  A rotated and harmonically trapped Bose gas with attractive interactions is
expected to either remain stationary or escape from the trap. Here we report
that, on the contrary, in an anharmonic trapping potential the Bose gas with
attractive interactions responds to external rotation very differently, namely
through center-of-mass motion or by formation of vortices, depending on the
strengths of the interaction and the anharmonic term in the trapping potential.
