Summary of
KaVA/EAVN observations of
M87 and Sgr A* in 2014-2018

M. Kino (NAOJ/KUTE) & BW Sohn (KASI)
on behalf of EAVN AGN Science WG
2019/Sep

EAVN Workshop 2019 Sep, at Ibaraki Univ

Grand challenge #1:
solving jet formation mechanism(c) EAVN Collaboration(c) EHT C

EHT talks
G. Bower (ASIAA)
F. Tazaki (NAOJ)

To test B-driven jet model,
we measure/constrain basic quantities of

1. velocity ﬁeld
2. B-ﬁeld
3. ﬂow geometry
BZ process at work?

EAVN Workshop 2019

v-ﬁeld, B-ﬁeld, and ﬂow geometry of M87
Park+ 2019 submitted
Ro et al. in prep
Cui et al. in prep

Longstanding problem:“Is the M87 jet fast or slow in the collimation zone?”
Asada+ (2014)

fast or slow?

Key to resolve the problem ishigh cadence monitoring,which can avoid misidentiﬁcationsof the multiple jet components!

Park+ submitted

The KaVA high-cadence (bi-weekly) monitoring in2016 reveals the proﬁle of M87’s jet velocity ﬁeld.
22GHz43GHz

Park+ submitted

1. Velocity stratiﬁcation!
2. Discrepancy btw. observation and GRMHD?!

Ro+ in prep

Constraining B-ﬁeld in M87 at 22/43GHz(2015-2016 data)

H. Ro will present new constraints on B-ﬁeldproperties via radial proﬁle of the spectral index.
Stay tuned!

Flow geometryat the jet basewhich direction?
jet opening angle?

l Unfortunately, EHT could not detect
the jet emission in EHT 2017.

EHTC+ 2019, ApJL

EHTC’s estimate of Position Angle (PA) of Forward Jet (FJ)
via matching GRMHD snapshot to the photon ring

Cui+ in prep

EAVN measure the real jet PA in 2017 AprilNormilnr
thebSouthern limb

Cui+ in prep

Position Angle [degree]

From the EAVN data, we ﬁnd that (1) wide jet-opening angle, and(2) EHTC estimates of PA_FJ reasonably agree with EAVN jet.
320

Northern limb

Southern limb
230

Relative RA[mas]EAVN Workshop 2019

Probing real vicinity of SMBH
Cho+ in prep(Zhao+ in prep)

Grand challenge #2:
Unveiling accretion ﬂow onto SMBH
Sgr A*(EAVN)

minispiral atGal. Center(VLA)

100 RsWe are almost there.
However, there is
one serious issue.

1pcVLA image(c) LoLong standing problem:“Observed radio images of Sgr A* isdominated by interstellar scattering.
So, an inference of Sgr A* image is sensitive
to an assumed scattering model.”angularbroadening

non-Gaussian &substructure(c) Akiyama

Johnson+ 2018

KaVA 7mm data (2014 Nov) shows non-Gaussianand it signiﬁcantly constrains scattering kernel.

Johnson+ 2018

The scattering parameters (α and r_in)
are ﬁnally constrained very tightly!

So, using these parameters in Johnson+2018 we can remove the eﬀect of thescattering and thus we can deriveintrinsic size of Sgr A* in 2017.

Cho+ in prep

EAVN observation of Sgr A*
on 2017 April 3rd @ 22GHz

Cho+ in prep

Intrinsic size of Sgr A*!

From this, we can potentially constrain on geometryof Sgr A* and electron distribution in it.

EAVN workshop 2019

The array is in a transition phasefrom KaVA to EAVN.
(i) Transverse motion of the M87 jet(ii) Origin of ﬂares in Sgr A*

Time allocated for initial phase ofEAVN LP in 2019 Sep – 2020 JanIlje CHO and Guangyao ZHAO

Hyunwook RO

EAVN LP of investigating
the transverse motion in M87
Declination [mas]Ro+ in prep

RA [mas]The timescale of a possible oscillation is one year scale.
Hence, long term monitoring at 22 GHz is essential to characterize its
properties. We can study on instabilities in the jet.

Do et al. (2019)

frequency distribuXon

Signiﬁcant IR ﬂare activity in 2019

observed ﬂare ﬂux (mJy)The elevated IR ﬂare activity encourages
EAVN LP monitoring of Sgr A*.
Do et al. (2019) saysl “The distribution of ﬂux variations observed thisyear is signiﬁcantly diﬀerent than the historicaldistribution.”l “Potential physical origins of Sgr A*’s
unprecedented brightness may be from changes
in the accretion-ﬂow as a result of the star S0-2‘sclosest passage to the black hole in 2018 or from adelayed reaction to the approach of the dusty
object G2 in 2014.”

Summary of EAVN
AGN Science WG activitiesl Paper drafting w/ KaVA Large Program data in 2014-2018
ü Park+ 2019 submitted (M87 velocity ﬁeld in 2016)
ü Ro+ in prep (M87 magnetic ﬁeld in 204-2016)
ü Cui+ in prep (M87 jet PA in 2017-2018)
ü Cho+ in prep (Sgr A* intrinsic size in 2017 April)ü Zhao+ in prep (Sgr A* intrinsic size in 2013-2016)l Conducting initial phase EAVN LP in 2019B
ü Transverse oscillation of the M87 jetü Origin of signiﬁcant ﬂares in Sgr A*l Development/upgrade of EAVNü KaVA/EAVN polarimetry (BW Sohn+, K. Hada+, J. Park)ü KaVA/EAVN phase-ref (J. Oh+)ü EATING VLBI (M. Giroletti+)
ü EAVN-high (K. Asada+)