Wavelet analysis of a large sample of AGN at high radio frequencies

TL;DR

This study applies wavelet analysis to 80 AGNs at high radio frequencies, revealing non-periodic variability and demonstrating wavelets' superiority over Fourier methods in detecting persistent timescales.

Contribution

It introduces the use of wavelet analysis for AGN variability at high radio frequencies and compares its effectiveness to traditional Fourier methods.

Findings

AGNs are not periodic in their flux variability.

Wavelet analysis better detects when timescales are present.

Long-term changes in timescales are common.

Abstract

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. 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. 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.