The 154 MHz radio sky observed by the Murchison Widefield Array: noise,
  confusion and first source count analyses
  We analyse a 154 MHz image made from a 12 h observation with the Murchison
Widefield Array (MWA) to determine the noise contribution and behaviour of the
source counts down to 30 mJy. The MWA image has a bandwidth of 30.72 MHz, a
field-of-view within the half-power contour of the primary beam of 570 deg^2, a
resolution of 2.3 arcmin and contains 13,458 sources above 5 sigma. The rms
noise in the centre of the image is 4-5 mJy/beam. The MWA counts are in
excellent agreement with counts from other instruments and are the most precise
ever derived in the flux density range 30-200 mJy due to the sky area covered.
Using the deepest available source count data, we find that the MWA image is
affected by sidelobe confusion noise at the ~3.5 mJy/beam level, due to
incompletely-peeled and out-of-image sources, and classical confusion becomes
apparent at ~1.7 mJy/beam. This work highlights that (i) further improvements
in ionospheric calibration and deconvolution imaging techniques would be
required to probe to the classical confusion limit and (ii) the shape of
low-frequency source counts, including any flattening towards lower flux
densities, must be determined from deeper ~150 MHz surveys as it cannot be
directly inferred from higher frequency data.
