Astronomy and Astrophysics, volume 480, 599-610 (2008/3-3)
Time variability of X-ray sources in the M 31 centre field.
STIELE H., PIETSCH W., HABERL F. and FREYBERG M.
Abstract (from CDS):
We present an extension to our XMM-Newton X-ray source catalogue of M31 containing 39 newly found sources. In order to classify and identify more of the sources we search for X-ray time variability in XMM-Newton archival data of the M31 centre field. As a source list we used our extended catalogue based on observations covering the time span from June 2000 to July 2004. We then determined the flux or at least an upper limit at the source positions for each observation. Deriving the flux ratios for the different observations and searching for the maximum flux difference we determined variability factors. We also calculated the significance of the flux ratios. Using hardness ratios, X-ray variability and cross correlations with catalogues in the X-ray, optical, infrared and radio regimes, we detected three super soft source candidates, one supernova remnant and six supernova remnant candidates, one globular cluster candidate, three X-ray binaries and four X-ray binary candidates. Additionally we identified one foreground star candidate and classified fifteen sources with hard spectra, which may either be X-ray binaries or Crab-like supernova remnants in M31 or background active galactic nuclei. The remaining five sources stay unidentified or without classification. Based on the time variability results we suggest six sources, which were formerly classified as ``hard'', to be X-ray binary candidates. The classification of one other source (XMMM31 J004236.7+411349) as a supernova remnant, has to be rejected due to the distinct time variability we found. We now classify this source as a foreground star.
galaxies: individual: M31 - X-rays: galaxies
VizieR on-line data:
<Available at CDS (J/A+A/480/599): table3.dat table5.dat refs.dat>
Tables 3,5, col(1): [PFH2005] NNN (Nos 857-895) added = Table 3, last col.: XMMM31 JHHMMSS.s+DDMMSS N=304.
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