Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Statistical analyses of long-term variability of AGN at high radio
  frequencies   We present a study of variability time scales in a large sample of Active
Galactic Nuclei at several frequencies between 4.8 and 230 GHz. We investigate
the differences of various AGN types and frequencies and correlate the measured
time scales with physical parameters such as the luminosity and the Lorentz
factor. Our sample consists of both high and low polarization quasars, BL
Lacertae objects and radio galaxies. The basis of this work is the 22 GHz, 37
GHz and 87 GHz monitoring data from the Metsahovi Radio Observatory spanning
over 25 years. In addition,we used higher 90 GHz and 230 GHz frequency data
obtained with the SEST-telescope between 1987 and 2003. Further lower frequency
data at 4.8 GHz, 8 GHz and 14.5 GHz from the University of Michigan monitoring
programme have been used. We have applied three different statistical methods
to study the time scales: The structure function, the discrete correlation
function and the Lomb-Scargle periodogram. We discuss also the differences and
relative merits of these three methods. Our study reveals that smaller flux
density variations occur in these sources on short time scales of 1-2 years,
but larger outbursts happen quite rarely, on the average only once in every 6
years. We do not find any significant differences in the time scales between
the source classes. The time scales are also only weakly related to the
luminosity suggesting that the shock formation is caused by jet instabilities
rather than the central black hole.

1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
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The categories of this paper are: math
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph