Rapid variability of extragalactic radio sources

Publ. – Astron. Soc. Aust

Cimò

et al. 2002

Self Cite

There is new evidence which identifies seasonal changes of the variability time scale in intraday variable (IDV) sources with refractive interstellar scintillation effects. Such a RISS model takes the annual change of the Earth's velocity relative to the scattering medium into account. In September 1998 we found a remarkable prolongation of the variability time scale in the IDV source 0917+624 with only small variations in flux density during a period of 5 days. This was explained as a seasonal effect, in which the velocity vector of the Earth and the interstellar medium nearly cancelled. In order to further investigate the applicability of the model for 0917+624, we performed an Effelsberg 6 cm-flux monitoring program over the course of one year. Since September 2000, the source appears to be remarkably inactive and yet (May 2001) no return to its normal, faster and stronger variability pattern is observed. Here, our observational results and a possible explanation for the current quiescence are presented.

Section: Introductionmentioning

confidence: 99%

Annual Modulation in the Variability Properties of the IDV Source 0917+624?

Fuhrmann

Publ. – Astron. Soc. Aust

Cimò

et al. 2002

Self Cite

“…Correlated with the variations in P, the polarisation angle (PA) varies on the same timescale by typically a few to a few ten degrees . Sometimes, polarisation angle swings by 180 • are observed within hours (0917+62: Quirrenbach et al 1989;1150+81: Kochenov & Gabuzda 1999. A direct conclusion drawn from the polarisation IDV is a multiple component structure of the radio sources, with their sub-components being of different compactness and polarisation.…”

Section: Statistical Properties Of Idvmentioning

confidence: 99%

Intraday Variability in Northern Hemisphere Radio Sources

Publ. – Astron. Soc. Aust

Kraus

Fuhrmann

et al. 2002

Self Cite

We summarize results from flux density monitoring campaigns performed with the 100 meter radio-telescope at Effelsberg and the VLA during the past 15 yrs. We briefly discuss some of the statistical properties of the rapid variability from now more than 40 high declination sources, which show Intraday Variability (IDV). In general, IDV is more pronounced for sources with flat radio spectra and compact VLBI structures. The frequency dependence of the variability pattern varies with source and observing time. For 0917+62, we present new VLBI images, which suggest that the variability pattern is modified by the occurrence of new jet components. For 0716+71, we show the first detection of IDV at millimeter wavelengths (32 GHz). For the physical interpretation of the IDV phenomenon, a complex source and frequency dependent superposition of interstellar scintillation and source intrinsic variability should be considered.Comment: 8 pages, 4 figures, to appear in: `AGN Variability Across the Electromagnetic Spectrum', a conference held at CSIRO, Sydney, 25-29 June 2001. To be published by PAS

“…In parallel to the variability of the total flux density, variations of the polarized flux density and the polarization angle are observed frequently in many sources (Quirrenbach et al 1989;Gabuzda et al 2000a,b;Kraus et al 1999a,b,c). Both correlations (e.g.…”

Section: Introductionmentioning

confidence: 99%

Intraday variability in compact extragalactic radio sources

Kraus

Wegner

et al. 2003

A&A

Self Cite

118

162

Abstract. We present the data from 11 observing campaigns (carried out between 1989 and 1999) at the Effelsberg 100 m radio telescope to study Intraday Variability in Active Galactic Nuclei. Most of these observations were performed in total power and linear polarization. We give summary tables, light curves, and structure functions from these data sets. Due to the large number of individual observations, only examples of the lightcurves will be presented here; the complete set of figures will be accessible online . Intraday variations are present in nearly all sources (detected during at least one of the observing campaigns). Variations in total flux density are usually accompanied by similar variability of the linear polarization. In most cases, the latter variations are stronger and faster by up to a factor of two.