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