  The M 31 nova M31N 2008-12a was recently found to be a recurrent nova (RN)
with a recurrence time of about 1 year. This is by far the fastest recurrence
time scale of any known RNe. Our optical monitoring programme detected the
predicted 2014 outburst of M31N 2008-12a in early October. We immediately
initiated an X-ray/UV monitoring campaign with Swift to study the
multiwavelength evolution of the outburst. We monitored M31N 2008-12a with
daily Swift observations for 20 days after discovery, covering the entire
supersoft X-ray source (SSS) phase. We detected SSS emission around day six
after outburst. The SSS state lasted for approximately two weeks until about
day 19. M31N 2008-12a was a bright X-ray source with a high blackbody
temperature. The X-ray properties of this outburst were very similar to the
2013 eruption. Combined X-ray spectra show a fast rise and decline of the
effective blackbody temperature. The short-term X-ray light curve showed
strong, aperiodic variability which decreased significantly after about day 14.
Overall, the X-ray properties of M31N 2008-12a are consistent with the average
population properties of M 31 novae. The optical and X-ray light curves can be
scaled uniformly to show similar time scales as those of the Galactic RNe U Sco
or RS Oph. The SSS evolution time scales and effective temperatures are
consistent with a high-mass WD. We predict the next outburst of M31N 2008-12a
to occur in autumn 2015.
