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X-ray Sources in Normal Galaxies
XMM-Newton observations of Local Group galaxies are well suited to study the X-ray source population and diffuse emission in nearby spiral galaxies. The results are important to interpret X-ray data from similar more distant galaxies and allow us to study the differences between younger (e.g. high mass XRBs) and older (low mass XRBs, globular cluster sources) populations.
We have homogeneously analyzed all archival XMM-Newton EPIC observations of the Local Group galaxies M 31 and M 33 and detected 856 and 408 sources, respectively. The sources are identified or classified using X-ray hardness ratio and information from other wavelengths. Within the galaxies we find supersoft sources (SSSs), supernova remnants (SNRs), and X-ray binaries (XRBs). In addition there are foreground stars from the Milky Way and objects in the background (galaxies, cluster of galaxies and active galactic nuclei (AGN)). In total we more than doubled the number of sources in the fields and detected many new SSS, XRBs and SNRs in the galaxies.
Fig 1: XMM-Newton EPIC low background three colour images combining PN and MOS cameras for M 31. Red, green and blue show respectively (0.2-1, 1-2, 2-12) keV bands. The optical extent of the galaxies is indicated by D25 ellipses. The images are smoothed with a Gaussian of 20" FWHM. The insert in the M 31 image shows a factor 3 zoom-in on the centre area (5" smoothing). SSS, thermal SNRs and foreground stars show up in red and yellow, plerionic type SNRs, XRBs and AGN in green , white or blue.
Fig 2: Hardness ratio (HR) diagram of M 33 sources detected by XMM-Newton. Shown as dots are only sources with HR errors smaller than 0.2. Fourground stars and candidates are marked as big and small stars, AGN as crosses, SSSs as triangles, SNRs as hexagons, X-ray binaries as squares. In addition HRs from measured objects in the Galaxy or Magellanic Clouds or determined from model spectra for the source classes are shown by filled symbols. SSSs clearly separate by their HR1. Thermal SNRs and foreground stars cover the same area in the HR2-HR1 diagram and can be separated using optical information. XRBs, plerionic type SNRs and AGN do not separate in the HR diagrams and all show hard HRs.
Transient X-ray sources in the central area of M 31
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Last update: 2010-02-01 by H. Steinle
Contact person: W. Pietsch and F. Haberl
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