The low frequency array and the transient and variable radio sky

Abstract

This thesis addresses the topic of exploring and characterising the transient and variable radio sky, using both existing radio telescopes, and the next generation of radio facilities such as the Low Frequency Array (LOFAR). Studies of well known variable radio sources are presented in conjunction with blind searches of parameter space for unknown sources. Firstly, a three year campaign to monitor the low luminosity Active Galactic Nucleus NGC 7213 in the radio and X-ray bands is presented. Cross-correlation functions are used to calculate a global time lag between inflow (X-ray) and outflow (radio) events. Through this work the previously established scaling relationship between core radio and X-ray luminosities and black hole mass, known as the ‘fundamental plane of black hole activity’ is also explored with respect to NGC 7213. Secondly, the technical and algorithmic procedures to search for transient and variable radio sources within radio images is presented. These algorithms are intended for deployment on the LOFAR telescope, however, they are heavily tested in a blind survey using data obtained from the VLA archive. Through this work an upper limit on the rate of transient events on the sky at GHz frequencies is placed and compared with those found from other dedicated transient surveys. Finally, the design, operation and data reduction procedure for the Low Frequency Array, which will revolutionise our understanding of low frequency time domain astrophysics is explored. LOFAR commissioning observations are reduced and searched for transient and variable radio sources. The current quality of the calibration limits accurate variability studies, however, two unique LOFAR transient candidates that are not present in known radio source catalogues are explored (including multi-wavelength followup observations). In the conclusion to this thesis the parameter space that future radio telescopes may probe - including the potential rates of such events - is presented. At the nano-Jansky level up to 107 transients deg?2 yr?1 are predicted, which will form an unprecedented torrent of data, followup and unique physics to classify

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