4 Conclusions

In this paper we present results obtained from XMM-Newton  PV observations of M 31. Two observations separated by half of a year were carried out in June and December of 2000. This paper is the second paper in the series describing results of these observations.

Significant variability of individual sources was detected both between the two XMM  observations and in comparison with earlier results of other missions. At least $\sim$15% of the sources appear to be variable, and we consider this value to be a conservative lower limit.

A new bright transient source was detected during the observation of June 25 but faded before the December observation. Probably it is an LMXB transient source, similar to a handful of such sources observed in our Galaxy, most of which are supposed to harbour black holes.

Another transient source, first detected by Chandra  (G2000), was bright during both XMM-Newton  observations. The flux of the source did not change significantly in observations separated by six months, which is not typical for Galactic X-ray transients but is reminiscent of the behavior of the black hole candidate GRS 1716-249 during its 1993-1994 outbursts (Sunyaev et al. 1994; Revnivtsev et al. 1998).

X-ray pulsations with period of $\sim$865.5 s and quasi-sinusoidal pulse profile were detected from one of the supersoft sources in our field. It was bright during the June observation, but had faded such that it became undetectable in December. The period of the detected pulsations is the shortest among known SSSs. A likely source of the pulsations is a magnetized rapidly spinning white dwarf; however, the luminosity of the source is much higher than for typical CV systems. The detected X-ray flux may be generated by steady nuclear burning in a post-nova stage of a classical or symbiotic nova.

Acknowledgements

We thank all the members of the XMM-Newton  teams for their work building, operating, and calibrating the powerful suite of instruments on-board. We also thank the referee, Dr. T. Oosterbroek, for his helpful comments.