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S. Trudolyubov, K. Borozdin (NIS-2, Los Alamos National Laboratory), W. Priedhorsky (NIS-DO, Los Alamos National Laboratory), R. Shirey (NIS-2, Los Alamos National Laboratory), K. Mason (Mullard Space Science Laboratory, University College, London, UK), M. Watson (University of Leicester, UK)
Using the data of monitoring Chandra and XMM observations, we study evolution of the variable and transient X-ray sources in the central region of M31. High sensitivity of the X-ray telescopes aboard allowed us to perform detailed analysis of the spectral properties of these sources and their evolution.
Several X-ray objects show a significant variability between individual Chandra and XMM observations and earlier ROSAT observations. We also report on the possible detection of the spectral transitions in some of these sources.
The transient sources demonstrate distinctly different types of X-ray variability and spectral evolution. XMMU J004234.1+411808 is most likely a black hole candidate based on the similarity of its X-ray light curve and spectra to typical transient low mass X-ray binaries observed in our Galaxy. The outburst of CXO J004242.0+411608 lasted longer than a year, which makes the source an unusual X-ray transient. The supersoft transient XMMU J004319.4+411759 is probably a classical nova-like system containing a magnetized, rapidly-spinning white dwarf.
We estimate a total rate of X-ray transient outbursts in the bulge of M31. The rate of the hard X-ray transients in the central part of the Andromeda Galaxy appears to be comparable to that of the central part of our own Galaxy.
The author(s) of this abstract have provided an email address for comments about the abstract: tsp@nis.lanl.gov