ABSTRACT MOST extra-galactic radio sources have a spectrum which over a limited frequency range is of the form _S_αν−α, where _S_ is the flux density and ν is the frequency. The spectral

index α is usually constant over a considerable frequency range, which implies a straight spectrum when plotted logarithmically, the average value over all sources being 0.75 with a range

from about 0.2 to 1.3. For some sources, however, α changes slowly with frequency with the result that the spectra are concave or convex1–3. It is believed that the radiation is produced by

the synchrotron mechanism, where energy losses by the electrons can lead in time to an increase in the slope4,5 and where, in addition, different component sources may contribute to the

which had a low frequency cut-off due to synchrotron self-absorption7 and stimulated a search for other sources with similar spectra. Kellermann (personal communication) has recently

observed fourteen sources with irregular spectra, of which some have a tendency towards these latter characteristics, but so far there have been no published spectra similar to 3_C_ 84 and

3_C_ 279. Recent observations at the frequencies of 3,200, 6,600 and 10,600 MHz, however, using the 150 foot telescope of the Algonquin Radio Observatory, when combined with the observations

by other observers8–11, have shown that the source 4_C_ 50.11/NRAO 150 is of this form but with the addition of two apparent peaks at frequencies of about 350 and 9,000 MHz. The source is

included in the list by Kellermann, but details of the characteristics failed to show up because of the omission of low frequency observations and the new measurements between 5,000 and

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customer support SIMILAR CONTENT BEING VIEWED BY OTHERS A RADIO TRANSIENT WITH UNUSUALLY SLOW PERIODIC EMISSION Article 26 January 2022 ASTROPHYSICAL CONSTRAINTS FROM THE SARAS 3

NON-DETECTION OF THE COSMIC DAWN SKY-AVERAGED 21-CM SIGNAL Article 28 November 2022 ON THE DETECTION OF A COSMIC DAWN SIGNAL IN THE RADIO BACKGROUND Article 28 February 2022 REFERENCES *

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(1967). Article  ADS  Google Scholar  Download references AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Radio Astronomy Group, Queen's University, Kingston, Ontario V. A. HUGHES & 

R. V. POTTER Authors * V. A. HUGHES View author publications You can also search for this author inPubMed Google Scholar * R. V. POTTER View author publications You can also search for this

author inPubMed Google Scholar RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE HUGHES, V., POTTER, R. Spectrum of the Radio Source 4_C_ 50.11/NRAO 150.

_Nature_ 217, 832–833 (1968). https://doi.org/10.1038/217832a0 Download citation * Received: 06 December 1967 * Issue Date: 02 March 1968 * DOI: https://doi.org/10.1038/217832a0 SHARE THIS

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