The absolute spectrum of Cas A: an accurate flux density scale and a set of secondary calibrators.
Abstract
Summary. A new analysis of the absolute radio spectrum of Cassiopeia A is presented which uses the latest absolute measurements and takes account of the frequency dependence in the secular rate of decrease. The spectrum is established to an accuracy of 2 %. Between 0.3 and 30 GHz it is given by a flux density S1GHz=2723JY and a spectral index cc= -0.770 (epoch 1980.0). The absolute spectra of Cygnus A and Taurus A are also given. An accurate "semi-absolute" spectrum for Virgo A is established from direct accurate ratios to CasA and CygA yielding S1GHZ=28SJY, cc=-0.856 (valid for 0.4 v 25 GHz). This Virgo A spectrum is used as a basis for accurate relative spectra of a number of sources with simple spectra. These are proposed as secondary calibrators for the routine calibration of flux density measurements. Their spectral data are presented for the frequency range 0.4-15 GHz and are believed to have an absolute accuracy of about 5 %. Finally a comparison with other flux density scales is made and the paper concludes with some suggestions for future work. Key words: absolute radio spectrum Cassiopeia' A flux density scale flux density calibration - radio telescope calibration
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 1977
- Bibcode:
- 1977A&A....61...99B
- Keywords:
-
- Calibrating;
- Cassiopeia A;
- Radiant Flux Density;
- Radio Spectra;
- Radio Telescopes;
- Instrument Errors;
- Radio Astronomy;
- Secular Variations;
- Astronomy