We propose that the intermediate luminosity optical transient NGC 300 OT2008-1 was powered by a mass transfer episode from an extreme asymptotic giant branch star to a main sequence (MS) companion. We find a remarkable similarity in the shapes of the light curves of the several months long NGC 300 OT2008-1 outburst, of the three-month long 2002 enigmatic outburst of the B star V838 Mon, and the twenty-year long Great Eruption of the massive binary system Eta Carinae that occurred in the 19th century. Their similar decline properties hint to a common energy source: a gravitational energy that is released by accretion onto an MS star. These events populate a specific strip in the total energy versus outburst duration diagram. The strip is located between novae and supernovae. We add recent transient events to that diagram and find them to occupy the same strip. This suggests that some intermediate luminosity optical transients are powered by accretion onto a compact object (not necessarily an MS star). These transients are expected to produce bipolar ejecta as a result of the geometry of the accretion process.
stars: individual: NGC 300 OT - stars: mass-loss - stars: variables: general - stars: winds, outflows - supernovae: general