Beyond VLBI Micro-arcsecond Resolution with Inter-Stellar Scintillation D.L. Jauncey 1,2, J.E.J. Lovell 3, J.Y. Koay 4, J-P. Macquart 4, B.J. Rickett 5, H.E. Bignall 4, L. Kedziora-Chudczer 6, T. Pursimo 7, C. Reynolds 4, and R. Ojah 8 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 PKS 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 ~ 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……

PKS pattern time-delay ISS implies  -arcsecond sizes

During the discovery observations of PKS , 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 Observations  Four 72 hr epochs: Jan, May and Sep 2002 (96h), Jan 2003 during reconfiguration.  5 sub-arrays of 5 or 6 antennas each.  Core sample of 500 compact, flat-spectrum sources at 5 GHz  60 sec on-source per scan  ~6 scans per source per day (10,000 scans per epoch) Micro-Arcsecond Interstellar Scintillation-Induced Variability: MASIV

B B annual cycle high RMS

Integrated VLBI flux density curve of B , 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 afar How unlike the other ones Brighter than a billion suns Twinkle, twinkle, quasi-star How I wonder what you are.” George Gamow Newsweek Reprinted from the Proceedings of the First Texas Symposium on Relativistic Astrophysics