Letter to the Editor

The very short supersoft X-ray state of the classical nova M31N 2007-11a ^*,**

¹ Max-Planck-Institut für extraterrestrische Physik, 85748 Garching, Germany e-mail: mhenze@mpe.mpg.de
² Departament de Física i Enginyeria Nuclear, EUETIB (UPC/IEEC), Comte d'Urgell 187, 08036 Barcelona, Spain
³ European Southern Observatory (ESO), 85748 Garching, Germany
⁴ INAF - Napoli, Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁵ International Centre for Relativistic Astrophysics, Piazzale della Repubblica 2, 65122 Pescara, Italy
⁶ Institut de Ciències de l'Espai (CSIC-IEEC), Campus UAB, Fac. Ciències, 08193 Bellaterra, Spain
⁷ Department of Physics and Astronomy, Clemson University, Clemson, SC 29634-0978, USA
⁸ Steward Observatory, 933 North Cherry Avenue, Tucson, AZ 85721, USA

Received: 23 December 2008
Accepted: 13 March 2009

Abstract

Context. 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.

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 .