Search

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.

Over 13600 continuum observations of extragalactic sources are presented. These observations of 157 sources at 22, 37 and 87 GHz more than doubles the millimeter observations of these sources. The data are between 1990.5 and 1995.5, and combined with our earlier published data they form a 15 year database.

The properties of compact extragalactic radio sources are investigated using a sample of 27 sources extensively observed at millimeter frequencies. It is suggested that the radio variability of all AGN, independent of their classification, can be understood in terms of growing and decaying shocks in a jet.

BL Lacertae has been the target of four observing campaigns by the Whole Earth Blazar Telescope (WEBT) collaboration. In this paper we present UBVRI light curves obtained by theWEBT from 1994 to 2002, including the last, extended BL Lac 2001 campaign. A total of about 7500 optical observations performed by 31 telescopes from Japan to Mexico have been collected, to be added to the ∼15 600 observations of the BL Lac Campaign 2000. All these data allow one to follow the source optical emission behaviour with unprecedented detail. The analysis of the colour indices reveals that the flux variability can be interpreted in terms of two components: longer-term variations occurring on a fewday time scale appear as mildly-chromatic events, while a strong bluer-when-brighter chromatism characterizes very fast (intraday) flares. By decoupling the two components, we quantify the degree of chromatism inferring that longer-term flux changes imply moving along a ∼0.1 bluerwhen- brighter slope in the B − R versus R plane; a steeper slope of ∼0.4 would distinguish the shorter-term variations. This means that, when considering the long-term trend, the B-band flux level is related to the R-band one according to a power law of index ∼1.1. Doppler factor variations on a “convex” spectrum could be the mechanism accounting for both the long-term variations and their slight chromatism. Reig Torres, Pablo, Pablo.Reig@uv.es

From several southern hemisphere radio-wavelength monitoring programs, we have compiled multi-wavelength observations of a number of both EGRET-detected sources and sources with similar radio-properties that have not been detected by EGRET. The radio observations were made at 0.8, 2, 5, 8, 90 and 230 GHz, though not all sources were monitored at all wavelengths. The data are compared with EGRET data to the end of Cycle 4 (October 1995) in an effort to confirm previously reported correlations between activity at radio wavelengths and EGRET detections, and to investigate whether the non-EGRET-detected sources were in radio- and gamma-ray–quiet phases during this period.

Quasars have been monitored with the Metsahovi Radio Telescope since 1980 at 22 GHz and 37 GHz. During these years we have recorded numerous outbursts in our sample. Some of the outbursts are simple in nature, while others also seem to have fine structure. Can the outbursts be modelled in a simple way?

Quasars have been monitored with the Metsähovi Radio Telescope since 1980 at 22 GHz and 37 GHz. During these years we have recorded numerous outbursts in our sample. Some of the outbursts are simple in nature, while others also seem to have fine structure. Can the outbursts be modelled in a simple way?

We analyze the time variability of compact radio sources at 22 and 37 GHz by using a structure function analysis. Our monitoring program in Metsahovi, Finland, includes a complete sample of bright, flat-spectrum extragalactic compact radio sources. For the structure function analysis we have selected 42 best-observed sources from this sample. In this subsample we have 14 BL Lac objects, 13 high-polarization quasars, 12 low-polarization quasars, two galaxies, and one empty field source. The structure function analysis exhibits very similar slopes for all sources, which is consistent with there being one basic physical mechanism of millimeter variability for all compact radio sources