Fast radio flashes observed with LOFAR prototypes
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Nijmegen : Radboud University, Department of Astrophysics, IMAPP
Number of pages
Nijmegen, 22 januari 2008
Promotores : Falcke, H.D.E., Kuijpers, J.M.E. Co-promotores : Groot, P.J., Hörandel, J.R., Zarka, P.
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This thesis consists of a detailed analysis of several observations with prototype stations of the Low Frequency Array (LOFAR). Chapter 1 introduces the field of radio astronomy, briefly describes the radio telescopes which were used and discusses radio frequency interference (RFI) and important tools for signal processing. Chapter 2 describes observations of Jupiter radio bursts, which were analyzed for propagation effects and cross-correlated with simultaneous observations of the Nançay Decametric Array. In Chapter 3, cosmic rays are introduced and the detection of radio emission from cosmic-ray air showers is described. The 4th chapter contains the description and discussion of radio spectra obtained from cosmic-ray air shower emission. In Chapter five, a technique to determine the directions of the measured radio emission from cosmic-ray events is discussed and compared to the directions provided by KASCADE. Some conclusions of the research results presented in this thesis are:- The source regions of Jupiter-Io S-bursts do not extend an angular size of 4 arcseconds.- Long baseline interferometry can be performed at low frequencies on periods from tens to hundreds of milliseconds with a baseline of about 700km, in spite of phase shifts introduced by variations in ionospheric propagation characteristics.- The electric field from high-energy cosmic-ray air showers has a steep spectrum decreasing in the LOPES band from 40MHz to 80MHz with a spectral index of -1.0, lying slightly above the slope obtained from Monte Carlo simulations based on air showers simulated with CORSIKA.- The directional accuracy of an interferometer, such as LOPES, was found to be strongly dependent on the curvature radius used for the near-field beam-forming.- Observations of events during thunderstorm activity confirmed theoretical predictions of a geoelectric effect.
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