This image is a mosaic of XMM-Newton's European Photon Imaging Camera’s (EPIC) observations of the central region of M31 as seen from 2000 to 2004.
The color coding is such that red displays X-ray photons received in the energy band 0.2-0.5 keV, green in the 0.5-1 keV band and blue in the 1-2 keV band. The positions of ten counterparts of optical novae detected in these images are indicated with circles and nova names. Nova names are given omitting the M31N prefix.
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.