A combined optical and X-ray image of M31

This is an optical H-alpha image overplotted with contours from Chandra observations.

The optical image of the central area of M31 was taken with the 4-metre Kitt Peak National Observatory telescope during the Local Group Survey. The overlying contours are taken from merged observations of the Chandra High Resolution Camera in the imaging mode (HRC-I) carried out from December 2004 to February 2005.

The positions of 17 counterparts of optical novae detected in these images are indicated with circles and nova names. Nova names are given omitting the M31N prefix. The cross between the novae M31N 1995-09b and M31N 2004-11f indicates the centre of M 31 center, the point aimed at for observation.

It was detected that eleven out of the 34 novae that had exploded in the galaxy during the previous year were shining X-rays into space. An additional seven novae remained detectable in X-rays up to 10 years after outburst.

The conclusion of the scientists is that the number of X-ray-detected optical novae is higher than previously expected, an important indication of the physical properties of these systems. The short-lived optical novae form a new ‘live fast and die young’ class of X-ray sources that would have been overlooked in the past by surveys carried out only every six months.

To investigate further, the team have been awarded more XMM-Newton and Chandra observing time. They now plan to monitor M31’s novae every ten days for several months, starting in November 2007.