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VLBI Observations of IDV Sources

This study focuses on Intra-Day Variability (IDV) in astronomical sources, exploring how rapid flux variations are caused by intrinsic and extrinsic factors. Previous results and future work on IDV sources are discussed, along with proposed methodologies for analysis.

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VLBI Observations of IDV Sources

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  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 • 1017 K which exceeds the Inverse Compton Limit of 1012 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 • PVLA - PVLBI 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

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