Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979a%26as...36..359f&link_type=abstract
Astronomy and Astrophysics Supplement Series, vol. 36, June 1979, p. 359-369.
Astronomy and Astrophysics
Astrophysics
37
Extragalactic Radio Sources, Low Frequencies, Microwave Spectra, Radiant Flux Density, Variability, Calibrating, Radio Telescopes, Scintillation
Scientific paper
The East-West arm of the Northern Cross near Bologna, Italy, has been used to observe 42 extragalactic radio sources at 408 MHz approximately once per month for a period approaching 3 years. The results of this monitoring program are given. Fifteen sources are found to be variable and three to be possibly variable. In spite of the relatively low observing frequency where source variability predicted from simple expanding relativistic cloud models should be negligible, changes in flux density of as much as 44% have been detected. The severe problems in interpreting the physical conditions in the radio sources implied by these variations of large amplitude on short time scales are discussed. It is unclear at present if the low frequency variations are related to high frequency events. However, there appears to be a marked tendency for low frequency (nu less than 1 GHz) variables to also show variability at high frequencies (nu greater than 1 GHz).
Fanti Roberto
Ficarra A.
Mantovani Fabio
Padrielli Lucia
Weiler Kurt
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