Variability time scales from long term monitoring

Details Variability time scales from long term monitoring Variability time scales from long term monitoring

Oct 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006enig.confe...2h&link_type=abstract

Proceedings of the 8th ENIGMA meeting, held in Espoo, Finland, September 6-8, 2006, Eds: T.Hovatta, E.Nieppola and I.Torniainen,

Physics

Scientific paper

We have been studying the long term variability time scales of a large sample of Active Galactic Nuclei (AGNs), which have been monitored in the Metsähovi radio observatory at 22, 37 and 87 GHz. In the sample we have 80 sources from different AGN classes including BL lacertae objects (BLOs), highly polarized quasars (HPQs), low polarisation quasars (LPQs) and radio galaxies (GALs). In our study we used several frequency bands between 4.8 and 230 GHz. The lower frequency data at 4.8-14.5 GHz are from the University of Michigan Radio Observatory (UMRAO) and the higher frequency data at 90 and 230 GHz mostly from the SEST telescope. We used the structure function, discrete autocorrelation function and the Lomb-Scargle periodogram to derive the time scales. Motivation for using many methods, was to study the differences between the methods and the reliability of the results. Our results reveal that time scales shorten with increasing frequency. When considering the observational time scales we did not find significant differences between the AGN types. After redshift correcting the results, the time scales between the flares showed significant difference between the BLOs and the quasars. This means that the rate at which shocks are ejected into the jet is different for BLOs and quasars.

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