifer et al. 2013

1000

2008

(Gillessen et al. 2013b)

2009

13年9月28日土曜日

2010

2011
t yr

2012

2013

2014

(Gillessen et al. 2013b)

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)

Expected phenomena related with G2 encounter
1. flare of recombination lines (in NIR)
before pericenter passage(early 2014?)
2. flare of the G2 bow shock (inradio)
Training of Data Analysis
around pericenter passage(early 2014?)

Possibly detected with VLBI
3. flare in Sgr A* (in radio, NIR, X-ray)after pericenter passage(middle/late 2014?)

Increase in its radio flux and size
Possible jet formation
13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)

Expected timeline and observations of our groups
Arrival of the head part

Arrival of the main part

Recombinationline flare (IR)G2

Ambient

G2 Bowshock

flux/size enhancement?

Sgr A*

Training of Data Analysis

2013

RIAF/Jet FlareJet formation

20141) Monitoring Project (Jan. 2013 ~ )1) VERA Monitor of the radio flux and size at 43 GHz (an interval of 3 weeks)2) Single Dish Monitor (Weekly/bi-weekly)- 1.4/2.4/8 GHz using Medicina/Noto 30 m Telescopes (Giroletti et al.)- 22/43/86 GHz in KVN (Sohn, Lee et al.)2) Baseline measurements with KaVA (VERA + KVN) at 22/43 GHz
Quasi-simultaneous observations with EHT 230 GHz (Doeleman et al.)and GMVA 86 GHz (Trippe et al.) in March/May 2013

3) ToO observations: astrometric observations with KaVA at 22/43 GHz
13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)Further collaborations
Subaru ToO Proposal(Accepted in 2013B, submitted for 2014A; Nishiyama et al.)- SUBARU+VERA collaboration to trace possible jet formation in Sgr A*
The XVP Projects (International MWL collaborations)- X-ray: Nustar (Barriere+), Chandra (Neilsen+), XMM (Goldwurm+),
Training of Data Analysis
Swift (Degenaar+)- γ-ray: HESS (Kosack+), Fermi (Su+)- NIR: VLT (Gillessen+, Eckart+), Keck (Ghez+), SUBARU (Nishiyama+),- Radio: EHT (Doelemann+), VLBA (Bower+), KaVA (Akiyama+), ALMA (Falcke+)and many other scientists (e.g. theoreticians)

13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)

Preliminary results of VERA Monitor at 43 GHz until Aug. 2013
Jan 29Mar 05 Mar 23

Aug 14

May 7

MaintenanceSeasonRadio flux: 8 % variation

Major: < 1 % variation Minor: 7 % variation
Training of Data Analysis

MaintenanceSeasonAlthough the head part of the G2 cloud passed pericenter before April 2013,
no obvious variations was appeared in the nucleus of Sgr A* until August 2013.
13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)

Preliminary results of VERA Monitor at 43 GHz until Aug. 2013
Freefall time scale from pericenter to Sgr A* ~ few months
some fraction of the head part of the G2 gas might arriveat Sgr A* in the middle of 2013.
Luminosity of the central engine
Accretion disk : L ∝ Mdot2 (Mahadevan 1997)
Jet case: L ∝ Mdot1.4 (Falcke et al. 1995)
Training of Data Analysis

size at mm-wavelength
Accretion disk : size ∝ Mdot
Jet case: (?)(Mahadevan 1997)

No obvious variation in mas-scale structure indicatescurrent feeding rate from the G2 cloud to the central
engine was lower than typical mass accretion rate.
13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)

Future observations with KaVA (March 2014 - )~ March 2014

UV coverage and Visibility amplitude of Sgr A*
VERA

VERA

Training of Data Analysis

VERA monitor --> KaVA Monitor- More accurate determination of the size
- Better imaging quality (for possible formation of jet and bowshock)
13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)

Future observations with KaVA (March 2014 - )UV coverage and Visibility amplitude of Sgr A*

March 2014 ~KaVA (KVN+VERA)

VERA

KVN

M
Y

U
Training of Data Analysis

T
VLBA

R
O

S

VERA monitor --> KaVA Monitor- More accurate determination of the size
- Better imaging quality (for possible formation of jet and bowshock)
13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)Our Suggestions about “open-use” KaVA observations
Considering the current status of KJCC, there has been a large risk oftaking a lot of time to correlate KaVA 1 Gbps data with KJCC.
- Difficult to reduce scientifically important data required to be published quickly(e.g. Sgr A* data) in reasonable time scale.
- Slow speeds of KJCC correlationTraining
possibly
put pressure on amounts
of Data Analysis
of available D2K tapes andMark 5B disk packs
Suggestion
Please open simultaneous recording with D1K and 1 Gbps in semesters 2014A,
2014B- A lot of KaVA data have been correlated with Mitaka FX correlator.
This would provide us the robust data delivery.
- Even in the worst case of shortages of D2K tapes and Mark 5B disk packs,
we can substitute D1K data, and release D2K and 1 Gbps data.
13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)We will continue on looking at the “dinner” of
the galactic supermassive black hole
Training of Data Analysis

13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)Training of Data Analysis

supporting slides

13年9月28日土曜日

Kazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)Flare in Sgr A*

The Astrophysical Journal Letters, 752:L1 (6pp), 2012 June 10(a)Mościbrodzka et al.

