  Ultracold fermionic atoms in an optical lattice, with a sudden
position-dependent change (a quench) in the effective dispersion relation, have
been proposed by Rodr\'iguez-Laguna et al. as an analogue spacetime test of the
Unruh effect. We provide new support for this analogue by analysing a massless
scalar field on a $(1+1)$-dimensional continuum spacetime with a similar
quench: an early time Minkowski region is joined at a constant time surface,
representing the quench, to a late time static region in which left and right
asymptotically Rindler domains are connected by a smooth negative curvature
bridge. We show that the quench is energetically mild, and late time static
observers, modelled as a derivative-coupling Unruh-DeWitt detector, see
thermality, in a temperature that equals the Unruh temperature for observers in
the asymptotic Rindler domains. The Unruh effect hence prevails, despite the
energy injected into the field by the quench and despite the absence of a late
time Killing horizon. These results strengthen the motivation to realise the
experimental proposal.
