  We test the hypothesis that the disc cavity in the `transition disc' Oph IRS
48 is carved by an unseen binary companion. We use 3D dust-gas
smoothed-particle hydrodynamics simulations to demonstrate that marginally
coupled dust grains concentrate in the gas over-density that forms in in the
cavity around a low binary mass ratio binary. This produces high contrast ratio
dust asymmetries at the cavity edge similar to those observed in the disc
around IRS 48 and other transition discs. This structure was previously assumed
to be a vortex. However, we show that the observed velocity map of IRS 48
displays a peculiar asymmetry that is not predicted by the vortex hypothesis.
We show the unusual kinematics are naturally explained by the non-Keplerian
flow of gas in an eccentric circumbinary cavity. We further show that
perturbations observed in the isovelocity curves of IRS 48 may be explained as
the product of the dynamical interaction between the companion and the disc.
The presence of a $\sim$0.4 M$_{\odot}$ companion at a $\sim$10 au separation
can qualitatively explain these observations. High spatial resolution line and
continuum imaging should be able to confirm this hypothesis.
