Long-term variability of extragalactic radio sources in the Planck Early Release Compact Source Catalogue

1 Infrared Processing and Analysis Centre, California Institute of Technology, Pasadena, CA 91125, USA e-mail: [email protected] 2 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany 3 Instituto de Física de Cantabria (CSIC-Universidad de Cantabria), Avda. de los Castros s/n, Santander, Spain 4 Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK 5 California Institute of Technology, Pasadena, California, USA 6 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany 7 Haverford College Astronomy Department, 370 Lancaster Avenue, Haverford, Pennsylvania, USA 8 Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands