Gyroscopic Gravitational Memory

We study the motion of a gyroscope located far away from an isolated gravitational source in an asymptotically flat space-time. As seen from a local frame `tied to distant stars', the gyroscope precesses when gravitational waves cross its path, resulting in a net `orientation memory' that carries information on the wave profile. The effect is related to asymptotic symmetries: at leading order in the inverse distance to the source, the precession rate coincides with the (covariant) dual mass aspect, providing a celestially local measurement protocol for dual supertranslation charges. Furthermore, the net gyroscopic memory is derived from flux-balance equations for superrotations and contains an extra flux generating electric-magnetic duality. The spin memory effect is reproduced as a special case.Comment: 16 pages, 2 figures (V2: added references and minor corrections