Transcript VLBI Observations of IDV Sources

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+624
16 ->1/0
1/0 ->1/6
8
14
-88
85
13
22
77
76
7
10
-30
-27
1150+812
8 ->13
13 ->18
18 ->22
11
13
13
-79
-81
-71
21
21
22
86
86
74
13
11
21
-17
-18
-34
1642+690
8 ->12
12 ->15
15 ->18
18 ->23
31
27
33
23
-25
-24
-21
-31
39
40
36
32
-31
-32
-31
-39
11
16
12
12
41
44
25
35
2007+777
8 ->16
16 ->21
21 ->1/7
80
62
80
-67
-65
-68
92
78
96
-70
-65
-70
14
16
18
7
23
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