Vacuum interpretation for supergravity M-branes

We derive a new classical duality between the three-block truncated 11D supergravity and the 8D vacuum gravity with two commuting Killing symmetries. The supergravity four-form field is generated via an inverse dualisation of the corresponding Killing two-forms in six dimensions. The existence of the 11D unbroken supersymmetries for this class of solutions is shown to be equivalent to the existence of covariantly constant spinors in eight dimensions. Thus any solution to the vacuum Einstein equations in eight dimensions depending on six coordinates and admitting Killing spinors have supersymmetric 11D-supergravity counterparts. Using this duality we derive some new brane solutions to 11D-supergravity including 1/4 supersymmetric intersecting M-branes with a NUT parameter and a dyon solution joining the M2 and M5-branes intersecting at a point.