A new VLA/e-MERLIN limit on central images in the gravitational lens
  system CLASS B1030+074
  We present new VLA 22-GHz and e-MERLIN 5-GHz observations of CLASS B1030+074,
a two-image strong gravitational lens system whose background source is a
compact flat-spectrum radio quasar. In such systems we expect a third image of
the background source to form close to the centre of the lensing galaxy. The
existence and brightness of such images is important for investigation of the
central mass distributions of lensing galaxies, but only one secure detection
has been made so far in a galaxy-scale lens system. The noise levels achieved
in our new B1030+074 images reach 3 microJy/beam and represent an improvement
in central image constraints of nearly an order of magnitude over previous
work, with correspondingly better resulting limits on the shape of the central
mass profile of the lensing galaxy. Simple models with an isothermal outer
power law slope now require either the influence of a central supermassive
black hole, or an inner power law slope very close to isothermal, in order to
suppress the central image below our detection limit. Using the central mass
profiles inferred from light distributions in Virgo galaxies, moved to z=0.5,
and matching to the observed Einstein radius, we now find that 45% of such mass
profiles should give observable central images, 10% should give central images
with a flux density still below our limit, and the remaining systems have
extreme demagnification produced by the central SMBH. Further observations of
similar objects will therefore allow proper statistical constraints to be
placed on the central properties of elliptical galaxies at high redshift.
