Outline

The quasar:

- scintillation data (3.6, 6, 13, 21, 92cm)

- timedelay experiments

- structure and intrinsic properties

- transient compact features (6cm, 21cm)

The screen

- transverse velocity

- transverse size constraints

- distance

Ger de Bruyn 1,2 & JP Macquart 2,3

1) ASTRON - Dwingeloo 2) Kapteyn Institute - Groningen3) NRAO - Socorro

SINS workshop , Socorro, May ‘06

J1819+3845: a peculiar quasar behind a fast-moving very local screen

Other collaborators on parts of the project: Jane Dennett-Thorpe, Barney Rickett, Denise Gabuzda, Leonid Gurvits, Brian Moloney

J1819+3845 & WSRT : a 7 year relationship (~1000 hrs observing)

• The first three years Dennett-Thorpe & de Bruyn (‘00,’01,’03)

- time delay, anisotropy - screen distance, velocity

- angular size, Tb and basic quasar core-jet structure

• The next four years Macquart & de Bruyn (’05,’06) de Bruyn & Macquart (in prep), others ...

- spectrum and long term source evolution (3.6, 6, 13cm) - 21cm diffractive scintillation - differential polarization imaging - unexpected recent 6cm developments - VLBI imaging

J1819+3845: a ~21m quasar at z=0.55 peaking at 30-40 GHz

Peaking around 40-50 GHz in 1999!

Variability through the seasons (1999/2002):

a sample of early lightcurves

scintillation timescale during the year(s) (>factor 10 range !)

Blue dotted line assumes Vscreen= 0 km/s

(NB: ecliptic latitude ~ 62o

hence’uniformly’ sensitive to transverse motion)

Red line

Vscreen ~ 30 km/s

STILL VERY POOR FIT in slow season !

….but excellent fit with anisotropic scintels (14:1) in PA ~ 85o

~Nov 20

The ‘effective’ transverse velocity is very small and parallel to scintles around Nov 15-25 !

This ‘stationarity’ is indeed observed in runs on 17-Nov-02 and 13-Nov-04 !!

Simultaneous split-array (5+4+5 telescopes) observations

2.3, 4.9 and 8.5 GHz

Variable timedelay of ~ 100 seconds proof of scintillation !

Dennett-Thorpe & de Bruyn, 2002

7 Jan 2001

However, the velocity solution is degenerate in (VRA,VDec) for very anisotropic turbulence

1 February

The ‘preferred’ velocity solution implies Jan-March motion perpendicular to the very elongated scintels (~100,000 x 1000,000 km)

Barney Rickett, (priv comm)

Summary of Tb – size and distance – CN2 dependencies

Best estimate: distance ~ 4-12 pc Angular size 100-300 arcsec Tb~ 1011.5-12 K

DennettThorpe & deBruyn, 2003

Summary of 7 years of monitoring : a slowly evolving AGN outburst

All short-term variations probably due to scintillation: i.e. external

except 1-April-02 !?

3 highest 6cm peaks in 7 years all within 12h !

New extremely fast variations appear in 2004 and 2005.

They appear to come and go on ~ 1-2 month timescales. Probably intrinsic

Power spectra at 6cm in Feb 00, 03, 04, 05

Note the appearance of extra peaks at log (rad/s) ~ 10-2 and 10-2.3

Interpretation/analysis based on:

- core-jet structure of radio source

- opaque synchrotron selfabsorbed core at 6cm /5 GHz (at least till 2006)

- highly polarized features, slowly changing, in jet

- time delay varies with season: T (I - Q/U) is always +ve (from >4h - 0.9h)

Interesting from AGN physics point of view BUT

- realization that this made possible a ‘direct’ distance measurement of the scattering screen

from VLBI-size + (I - Q/U) time delay !

(work in progress with Denise Gabuzda, Brian Moloney and Leonid Gurvits)

Polarization monitoring at 6cm: allowing differential I-Q/U/V imaging at the ~10 arcsec level !!

The ‘polarization fun’ really started in summer 2002

~ 5 mJy polarized flux

I

Q

U

V

Beautiful series of I,Q,U,V variations in winter/spring 05/06

I - Q/U time delay varies still smoothly from >4h to ~ 55m

In spring 2006 there appears only one single dominant Q and U feature

22 Jan 2006

Frozen screen turbulence on >>hours timescale

6cm temporal asymmetries and consistent 3.6-6cm delay --> core-jet with SSA-opacity effects influencing centroid position

time-delay between 8.4 GHz and 5 GHz ‘centroids’ is about 20m in the spring season

8 GHz VLBI image 4-Jun-03

N-S displacement I - Q/U

about 600 arcsec at 8.4 GHz

Gabuzda, Moloney etal, in prep

VLBI separation at 8.4 GHz

~ 600 arcsec

Q 5 GHz (& 8.4 GHz ?)

U 5 GHz (& 8.4 GHz ?)

I 5 GHz

I 8.4 GHz

Deriving the distance of the scattering screen to J1819+3845

T 55m

T 20m

= (55m+20m) x 30 km/s = 1.4 1010 cm / Dscreen = 600 / 2.06 1011

Dscreen 4.9 1018 cm = 1.6 1 pc !!

A final useful constraint on the screen properties comes from (a dozen) widefield WSRT 21cm observations

200 sources S21cm > 100 Jy

Several ‘flat’ spectrum sources (quasars) with fluxdensities of about 1-20 mJy within 0.5o of J1819+3845

Because S = 2kTb 2 / 2

(S /Tb)0.5

All things being equal: faint sources should show stronger scintillations !!

However, they only show weak (m < 5%) ‘flux flickering’ at 6/21cm.

transverse screen size probably less than 0.5o

1.25o x 1.25o field

to be continued

1) VLBI-size angular size + (I - Q/U) time delay

(& 10m timescale Fresnel scale at 6cm ?)

2) Scintillation timedelay and seasonal variations

3) Scintillation seen for 7 years in which screen moved 7 years x 35 km/s

4) Surrounding compact sources within 0.5o show little or no scintillations

Derived properties of the screen:

distance ~ 2 pc (~ 1019 cm)

Vtransverse relative to Sun ~ 35 km/s

transverse dimensions > 1015 cm

transverse dimensions < 1017 cm (0.01 x 1019 cm)

Distance from ~ 20-30 pc to 4-12 pc to ~ 2 pc

Edge of Local Bubble ? Vega (Lyrae) ? edge LIC, Mic clouds ?

Bhat et al (1998) d=8.4 pc, 3o away Linsky (SINS, yesterday)

Line of sight to J1819+3845 crosses the edge of the local bubble at about 30 pc distance

Bhat et al 1998

J1819+3845 and its ‘screen’

Concluding: we are finally closing in (after 7 years !)

Screen properties

• distance ~ 2 pc • 1015 cm < Dtransverse < 1017 cm• ‘thin’ ? (anisotropic turbulence)• Vtrans ~ 35 km/s • associated with ??• density, temperature, pressure ??

• (excess RM <50 rad/m2)

AGN properties

• Core-jet 50 - 500 arcsec (0.2 - 2 pc)• Non-moving/expanding nozzle ? • Tb 1012 K , i.e. NOT very ‘hot’ • Complex polarized jet, not moving ? • Transient compact components in 2004/05 (located where ?)• Very compact features also at 21cm (DISS)

• Unusual source: no extended structure, young ??