An Accurate Flux Density Scale from 1 to 50 GHz

TL;DR

This paper establishes a precise flux density scale for 1 to 50 GHz radio astronomy by combining VLA measurements, planetary models, and WMAP calibration, providing reliable standards and spectral expressions.

Contribution

It introduces an accurate flux density scale from 1 to 50 GHz using VLA data, planetary models, and WMAP calibration, with polynomial spectral expressions for key calibrators.

Findings

3C286 is the most suitable flux calibrator due to its stability and compactness.

Polynomial spectral flux density expressions are provided for key sources from 1983 to 2012.

The flux density scale achieves 1-3% absolute accuracy across 1-50 GHz.

Abstract

We develop an absolute flux density scale for cm-wavelength astronomy by combining accurate flux density ratios determined by the VLA between the planet Mars and a set of potential calibrators with the Rudy thermophysical emission model of Mars, adjusted to the absolute scale established by WMAP. The radio sources 3C123, 3C196, 3C286 and 3C295 are found to be varying at a level of less than ~5% per century at all frequencies between 1 and 50 GHz, and hence are suitable as flux density standards. We present polynomial expressions for their spectral flux densities, valid from 1 to 50 GHz, with absolute accuracy estimated at 1-3% depending on frequency. Of the four sources, 3C286 is the most compact and has the flattest spectral index, making it the most suitable object on which to establish the spectral flux density scale. The sources 3C48, 3C138, 3C147, NGC7027, NGC6542, and MWC349 show significant variability on various timescales. Polynomial coefficients for the spectral flux density are developed for 3C48, 3C138, and 3C147 for each of the seventeen observation dates, spanning 1983 through 2012. The planets Venus, Uranus, and Neptune are included in our observations, and we derive their brightness temperatures over the same frequency range.