Wavelet analysis of a large sample of AGN at high radio frequencies*
Metsähovi Radio Observatory, TKK, Helsinki University of Technology, Metsähovintie 114, 02540 Kylmälä, Finland e-mail: email@example.com
2 Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
3 Department of Physics, 20140 University of Turku, Finland
Accepted: 18 June 2008
Aims. We have studied the characteristic timescales of 80 AGNs at 22, 37 and 90 GHz examining the properties of the wavelet method and comparing them to traditional Fourier-based methods commonly used in astronomy.
Methods. We used the continuous wavelet transform with the Morlet wavelet to study the characteristic timescales. We also gain information when the timescale is present in the flux curve and if it is persistent or not.
Results. Our results show that the sources are not periodic and changes in the timescales over a long time are common. The property of wavelets to be able to distinguish when the timescale has been present is superior to the Fourier-based methods. Therefore we consider it appropriate to use wavelets when the quasi-periodicities in AGNs are studied.
Key words: galaxies: active / methods: statistical / radio continuum: galaxies
© ESO, 2008