Cosmic: Microarcsecond Resolution with a 30 Meter Radio Telescope

Interstellar scintillation has been conclusively demonstrated to be the principal cause of the intraday variability (IDV) observed in the centimeter-wavelength emission of many active galactic nuclei. A few sources show large amplitude modulation in their flux density on a timescale of hours. However, the majority of IDV sources exhibit variability on timescales of a day or more. Some sources have been found to show an annual cycle in the pattern of their variability. Such an annual cycle occurs because the relative speeds of the Earth and the interstellar medium change as the Earth orbits the Sun. To search for these annual variations, as well as to follow the source evolution, requires a dedicated instrument; the necessary amounts of observing time are beyond the capability of the National Facility instruments. Here we describe the scientific motivation for and present an outline of the COSMIC (Continuous Single-Dish Monitoring of Intraday Variability at Ceduna) project, which uses the University of Tasmania's 30m diameter radio telescope at Ceduna, which has been monitoring the flux density of a number of the stronger southern scintillators at 6.65 GHz since 2003 March. © 2005. The American Astronomical Society. All rights reserved.