1. VLBI Observations of IDV Sources Brian Moloney Dr. Denise Gabuzda University College Cork

2. Summary

3. What is IDV? Intra-Day Variability: Rapid variations in the I and/or P flux on a timescale of hours How is it caused? Intrinsic Extrinsic

4. Intrinsic Within the source Implies compact size –Unfeasibly high Brightness Temperature 10 17 K which exceeds the Inverse Compton Limit of 10 12 K.

5. Extrinsic Outside the source Similar to twinkling stars

6. Previous Results J1819+3845’s IDV behaviour has been proven to arise due to Extrinsic effects. How? –Annual cycle –Time delay between 2 antennas Dennett-Thorpe J., De Bruyn A.G. 2003, A&A, 404, 113 Dennett-Thorpe J., De Bruyn A.G. 2002, Nature 415, 57

7. My Experiment Set of IDV sources in which the cause of variability is not yet certain. Observed at 8 & 15 GHz in 1997 VLBA + VLA

8. My Sources –0917+624 –0954+658 –1150+812 –2007+777 –1642+690 –0804+499

9. Plan Use VLA data to determine behaviour Use all I data to make VLBA map, then create slices in time of P data P VLA - P VLBI should be constant Identify if variability can be attributed to a certain area of polarisation on VLBI scales Analyse properties of varying region

10. Some Vector Subtraction

11. 0917+624 (VLA)

12. 0917+624 (VLBI)

13. 0917+624 Slices

14. 1642+690 (VLA)

15. 1642 +690 (VLBA)

16. Future Work More detailed analysis for 0917, 1642 Analyse time slices for other sources Model-fitting P data for time slices to better identify varying component and estimate its properties Compare results with expected behaviour for scintillation

17. Acknowledgements UCC Radio Astronomy Lab The Audience