We describe a method performing w-projection using the fast Gauss transform of Strain (1991). We derive the theoretical performance, and simulate the actual performance for a range of w for a canonical array. While our implementation is dominated by
overheads, we argue that this approach could for the basis of a higher-performing algorithms with particular application to the Square Kilometer Array.
Searching for dispersed radio pulses in interferometric data is of great scientific interest, but poses a formidable computational burden. Here we present two efficient, new antenna-coherent solutions: The Chirpolator and The Chimageator. We describe
the equations governing both techniques and propose a number of novel optimizations. We compare the implementation costs of our techniques with classical methods using three criteria: the operations rates (1) before and (2) after the integrate-and-dump stage, and (3) the data rate directly after the integrate-and-dump stage. When compared with classical methods, our techniques excel in the regime of sparse arrays, where they both require substantially lower data rates, and The Chirpolator requires a much lower post-integrator operations rate. In general, our techniques require more pre-integrator operations than the classical ones. We argue that the data and operations rates required by our techniques are better matched to future supercomputer architectures, where the arithmetic capability is outstripping the bandwidth capability. Our techniques are, therefore, viable candidates for deploying on future interferometers such as the Square Kilometer Array.
We describe a 22-year survey for variable and transient radio sources, performed with archival images taken with the Molonglo Observatory Synthesis Telescope (MOST). This survey covers $2775 unit{deg^2}$ of the sky south of $delta < -30degree$ at an
observing frequency of 843 MHz, an angular resolution of $45 times 45 csc | delta| unit{arcsec^2}$ and a sensitivity of $5 sigma geq 14 unit{mJy beam^{-1}}$. We describe a technique to compensate for image gain error, along with statistical techniques to check and classify variability in a population of light curves, with applicability to any image-based radio variability survey. Among radio light curves for almost 30000 sources, we present 53 highly variable sources and 15 transient sources. Only 3 of the transient sources, and none of the variable sources have been previously identified as transient or variable. Many of our variable sources are suspected scintillating Active Galactic Nuclei. We have identified three variable sources and one transient source that are likely to be associated with star forming galaxies at $z simeq 0.05$, but whose implied luminosity is higher than the most luminous known radio supernova (SN1979C) by an order of magnitude. We also find a class of variable and transient source with no optical counterparts.
