Context : Short supersoft X-ray source ( SSS ) states ( durations \leq 100 days ) of classical novae ( CNe ) indicate massive white dwarfs that are candidate progenitors of supernovae type Ia .

Aims : We carry out a dedicated optical and X-ray monitoring program of CNe in the bulge of M 31 .

Methods : 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 .

Results : 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 .

Conclusions : The optical and X-ray light curves of M31N 2007-11a suggest a binary containing a white dwarf with M _ { WD } > 1.0 M _ { \sun } .