Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.sao.ru/cats/~satr/RFSymp/abs/15_Hovatta.pdf Дата изменения: Mon Oct 9 11:39:02 2006 Дата индексирования: Tue Oct 2 09:33:21 2012 Кодировка: Поисковые слова: annular solar eclipse

LONG-TERM RADIO TIME SCALES OF ACTIVE GALACTIC NUCLEI
T. Hovatta 1 , M. Tornikoski 1 , M. Lainela 2 , E. Valtao ja 2 , I. Torniainen 1 , M.F. Aller 3 , H.D. Aller 3 MetsЁ vi radio Observatory aho MetsЁ vintie 114 02540 KylmЁ a, Finland aho alЁ Tuorla Observatory, University of Turku, Finland Department of Astronomy, University of Michigan tho@kurp.hut.fi
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We have studied long-term variability time scales of a large sample of Active Galactic Nuclei at several frequencies b etween 4.8 and 230 GHz. The sample consists of 80 sources from different classes of AGN. In our sample we have quasars, BL Lacertae ob jects and Radio Galaxies. Our sample consists of sources from the MetsЁ vi monitoring programme aho where a sample of compact extragalactic radio sources has b een monitored for over 25 years. In addition we use lower frequency data from the University of Michigan monitoring programme and data obtained from the SEST-telescop e b etween 1986 and 2003. We used the first order structure function, the discrete auto-correlation function and the Lomb-Scargle p erio dogram to study the characteristic time scales of variability. We were interested in finding differences and similarities b etween classes and frequencies. Also the metho ds were compared in order to find the most efficient one for different purp oses. We have also compared the results of this study with earlier structure function analysis by Lainela & Valtao ja (1993). In the earlier analysis the structure function was used to study 42 sources from the MetsЁ vi monitoring sample at 22 and 37 GHz frequencies. We aho 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 happ en 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 long-term monitoring is needed. References Lainela M., Valtao ja E.: ApJ, 1993, 416, 485.