Markku Lainela

Total Flux Density Variations in Extragalactic Radio Sources. I. Decomposition of Variations into Exponential Flares

We show that 22 and 37 GHz total flux density variations in compact extragalactic radio sources can to a good accuracy be modeled by superposition of a small number of flare components. Both the rise and the decay of these flares are exponential, with a characteristic decay timescale 1.3 times longer than the rise timescale. The properties of the individual model flares derived from these flux decompositions are in agreement with data obtained from VLBI observations of the corresponding new shock components. The total flux density decompositions can be used to search correlations between radio and other regimes, to calibrate and to interpret VLBI observations, and to derive physical parameters of the shocks. In particular, the associated brightness temperatures of the flares can be used to estimate the amount of Doppler boosting in each source and, using additional VLBI data, to derive the intrinsic brightness temperatures, the Lorentz factors and the viewing angles of the sources.

Twenty years monitoring of extragalactic sources at 22, 37 and 87 GHz

Long term monitoring results from mid 1995 to the end of 2000 of quasar observations at 22, 37 and 87 GHz done at the Metsahovi radio observatory are presented. Approximately 15 700 observations are published here.

Statistical analyses of long-term variability of AGN at high radio frequencies

Aims. 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. Methods. 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. Results. 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.

The 65 Day Period in 3C 66A during Bright State

Historically, 3C 66A has been considered a relative quiescent blazar. For that reason, 3C 66A was selected as a comparison source for OJ 287 in the OJ-94 project. However, after more detailed observation it turns out that the variability of 3C 66A itself is very interesting. We have analyzed the entire project data set of 3C 66A from fall of 1993 to spring of 1998 by using structure function analysis, Deeming periodograms, Scargle periodograms, and the folded light curves. Here we present the first preliminary evidence for the 65 day period in 3C 66A observed during the bright state. Our analysis indicates that this period is slowly slowing down. We will also discuss the possible physical mechanism producing the observed periodicity.

Radio spectra and variability of gigahertz-peaked spectrum radio sources and candidates

We have made long-term, high radio frequency observations of southern and equatorial active galactic nuclei (AGNs). After complementing these data with data from the literature, we have constructed the radio spectra of these sources and searched for sources with inverted spectra in the gigahertz range. We have identified 12 new sources with spectral shapes resembling those of the gigahertz-peaked spectrum (GPS) sources and eight other sources with inverted spectral parts in the gigahertz region. Several of these new GPS-source candidates have high (≥10 GHz) peak frequencies in the observers frame, and they all exhibit strong long-term variability. We have also studied the variability behavior of known GPS sources, mainly quasar-type sources. All of the 14 sources included in our sample show moderate to extremely high radio variability, and at least 12 of them are also variable in the millimeter domain. Long-term monitoring of these sources shows that some of them have spectral shapes resembling those of classical variable flat-spectrum sources, indicating that some of these sources have been misidentified as GPS sources when only sparsely sampled data have been available. On the other hand, four of the variable sources show persistent GPS-type spectra at all stages of activity, suggesting that at least some of the GPS sources can be variable.

Possible Identifications for Southern EGRET Sources

We have made total flux density observations at high radio frequencies (90 and 230 GHz) of 12 southern AGNs that were classified as possible EGRET identifications in the Third EGRET Catalog. Our observations confirm the blazar nature of five of them. We have also studied sources that we considered good candidates for AGN counterparts of previously unidentified EGRET sources and that had not been observed in the millimeter domain before. Four of them showed millimeter range activity that may be related to their gamma-ray activity, making them good candidates for the EGRET source identification.

The High Radio Frequency Spectra and Variability of Southern Flat-Spectrum Radio Sources

We have complemented observations of the millimeter spectra (90 and 230 GHz) of a complete sample of Southern flat-spectrum active galactic nuclei. We discuss the overall shape of the radio spectrum of these sources and identify two new gigahertz-peaked spectrum sources with unusually high peak frequencies (10–20 GHz). We also discuss the variability behavior in the millimeter domain.

Cluster analyses of gigahertz-peaked spectrum sources with self-organising maps

Context. Gigahertz-peaked spectrum (GPS) sources and high frequency peakers (HFPs) are among the smallest of active galactic nuclei currently believed to represent the earliest phases in the evolution of extragalactic radio sources. Recently there has been evidence of contamination by other types of radio sources among the GPS and HFP samples, but the confirmed GPS sources or HFPs also seem to form a very heterogeneous population. Aims. We study the statistical clustering of the GPS sources and the HFPs by taking as many source parameters as possible to find homogeneous groups among the sources. We expect the clustering to give us insight into the physical parameters that play a role in different source populations. Methods. We have collected a sample of 206 GPS sources and HFPs from the literature and gathered a massive database of various source properties, such as the redshift, the size, the polarization, the magnitudes, and the properties of the radio continuum. To visualize and to cluster these multidimensional data we used self-organising maps (SOM), which are neural networks trained by an unsupervised algorithm. We have classified the sources with an auxiliary classification to trace the locations of different types of radio continuum spectra on the map. Results. The sources form distinctive clusters on the map, which is supported by the accordant organisation of the non-numerical parameters not used in the analysis, such as the radio morphology and the optical identification. Our results confirm that the blazars contaminating the GPS and the HFP samples are physically different from the genuine GPS sources and HFPs, and they should be excluded from the samples. The genuine GPS sources form various clusters, which indicates the existence of different subpopulations, besides the expected galaxy-quasar dualism.

Long term radio variability of AGN

Talvikki Hovatta∗,1 Merja Tornikoski,1 Harry J. Lehto,2,3 Elina Nieppola,1 Esko Valtaoja,2,3 Markku Lainela,2 Ilona Torniainen,1 Anne Lahteenmaki1 Margo F. Aller4 and Hugh D. Aller4 1Metsahovi Radio Observatory, TKK, Helsinki University of Technology Metsahovintie 114, 02540 Kylmala, Finland 2Tuorla Observatory, University of Turku Vaisalantie 20, 21500 Piikkio, Finland 3Department of Physics, University of Turku 20140 University of Turku, Finland 4Department of Astronomy, University of Michigan Ann Arbor, MI 48109, USA E-mail: tho@kurp.hut.fi