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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
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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
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J1819+3845: a ~21m quasar at z=0.55 peaking at 30-40 GHz
Peaking around GHz in 1999!
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Variability through the seasons (1999/2002):
a sample of early lightcurves
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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 !
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….but excellent fit with anisotropic scintels (14:1) in PA ~ 85o
~Nov 20
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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
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Dennett-Thorpe & de Bruyn, 2002
Variable timedelay of ~ 100 seconds proof of scintillation ! 7 Jan 2001
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However, the velocity solution is degenerate in (VRA,VDec) for very anisotropic turbulence
1 February
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The ‘preferred’ velocity solution implies Jan-March motion perpendicular to the very elongated scintels (~100,000 x 1000,000 km) Barney Rickett, (priv comm)
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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
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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 !
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New extremely fast variations appear in 2004 and 2005.
They appear to come and go on ~ 1-2 month timescales. Probably intrinsic
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Power spectra at 6cm in Feb 00, 03, 04, 05
Note the appearance of extra peaks at log (rad/s) ~ 10-2 and
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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)
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The ‘polarization fun’ really started in summer 2002
Q U V ~ 5 mJy polarized flux
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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
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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
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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
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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 !!
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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
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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)
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Line of sight to J1819+3845 crosses the edge of the local bubble at about 30 pc distance
Bhat et al 1998
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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 ??
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