Science cases with mmVLBI	
Kazuhiro Hada (NAOJ)
In the last few years, we (EA) have produced a numberof mmVLBI-related scientific results particularly on M87
Here I will overview mostly these EA-led M87 works– would help to consider our future scientific strategy or
initiative in this field	

mmVLBI: motivations so simple	
The pursuit of higher angular resolution &transparency toward AGN cores 	✓ = 34✓1mm◆✓D6000km◆ 1(µas)↵⌫syn / ne B (p+2)/2 ⌫ (p+4)/2• Resolve and image ablack hole shadow• Direct test of GR, BH spin• Physics of accretion flow,
jet launch	

Takahashi, R	

mm/submm telescopes	
GLT	

VLBA	
GBT	

CARMA	
SMT	

VLBA
SMA
JCMT
CSO	

Metsahovi	Effelsberg	 Onsala	
PdBI	
IRAM	

KVN	
Nobeyama	

LMT	

ALMA
ASTE
APEX	

ATCA
Mopra	SPT	

3mm (86GHz)	

3mm (86GHz) & 1.3mm (230GHz)	

Targets	
NASA	

NRAO	

Object	MBH(108 Msun)	

D(Mpc)	

2Rs(µas)	

SgrA*	
M87	(NGC1277)	
Sombrero	
M84	
Cen A	

0.04	
60	
170	
10	
8.5	
0.5	

0.008	
16.7	
73	
9.0	
17	3.8	20	
14	9	4.5	
2	0.5	3C84	BL Lac	3.4	
2.0	68	270	

0.2	0.03	

SgrA*	

3.7Rs	• The best laboratory
37µas	
for probing black
Doeleman+2008	
hole accretion– 3.7Rs emitting size	
From Doeleman’s slide in EHT2014 meeting	Broderick+2011	

• Detection ofhighly polarized(P~70%) signals
on HawaiiCARMA baselines• Presence ofordered B fields
on horizon scales	

M87	• 40µas (~6Rs) size core@1.3mm• 1.3mm intra-US closure phases
consistent with zero– jet-base emission is symmetric on~6Rs scale

Akiyama+2015

Adding LMT or ALMAbaselines will allow todisentangle a zoo oflaunch emission models
And…

From Akimama-san’s slide in EAVN meeting	epSVHE −2 −112(10− ph cm s )

1.0ov

1201
anarJ 55981)
M
N (MJD
S 24
M2012 Febay

Jul2201
r May Jul Sep Nov
Jan 27
Ma(MJD
Nov AprSep 201256044)

VERA 43GHz	

0.80.6800

6000.2(10− ph cm s )

400

0.0

SHE −2 −18

MilliARC SEC

0.4-0.2-0.4

Resolving TeV sitenear BH?	

200

230GHz VLBI in the middle of TeV flare	-0.6-0.8

12−2 −1(10− ph cm s )S230 (Jy)(10− ph cm s )S43 (Jy)
SVHE

S230 (Jy) S22 (Jy) SHE
8−2 −1SSpectrai
43 (Jy) index
S5 (Jy)S22 (Jy) S5 (Jy)rai index

After TeV	

Before TeV	

-1.0
1.0

0.50.0MilliARC SEC

Sep

Nov

-0.5

1201
Jan Mar-1.0

MayJul

0.5

Sep

Nov

2201
Jan Mar

0.0
MilliARC SEC

May-0.5

Jul

-1.00

Sep N o v

TeV/VERITAS

Flux increase inextended structure	

GeV/Fermi

No variability in
5.5Rs structure	

230GHz/SMA

VERA
43GHz core

VERA
22GHz core

Akiyama+2015	？	
20Rs < RTeV < 60Rs	Hada+2014	(EHT)	

(VERA)	

Magnetization degree (Ue/UB):
Testing the B-driven jet paradigm
Kino et al. 2015		

UB>>Uparticle	
(Size ~ 21µas)	

40 µas (6Rs)	

A highly B-dominated substrcuture (~20µas) isrequired to exist within the 40µas structureConstraining accretion flow via mm-polarimetry	
• |RM| observed in 230GHz
band constrained amaximum mass accretion
rate onto BH:

SMA 230GHz pol image(Kuo et al. 2014)	
SMA core|RM| < 7.5 ⇥ 10 5 rad m 2Ṁr=21Rs < 0.0074ṀrBondiADIOS• Mm-VLBI polarimetry mayallow to obtain a spatial
gradient of Mdot(r) profile
CDAF86GHz high-sensitivity VLBI imaging	
0.01pc10RsM87
VLBA+GBTDR >1500

86GHz polarization map(SNR~5)• a	Hada et al.

Ongoing mmVLBI-related activities in EA	
• 1.3mm EHT data analysis– Akiyama-san, Asada-san• 3mm GMVA/VLBA data for M87&more– Asada-san, Koyama-san, Hada

• Theoretical ground (analytical + simulation)– Kino-san, ASIAA (Nakamura-san, Pu-san)• Sparse modeling– Honma-san, Kuramochi-san, Tazaki-san• Synergetic monitor with VERA/KaVA– Kino-san, Niinuma-san, Hada

• KVN mm multi-freq. phase-ref– Jung-san• JCMT, GLT, SPART/Nobeyama•– Asada-san, Fujisawa-san, Saitoh-san, Miyoshi-san
We have our ownBalloon– Doi-san data, theory, technique, technology, telescopes, & brains!

Summary:
Why don’t we boost/accelerate our(allEA) collaboration? Now the best timing	• A number of scientific/technical developments in EA• Soon: open-sky use of APP (ALMA for VLBI) atband-3/6(?) will be available in the next year(Cycle-4)• To take initiative, we need powerful science cases
and ability to achieve them
• Focus on M87? Also SgrA* or other sources(blazars/nearby RGs)? Which band?