Resumo

BORKA, D.; BORKA JOVANOVIć, V.  e  UROšEVIć, D.. Spectra of the HB 21 supernova remnant: Evidence of sprectrum flattening at the low frequencies. Rev. mex. astron. astrofis [online]. 2012, vol.48, n.1, pp.53-60. ISSN 0185-1101.

We use observations of the continuum radio emission at 1420, 820, 408, 34.5 and 22 MHz to estimate the mean brightness temperatures of the HB 21 supernova remnant (SNR) at five frequencies. We also present mean spectral index of HB 21. The spectra of HB 21 are estimated from mean temperatures versus frequency plots for 1420, 820, 408, 34.5 and 22 MHz. We also present T - T plots of three frequency pairs: between 1420-34.5, 1420-22, 34.5-22 MHz. We notice flatter spectral indices at frequencies below 408 MHz. Probably this is due to the absorption by thermal plasma at low frequencies.

Palavras-chave : ISM [individual objects (HB 21)]; radiation mechanisms [non-thermal]; radiation mechanisms [thermal]; radio continuum [general]; surveys.

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