  In recent years, searches of archival X-ray data have revealed galaxies
exhibiting nuclear quasi-periodic eruptions with periods of several hours.
These are reminiscent of the tidal disruption of a star by a supermassive black
hole, and the repeated, partial stripping of a white dwarf in an eccentric
orbit around a ~10^5 solar mass black hole provides an attractive model. A
separate class of periodic nuclear transients, with significantly longer
timescales, have recently been discovered optically, and may arise from the
partial stripping of a main-sequence star by a ~10^7 solar mass black hole. No
clear connection between these classes has been made. We present the discovery
of an X-ray nuclear transient which shows quasi-periodic outbursts with a
period of weeks. We discuss possible origins for the emission, and propose that
this system bridges the two existing classes outlined above. This discovery was
made possible by the rapid identification, dissemination and follow up of an
X-ray transient found by the new live \swift-XRT transient detector,
demonstrating the importance of low-latency, sensitive searches for X-ray
transients.
