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Published online by Cambridge University Press: 26 May 2016
We present radio continuum spectra for nearly 200 Galactic supernova remnants (SNRs) from 220 known and included in Green's (1998) catalog. Spectra plotting is an “on—line” procedure of the CATS database http://cats.sao.ru/ and it could plot quite accurate spectra with the thermal plasma free—free absorption in fitting the spectra accounted for: to indicate the presence of extended ionized medium along the line of sight.
We did not find considerable correlation between spectral index and Galactic coordinates l, b of SNRs. An analysis of 190 spectra showed that 78 SNRs (40 %) have clear low-frequency turnover caused, apparently, by absorption in the thermal foreground of the Milky Way. The turnover frequency vτ=1 for these SNRs has mean value near 30 MHz do not correlate with the Galactic coordinates. But the frequency has significant correlation with the distance to SNR, defined from ∑ — D relation.