9C spectral-index distributions and source-count estimates from 15 to 93
  GHz - a re-assessment
  In an earlier paper (2007), we used follow-up observations of a sample of
sources from the 9C survey at 15.2 GHz to derive a set of spectral-index
distributions up to a frequency of 90 GHz. These were based on simultaneous
measurements made at 15.2 GHz with the Ryle telescope and at 22 and 43 GHz with
the Karl G. Jansky Very Large Array (VLA). We used these distributions to make
empirical estimates of source counts at 22, 30, 43, 70 and 90 GHz. In a later
paper (2013), we took data at 15.7 GHz from the Arcminute Microkelvin Imager
(AMI) and data at 93.2 GHz from the Combined Array for Research in
Millimetre-wave Astronomy (CARMA) and estimated the source count at 93.2 GHz.
In this paper, we re-examine the data used in both papers and now believe that
the VLA flux densities we measured at 43 GHz were significantly in error, being
on average only about 70 per cent of their correct values. Here, we present
strong evidence for this conclusion and discuss the effect on the source-count
estimates made in the 2007 paper. The source-count prediction in the 2013 paper
is also revised. We make comparisons with spectral-index distributions and
source counts from other telescopes, in particular with a recent deep 95 GHz
source count measured by the South Pole Telescope. We investigate reasons for
the problem of the low VLA 43-GHz values and find a number of possible
contributory factors, but none is sufficient on its own to account for such a
large deficit.
