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Beyond VLBIMicro-arcsecond Resolution with
Inter-Stellar Scintillation
D.L. Jauncey1,2, J.E.J. Lovell3, J.Y. Koay4,
J-P. Macquart4 , B.J. Rickett5, H.E. Bignall4, L. Kedziora-Chudczer6, T. Pursimo7,
C. Reynolds4, and R. Ojah8
1: CASS, 2: MSO, 3: Utas, 4: ICRA, 5: UCSD, 6: UNSW, 7: NOT, 8: GSFC
Intra-Day Variables from the beautiful MPI 100 m Bonn Machine.
But is it intrinsic or extrinsic?
Where it got going………
In 1996 at the ATCA, as part of her IDV Survey,
Lucyna Kedziora-Chudczer found
PKS0405-385 the first of the 3 rapid
variables
8.4 GHz
4.8 GHz
Here’s the full 3 days of ATCA data at 8.4, 4.8, 2.4 and 1.4 GHz. The pattern of strong variability at 5 and 8 GHz,
and decreasing variability at the lower frequencies
suggests ISS as the cause. Otherwise Tb ~ 1021 K !!!
8.4 GHz
4.8 GHz
2.4 GHz
1.4 GHz
How to tell the difference between
intrinsic variability and
inter-stellar scintillation?
through one of the more elegant “VLBI” experiments undertaken
between the ATCA and the VLA……
PKS1257-326 pattern
time-delay
ISS implies -arcsecond
sizes
During the discovery observations of PKS1257-326, Hayley found this beautiful
annual-cycle, again, clearly it’s ISS!
What next?Our objective was to obtain a sample
of ~ 100 scintillators for reliable statistics. At the time (2000), this implied a sample size of ~ 500 flat-spectrum sources. The only instrument capable of achieving this
is the VLA. 5 GHz is in the weak scattering regime and is where the VLA
works well.
Micro-Arcsecond Scintillation Induced Variability Survey
MASIV
MASIV: VLA ObservationsMASIV: VLA Observations Four 72 hr epochs: Four 72 hr epochs:
Jan, May and Sep 2002 (96h), Jan 2003 during reconfiguration.Jan, May and Sep 2002 (96h), Jan 2003 during reconfiguration. 5 sub-arrays of 5 or 6 antennas each.5 sub-arrays of 5 or 6 antennas each.
Core sample of 500 compact, flat-spectrum sources at 5 GHz Core sample of 500 compact, flat-spectrum sources at 5 GHz 60 sec on-source per scan 60 sec on-source per scan ~6 scans per source per day (10,000 scans per epoch)~6 scans per source per day (10,000 scans per epoch)
Micro-Arcsecond Interstellar Scintillation-Induced Variability: MASIV
B0059+581 B1156+295
annual cycle high RMS
Integrated VLBI flux density curve of B1156+295, obtained by averaging the correlated flux density at projected baselines shorter than 100 M.
from Savolainen & Kovalev 2008
ISS effects on VLBI
Important implications for Space VLBI……
Galactic Distribution
The high WHAM correlation strongly supports ISS
Redshift dependence
For more on this you’ll have to wait for Hayley Bignall’s talk tomorrow…..
“Twinkle, twinkle, quasi-star Biggest puzzle from afarHow unlike the other ones Brighter than a billion sunsTwinkle, twinkle, quasi-star How I wonder what you are.”
George GamowNewsweek
Reprinted from the Proceedings of the
First Texas Symposium on Relativistic Astrophysics