KaVA study of FSRQ 1928+738
Kunwoo Lee (Seoul National University)
Jongho Park (ASIAA), Sascha Trippe (SNU),
Masanori Nakamura (ASIAA)

Jets from Super Massive Black Hole
●Relativistic jet (v ~ c)●Narrow opening angle (θop <1 ∘ )●●Flat Spectrum Radio Quasar(Top View)

Synchrotron radiation- radio bright- optically thick(upstream region)

Image Credit : Sophia Dagnello, NRAO/AUI/NSF

Basic information of FSRQ 1928+738
MOJAVE 15 GHz Image

Optically thick core

Optically thin extended jet●Common Name : 4C +73.18●z ~ 0.302●

Flat Spectrum Radio Quasar●

S 43 >3 Jy●High Dec (+73)→ Ease of observation↔ Not many monitoring programs- Gamma-ray weak
- Low polarization
http://www.physics.purdue.edu/astro/MOJAVE/sourcepages/1928+738.shtml

KaVA Monitoring of FSRQ 1928+738
KaVA 43 GHz Image●

Main goal- (1) Exploring its variability- (2) its jet kinematics
for each knots (components)●

KaVA Q band 43 GHz●2017 Feb ~ 2019 Jan (~2yr)●

Monthly interval

KaVA Monitoring of FSRQ 1928+738(1) Exploring its variability → Light curve analysis(2) Jet kinematics → Proper motion analysis

KaVA Monitoring of FSRQ 1928+738

δ≡sD Lδ var =c Δ t decay (1+ z)

Jorstad et al. (05, 17)(1) Outer knots are more beemed (boosted)(2) Inner knots have longer timescale

1γ(1−β cosθ)S obs = S intr ×δ3−αΔ t obs =Δ t intr /δKaVA Monitoring of FSRQ 1928+738
KaVA 43 GHz light curve●

Flare : exponential rise/decay●2 flares in the light curve- 1 flare / year

●Peak of the flares: maintenance seasons of KVN

Light curve analysis of FSRQ 1928+738●

SMA 225GHz / (OVRO & MOJAVE 15GHz) light curves- Global trend of exponential decay: Residuals are notable 2017 - 2019http://sma1.sma.hawaii.edu/callist/callist.html?plot=1927%2B739
http://www.astro.caltech.edu/ovroblazars/data.php?page=data_return&source=J1927+7358

Light curve analysis of FSRQ 1928+738●

Correlated flares- SMA 225GHz / KaVA 43GHz- 2 distinct flares are notable- No time lag Δ t∼0●

OVRO / MOJAVE 15GHz- 2 flares are not notable- no obvious correlations●Correlation with 1st / 2nd flare ?
(KaVA 43GHz)

Light curve analysis of FSRQ 1928+738●

SMA 225GHz / OVRO 15GHz, global trend looks similar: year-scale time lags are foundLight curve analysis of FSRQ 1928+738●

Assuming no time lag(225 - 43GHz pair)●

Adopting previous time lag(43 - 15 GHz pair)~ (225 - 15 GHz pair): ~1yr●MOJAVE – KaVA
: similar light curve~yr shiftLight curve analysis of FSRQ 1928+738●●

Extremely long Time lag(yr-scale)Origin of time-lag: locational difference→ light travel time

●Origin : Doppler boostingΔ t obs =Δ t intr /δ
●FSRQ 1633+382 (Algaba+2018)
Δ t lag=30±30 daysδ∼20~yr shiftJet Kinematics of FSRQ 1928+738●

Jet kinematics: βappincreases

as a function of distanceβapp =β cos θ(1−β cos θ)●Real acceleration?
or projection effect?

Jet Kinematics of FSRQ 1928+738
22β +δ +1
Γ= app2δ

●Jet kinematics: βapp & δ increase
as a function of distanceβapp =β cos θ(1−β cos θ)●Γ increases
as a function of distance: Real Acceleration!!

Jet Kinematics of FSRQ 1928+738●

Jet kinematics (cross-checking): Both data shows acceleration●

What about collimation?

Jet Kinematics of FSRQ 1928+738
W ( z)∝ zaa~0.6●

Jet kinematics: Both data shows acceleration●

Jet collimation W ( z )∝ z a , a∼0.6: parabolic jet (being collimated)→ Acceleration & Collimation

Jet Kinematics of FSRQ 1928+738●

Jet kinematics: Both data shows acceleration
at (0 ~ 6 mas region)●Acceleration & Collimation Zone

●Q1) Acceleration keep going?

●Q2) Max of βapp ?

Jet Kinematics of FSRQ 1928+738●

Jet kinematics: Acceleration & Deceleration(flattened)(0 ~ 30 mas region)

Xband & Cband images are from http://astrogeo.org/vlbi_images/

KaVA Monitoring of FSRQ 1928+738
Hada+ 2017●

Jet kinematics: Acceleration & Deceleration(flattened)●

Resembles M87 (HST-1)?

●

Transition at ~ 3×10 R s

65cf ) M87 : at ~ 5×10 R s

KaVA Monitoring of FSRQ 1928+738
Hada+ 2017

●Acceleration → Deceleration transition in jet kinematics●Parabolic → Conical transition in jet geometry●Positional Coincidence

Nakamura+ 2018

KaVA Monitoring of FSRQ 1928+738???

●Acceleration → Deceleration transition in jet kinematics●Parabolic → Conical transition is expected !!!

Thank you