  We conduct one-dimensional stellar evolutionary numerical simulations under
the assumption that an efficient dynamo operates in the core of massive stars
years to months before core collapse and find that the magnetic activity
enhances mass loss rate and might trigger binary interaction that leads to
outbursts. We assume that the magnetic flux tubes that the dynamo forms in the
inner core buoy out to the outer core where there is a steep entropy rise and a
molecular weight drop. There the magnetic fields turn to thermal energy, i.e.,
by reconnection. We simulate this energy deposition where the entropy steeply
rises and find that for our simulated cases the envelope radius increases by a
factor of 1.2-2 and luminosity by about an order of magnitude. These changes
enhance the mass loss rate. The envelope expansion can trigger a binary
interaction that powers an outburst. Because magnetic field amplification
depends positively on the core rotation rate and operates in cycles, not in all
cases the magnetic activity will be powerful enough to change envelope
properties. Namely, only a fraction of core-collapse supernovae experiences
pre-explosion outbursts.
