Abstract
Högbom and Shakeshaft1 have recently presented evidence for a secular variation of the intensity of radio emission from the source Cassiopeia A. Their observations, made at a frequency of 81.5 Mc./s. over a period of 12 years, suggest that the flux density of Cassiopeia A relative to that of Cygnus A is decreasing at a rate of about 1 per cent per annum. This type of measurement may be sensitive to unknown systematic instrumental effects, and the importance of the result makes independent confirmation desirable.
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References
Högbom, J. A., and Shakeshaft, J. R., Nature, 189, 561 (1961).
Westerhout, G., B.A.N., 14, 215 (1958).
Mezger, P. G., Z. Astrophys., 46, 234 (1958).
Heeschen, D. S., Astrophys. J. (in the press).
Hagen, J. P., McClain, E. F., and Hepburn, N., Proc. Inst. Rad. Eng., 42, 1811 (1954).
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HEESCHEN, D., MEREDITH, B. Secular Variation of the Flux Density of the Radio Source Cassiopeia A. Nature 190, 705–706 (1961). https://doi.org/10.1038/190705a0
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DOI: https://doi.org/10.1038/190705a0
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