1. Kinematic Studies of the IDV Quasar 0917+624 S. Bernhart T. P. Krichbaum L. Fuhrmann Max-Planck-Institut fϋr Radioastronomie, Bonn

2. EVN Symposium, Torun 26.09.2006 Outline Introduction of 0917+624 Motivation and description of the observations 2cm modelfit results Summary and future work

3. EVN Symposium, Torun 26.09.2006 The Quasar 0917+624 IDV Type II source at z=1.446 Episodically varying: high variability amplitudes from 1988 to 1999 (m~3-5%) Variability ceased in 1998 (Kraus et al. 1999) and 2000, since then m~0.5%

4. EVN Symposium, Torun 26.09.2006 The Quasar 0917+624 IDV Type II source at z=1.446 Episodically varying: high variability amplitudes from 1988 to 1999 (m~3-5%) Variability ceased in 1998 (Kraus et al. 1999) and 2000, since then m~0.5% T.P. Krichbaum/L. Fuhrmann

5. EVN Symposium, Torun 26.09.2006 Change of scintillating medium Flux decrease of scintillating component Jet precession Reduced IDV caused by component ejection: core size becomes larger than scattering size (typically ~0.05 – 0.07 mas for 0917, Rickett et al. 1995) -> quenched scintillation – could be possible explanation for 1998 (Krichbaum et al. 2002, Fuhrmann et al. 2002, Fuhrmann 2004) VLBI observations in order to find new components Possible Explanations for Reduced IDV Activity

6. EVN Symposium, Torun 26.09.2006 Observing Epochs VLBI: 1.3cm, 2cm, 6cm 2001-12-26 2002-03-27 2002-07-13 2003-04-10 additionally: MOJAVE-2cm: 2002-06-15 2003-06-15 2005-02-05 2005-06-15 2005-09-19 2006-08-09 VLBI-Observations at 2cm: 1999-11-20 2000-03-06 2000-11-30

7. EVN Symposium, Torun 26.09.2006 2cm modelfit maps S. Bernhart, in prep. beam 0.345 x 0.261 mas bpa -18° beam 0.2 x 0.2 mas

8. EVN Symposium, Torun 26.09.2006 Core Separation at 2cm S. Bernhart, in prep.

9. EVN Symposium, Torun 26.09.2006 Core Separation at 2cm Krichbaum et al. 2002/Fuhrmann 2004/Bernhart, in prep.

10. EVN Symposium, Torun 26.09.2006 Flux Density Monitoring S. Bernhart, in prep. time delay ~ 0.8 years between 2.8 cm and 11 cm (N. Kudryavzeva, priv. comm.) 1997.8 2000.08 2003.27

11. EVN Symposium, Torun 26.09.2006 Summary New components ejected in 2000 and 2003(?) No increase in the modulation index after component ejection Hypothesis of quenched scintillation not conclusive Future Work Continue single dish monitoring Further VLBI observations in order to test also different hypotheses