Measurements of Radio Sources in the 3C Catalogue.
D. J. Crampin, David S. Heeschen, I. I. K. Pauliny‐Toth, Campbell M. Wade · The Astronomical Journal · 1963
The new 300-ft paraboloidal antenna of the Xational Radio Astronomy Observatory is being used to make measurements of the positions and flux densities of all the sources in the 3C list (Edge, D. 0., Shakeshaft, J. R., McAdam, W. B., Baldwin, J. E., and Archer, S., Mem. Roy. Astron. Soc. 68, 37,1959) at frequencies of 750 and 1400 Mcsec. (The beamwidth at these frequencies is 18,5 and 10,0, respectively.) At 1400 Mcsec, a source with a flux density of about 0.3 X 10-26 W m-2 cps 1 gives a signal equal to the peak-to-peak noise level. For a source with a spectral index of 1, this corresponds to a flux density of about 3 X 10-26 W m 2 cps-1 at the frequency of the 3C survey (159 Mc$sec). Since the lower flux limit of the 3C catalogue is 8X10-26 W m-2 cps-1, all sources included in it should be observable. These expectations have been confirmed by the observations made so far. Sources at the lower flux limit of the 3C list can be detected easily and their positions can be measured with an accuracy better than 2' in declination and 2S in right ascension. It should therefore be possible in the present program to improve the accuracy in the declinations of the positions given in the 3C list, to remove ambiguities due to possible lobe shifts, and to obtain spectral indices for a large number of sources. The present results have confirmed the general reliability of the 3C catalogue. About 20% of the sources in the 3C list are shown as "possibly lobeshifted"; about 30% of the sources observed so far are in lobe-shifted positions. Some sources, such as 3C 398, have been resolved into two or more components, and in a number of others, the brightness distribution has been found to be asymmetrical.