(b)

(c)

(d)

(f)

(g)

(h)

Training of Data Analysis(e)Figure 1. Horizon silhouette detectability at 230 GHz for various Ṁ. Panels (a) to (h) show images of Sgr A* calculated for Ṁ = (0.5, 1, 2, 4, 8, 16, 32, 64) Ṁ0 ,respectively. The center of the circle is positioned at the image centroid and its radius, r = (σ1 + σ2 )/2 is the rms radius of the emitting region.
(A color version of this figure is available in the online journal.)

1) increase in its luminosity (detectable in Radio, IR, X-ray)

Figures 1 and 2 show the variation of 230 and 345 GHz
Sgr A* model images with Ṁ (based on a single snapshot fromthe 3D GRMHD simulation). Evidently modest increases in Ṁmake the ring-like signature of the photon orbit easier to detect.
For Ṁ ! 8 Ṁ0 , however, the ring (or black hole silhouette) is
hidden beneath the synchrotron photosphere at 230 GHz. The
silhouette survives to higher Ṁ at 345 GHz, disappearing onlyat Ṁ ! 16 Ṁ0 . For low Ṁ, the silhouette is also difficult to
detect because the emitting region is too small.
Figure 3 shows the accretion flow image size (!σ ", circle radii
in Figures 1 and 2) and flux at 230 and 345 GHz as a functionof Ṁ. Different point types correspond to different simulation
snapshots. The size of the emission region and flux increase
with Ṁ. The 345/230 GHz flux ratio increases with increasingṀ; this is caused by the shift of the synchrotron peak towardhigher energies at higher Ṁ.
The following fitting formulas describe how σ and Fν dependon Ṁ:

Accretion disk : L ∝ Mdot2 (Mahadevan 1997)
Jet case: L ∝ Mdot1.4 (Falcke et al. 1995)
2) increase in its size at mm-wavelength
Accretion disk : size ∝ Mdot
Jet case: (?)(Mahadevan 1997)
Ṁ 0.38
15.2 × ( Ṁ) ,Ṁfor Ṁ
<23) first discovery of the jet ejection from the Sgr A*!σ "230 GHz =0Ṁ
for Ṁ
"20Ṁ 0.31Ṁ

0

13年9月28日土曜日

021.1 × log ( Ṁ ) + 13,
10 Ṁ



[µas]
(1)

Moscibrodzka
et al. 2012
F230 GHz =F345 GHz =Ṁ 1.03
3.17 × ( Ṁ) ,Ṁfor Ṁ
<2

00

10.62 × log ( Ṁ ) + 3.8,
10 ṀṀ 1.3
3.2 × ( Ṁ
) ,

0

0

Ṁ
for Ṁ
"20[Jy] (3)Ṁ
for Ṁ
<20

25.13 × log ( Ṁ ) + 0.54,
10 Ṁ
0

Ṁ
for Ṁ
"2

[Jy].

0

(4)
The constants are nontrivial to interpret because they encapsulate the complexities of the accretion flow structure and relativistic radiation transport effects. The fitting functions are shown in
Figure 3 as dashed and dotted lines.
Figure 4 shows the relation between two observables, σ andFν . The size is a linear function of the flux and increases more
steeply at 230 GHz than at 345 GHz. We also provide two
phenomenological scaling laws fitted to the data:!σ "230 GHz = 1.72(F230 GHz /Jy) + 9.3 [µas](5)!σ "345 GHz = 0.73(F345 GHz /Jy) + 9.2 [µas].

(6)

Note that these fits apply to the best-bet model only. For other a∗ ,Ti /Te , or i, the scalings will be slightly different. If the sourceis optically thick, the source size–flux relation generally traces
Te (r); in our model Te ∝ 1/r.
Equation (5) predicts a size increase of 9% in Sgr A* when

in

min

Observatory Userʼs meeting, 2013/10/03 (Wed)e. Pcl is the initial pressure of the cloud (allKazunori
but P6Akiyama,
are in Mizusawa
pressureVLBI
equilibriumwith the disk).

Expected size of the G2 Bow-shockt = 2014.25

t = 2014.6

iy/1000 RG

2014.6

Training of Data Analysis

Narayan etx/1000RGal. 2012

Sadowski et al. 2013a, 2013b

x/1000 RG

sk (model M1) corresponding to epochs t = 2013.4, 2014.25, 2014.6.Abarca,
The axesSadowski
are in units&ofSironi
1000 R
G . The2013

The size of shocked region ~ several x 103 Rsch ~ several x 10 mas

with VLBI
5.3 Position- velocity diagrams
significantly.possibly
Both of detected
n13年9月28日土曜日
see from Fig. 6, theKazunori Akiyama, Mizusawa VLBI Observatory Userʼs meeting, 2013/10/03 (Wed)Introduction: Intrinsic structure of Sgr A* at cm/mm
Sub-mm Bump in SED

λ-dependence of intrinsic size100

τ~1 at several x 100 GHz

λ1.4~1.7

10

22 GHz1(Broderick et al. 2009)+

Training of Data Analysis

43 GHz86 GHz0.1

opticallythick

230 GHz
0.01

0.1

1
Wavelength (cm)Wavelength (cm)

Flux (Jy)intrinsic
size
FWHM size(mas)(mas)(Doeleman et al. 2008)

opticallythin

10

Frequency (GHz)- Radio emission of Sgr A* comes from λ-dependent photosphere(e.g. Ozel et al 2000, Loeb & Waxman 2007, Falcke et al. 2009)- The photosphere size at 43 GHz has a variability (Bower et al. 2004)
13年9月28日土曜日