  Short supersoft X-ray source (SSS) states (durations < 100 days) of classical
novae (CNe) indicate massive white dwarfs that are candidate progenitors of
supernovae type Ia. We carry out a dedicated optical and X-ray monitoring
program of CNe in the bulge of M 31. We discovered M31N 2007-11a and determined
its optical and X-ray light curve. We used the robotic Super-LOTIS telescope to
obtain the optical data and XMM-Newton and Chandra observations to discover an
X-ray counterpart to that nova. Nova M31N 2007-11a is a very fast CN,
exhibiting a very short SSS state with an appearance time of 6-16 days after
outburst and a turn-off time of 45-58 days after outburst. The optical and
X-ray light curves of M31N 2007-11a suggest a binary containing a white dwarf
with a mass greater than one solar mass.
