Post on 14-Jan-2016
VLBI Observations of IDV Sources
Brian Moloney
Dr. Denise Gabuzda
University College Cork
Summary
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
Intrinsic
• Within the source
• Implies compact size
– Unfeasibly high Brightness Temperature
• 1017 K which exceeds the Inverse Compton Limit of 1012 K.
Extrinsic
• Outside the source
• Similar to twinkling stars
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
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
My Sources
– 0917+624– 0954+658– 1150+812– 2007+777– 1642+690– 0804+499
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
Some Vector Subtraction
PVLBA
VLBA PVLA
VLA PDIFF
DIFF
0917+62416 ->1/0 8 -88 13 77 7 -301/0 ->1/6 14 85 22 76 10 -27
1150+8128 ->13 11 -79 21 86 13 -1713 ->18 13 -81 21 86 11 -1818 ->22 13 -71 22 74 21 -34
1642+6908 ->12 31 -25 39 -31 11 4112 ->15 27 -24 40 -32 16 4415 ->18 33 -21 36 -31 12 2518 ->23 23 -31 32 -39 12 35
2007+7778 ->16 80 -67 92 -70 14 716 ->21 62 -65 78 -65 16 2321 ->1/7 80 -68 96 -70 18 10
0917+624 (VLA)
0917+624 (VLBI)
0917+624 Slices
1642+690 (VLA)
1642 +690 (VLBA)
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
Acknowledgements
• UCC Radio Astronomy Lab
• The Audience