The ATCA Intraday Variability Survey

For my PhD project I studied Intraday Variability (IDV) of the flux density of extragalactic radio sources at giga-hertz frequencies.
We have surveyed a large sample of compact, flat-spectrum radio sources with Australia Telescope Compact Array (ATCA) during 1993-1994. The sample contains 118 sources, relatively uniformly distributed over the southern sky for b>10 degrees.
The sample listed in Table A along with identifications, galactic coordinates, redshift and source structure information, contains 89 (75.4%) quasars, 13 (11%) BL Lacs, 7 (5.9%) galaxies, 1 (0.8%) stellar object and 8 (6.7%) unidentified sources.
We have looked into the statistical properties of IDV and attempted to interpretate of observed IDV as the result of interstellar scintillations.

Some results of the survey

The most rapid and strongest IDV source: PKS 0405-385

We have observed extreme and unusual variability in the radio flux density of the quasar PKS 0405-385 on timescales of less than an hour. Inferred brightness temperature is of the order to 10^{21} K under an assumption of an intrinsic variability. This is nine orders of magnitude larger than the inverse Compton limit for a static synchrotron source.
We interpret such variability as interstellar scintillation and conclude that the source has to be as small as 5 microarcsec.

The new intraday variable sources discovered in the survey

The list of sources which show modulation indices exceeding 3 sigma (in bold) for any frequency in any of the two observing sessions: May 94 and August 94 (table2)

Statistical issues:

This is only a summary of results from the survey. The detailed discussion is provided in my thesis. If you would like to obtain more detailed information about the survey you can E-mail me on

The copy of my PhD thesis can be accessed here.

References relevant to the IDV subject can be found here
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Last updated: 30-August-2000