1. J1819+3845: a peculiar quasar behind a fast-moving very local screen
SINS workshop , Socorro, May ‘06
J : a peculiar quasar behind a fast-moving very local screen
Ger de Bruyn 1,2 & JP Macquart 2,3 1) ASTRON - Dwingeloo 2) Kapteyn Institute - Groningen 3) NRAO - Socorro
Other collaborators on parts of the project: Jane Dennett-Thorpe, Barney Rickett, Denise Gabuzda, Leonid Gurvits, Brian Moloney
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

2. 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

3. J1819+3845: a ~21m quasar at z=0.55 peaking at 30-40 GHz
Peaking around GHz in 1999!

4. Variability through the seasons (1999/2002):
a sample of early lightcurves

5. 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 !

6. ….but excellent fit with anisotropic scintels (14:1) in PA ~ 85o
~Nov 20

7. 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

8. Dennett-Thorpe & de Bruyn, 2002
Variable timedelay of ~ 100 seconds  proof of scintillation !
7 Jan 2001

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

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

11. Summary of Tb – size and distance – CN2 dependencies
DennettThorpe & deBruyn, 2003
Summary of Tb – size and distance – CN2 dependencies
Best estimate: distance ~ 4-12 pc Angular size arcsec Tb~ K

12. 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 !

13. New extremely fast variations appear in 2004 and 2005.
They appear to come and go on ~ 1-2 month timescales. Probably intrinsic

14. Power spectra at 6cm in Feb 00, 03, 04, 05
Note the appearance of extra peaks at log (rad/s) ~ 10-2 and

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

16. The ‘polarization fun’ really started in summer 2002Q U V
~ 5 mJy polarized flux

18. Beautiful series of I,Q,U,V variations in winter/spring 05/06
22 Jan 2006
Frozen screen turbulence on >>hours timescale
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

19. 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

20. 8 GHz VLBI image 4-Jun-03 N-S displacement I - Q/U
Gabuzda, Moloney etal, in prep
8 GHz VLBI image 4-Jun-03
N-S displacement I - Q/U
about 600 arcsec at 8.4 GHz

21. Deriving the distance of the scattering screen to J1819+3845
Q 5 GHz (& 8.4 GHz ?)
U 5 GHz (& 8.4 GHz ?)
T  55m
VLBI separation at 8.4 GHz
 ~ 600 arcsec
I 5 GHz
T  20m
I GHz
= (55m+20m) x 30 km/s = cm / Dscreen = 600 /
 Dscreen  cm = 1.6  1 pc !!

22. A final useful constraint on the screen properties comes from (a dozen) widefield WSRT 21cm observations
1.25o x 1.25o field
200 sources S21cm > 100 Jy
Several ‘flat’ spectrum sources (quasars) with fluxdensities of about 1-20 mJy within 0.5o of J
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
to be continued

23. Derived properties of the screen:
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
Surrounding compact sources within 0.5o show little or no scintillations
 distance ~ 2 pc (~ 1019 cm)
Vtransverse relative to Sun ~ 35 km/s
 transverse dimensions > cm
 transverse dimensions < cm (0.01 x 1019 cm)
Distance from ~ pc to 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)

24. Line of sight to J1819+3845 crosses the edge of the local bubble at about 30 pc distance
Bhat et al 1998

25. 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 arcsec ( 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 ??