Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986natur.319..471s&link_type=abstract
Nature (ISSN 0028-0836), vol. 319, Feb. 6, 1986, p. 471-473.
Astronomy and Astrophysics
Astronomy
13
Astronomical Maps, Extragalactic Radio Sources, Radio Emission, Radio Spectra, Astronomical Models, Galactic Evolution, Relativistic Plasmas
Scientific paper
The extragalactic radio source Cygnus A has been mapped at 81.5 MHz using a two-element interferometer with variable orientation and spacing. This is the lowest frequency at which the radio source has been mapped with sufficient resolution to resolve the bridge of emission joining the two outer lobes, and the data provide new information about the radiation spectrum. By comparing the map with one produced at 2.7 GHz, the two-point spectral index is measured as a function of distance along the source axis. The age of the radio source is estimated by using a model in which two oppositely directed beams ram their way out through the surrounding medium, depositing relativistic plasma as they do so. Synchrotron radiation losses are more severe at high frequencies, causing a break in the spectrum which occurs at progressively lower frequencies as the plasma ages. The analysis suggests that Cyg A is about 3 Myr old.
Duffett-Smith P. J.
Rees W. G.
Spinks M. J.
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