Flux Variations and Structural Changes in Extragalactic Radio Sources

Self Cite

“…Data prior to 1984 were used in a multifrequency analysis spanning a frequency range of 0.4−14.5 GHz (Padrielli et al 1987). Three distinct classes of variability were identified.…”

Section: Summary Of the Results Discussed In Previous Papersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A 15 years monitoring program at 408 MHz

Bondì

Padrielli

Fanti

et al. 1996

Self Cite

“…Further observations with VLBI show these features to contain components which are bright and compact enough to explain the variability at low frequency by propagation effects in the interstellar medium; see, for example, 3C 99, Mantovani et al (1990a). Sources such as these do not generally show any variability at high frequency (Padrielli et al 1987). …”

Section: And Altschulermentioning

confidence: 97%

VLA polarimetry of two extended radio galaxies

Junor

Mantovani

Morganti

et al. 2000

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Abstract. Multi-wavelength VLA observations of two extended radio galaxies, 0235 − 197 and 1203 + 043 are presented. There is some evidence from earlier studies that these two sources exhibit low frequency (< 1 GHz) variability. This work shows that both sources have linear polarizations, if any, below the detection limits at 320 MHz, so we cannot explain the variability as being due to instrumental polarization effects as has been suggested for 3C 159. Refractive scintillation may be the cause of the variability in 0235−197. This would require the existence of a bright, compact component in one of the hot spots seen in these observations. This is not implausible but the resolution of this observational program is insufficient to address that question. The radio source 1203+043 lacks any bright compact component thereby ruling out a refractive scintillation mechanism for its variability. Consequently, it is possible that claims of variability in this source are spurious. However, the 320 MHz VLA observations show that 1203+043 has an "X"-shaped radio structure. This is a rare morphology for the brightness distribution of a radio galaxy; the implications of this are examined.

“…In order to study the long-term variability behavior of extragalactic radio sources over a range of wavelengths, several monitoring programs have been carried out (Spangler & Cotton 1981;Aller et al 1985;Padrielli et al 1987;Salonen et al 1987;Bregman et al 1990;Teräsranta et al 1992;Bloom et al 1999). We have carried out flux monitoring of selected sources over a wide range of wavelengths with the Effelsberg 100 m radio telescope since 1994.…”

Section: Introductionmentioning

confidence: 99%

Long-term monitoring of selected radio sources

Peng

Kraus

Krichbaum

et al. 2000

Abstract. The Effelsberg 100 m radio telescope has been used, over a period of 5.5 years, to monitor the flux densities of 40 extragalactic radio sources, including the complete sample of 13 flat spectrum sources from the S5 Survey, and various other active sources. The study of their long-term variability characteristics at several wavelengths, the source light curves, spectra, and a statistical analysis are presented and discussed in this paper.