Affiliation: | University of Manchester, NRAL, Jodrell Bank, Macclesfield, Cheshire SK11 9DL; Physics Department, Keele University, Keele, Staffordshire ST5 5BG; Astrophysics Research Institute, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF; Royal Military College of Canada, Kingston, Ontario K7K 5LO, Canada |