Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.sao.ru/cats/~satr/RFSymp/abs/15_Hovatta.ps Äàòà èçìåíåíèÿ: Mon Oct 9 11:14:23 2006 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 08:57:02 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: redshift survey

LONG­TERM RADIO TIME SCALES OF ACTIVE
GALACTIC NUCLEI
T. Hovatta 1 , M. Tornikoski 1 , M. Lainela 2 , E. Valtaoja 2 , I. Torniainen 1 ,
M.F. Aller 3 , H.D. Aller 3
1 Mets˜ahovi radio Observatory
Mets˜ahovintie 114 02540 Kylm˜al˜a, Finland
2 Tuorla Observatory, University of Turku, Finland
3 Department of Astronomy, University of Michigan
tho@kurp.hut.fi
We have studied long­term variability time scales of a large sample of Active Galactic
Nuclei at several frequencies between 4.8 and 230 GHz. The sample consists of 80 sources
from di#erent classes of AGN. In our sample we have quasars, BL Lacertae objects and
Radio Galaxies. Our sample consists of sources from the Mets˜ahovi monitoring programme
where a sample of compact extragalactic radio sources has been monitored for over 25
years. In addition we use lower frequency data from the University of Michigan monitoring
programme and data obtained from the SEST­telescope between 1986 and 2003.
We used the first order structure function, the discrete auto­correlation function and
the Lomb­Scargle periodogram to study the characteristic time scales of variability. We
were interested in finding di#erences and similarities between classes and frequencies. Also
the methods were compared in order to find the most e#cient one for di#erent purposes.
We have also compared the results of this study with earlier structure function analysis
by Lainela & Valtaoja (1993). In the earlier analysis the structure function was used to
study 42 sources from the Mets˜ahovi monitoring sample at 22 and 37 GHz frequencies. We
wanted to find out how the time scales have changed after the amount of monitoring data
has more than tripled.
The main conclusion of our study is that in these sources smaller variations happen also
in short time scales but larger outbursts only in time scales of many years. Therefore in
order to study how often sources are in active state and how long these flares typically last
the long­term monitoring is needed.
References
Lainela M., Valtaoja E.: ApJ, 1993, 416, 485.