Abstract
Bridle and Purton1 have recently presented flux densities at 10.03 MHz for 126 radio sources. The ratio of their observed flux density (Sobs) to that expected (Sexp) from extrapolation of the high-frequency spectrum of each source is correlated with the galactic latitude of the source. For example, the geometric mean value of R = Sobs/Sexp among all sources in their list is 0.99 ± 0.04, but for sources within 15° of the galactic equator it is 0.70 ± 0.10. This attenuation of the 10 MHz flux densities near the galactic equator suggests that free-free absorption in the interstellar medium of the galaxy is significant at 10 MHz. Interstellar absorption of galactic background radiation has been reported at lower frequencies by several authors2–5.
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BRIDLE, A. 10 MHz Absorption in the Local Spiral Arm. Nature 221, 648–649 (1969). https://doi.org/10.1038/221648a0
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DOI: https://doi.org/10.1038/221648a0
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