The XMM-Newton SSC survey of the Galactic plane

Many different classes of X-ray sources contribute to the Galactic landscape at high energies. Although the nature of the most luminous X-ray emitters is now fairly well understood, the population of low-to-medium X-ray luminosity (LX = 1027−34 erg s−1) sources remains much less studied, our knowledge being mostly based on the observation of local members. The advent of wide field and high sensitivity X-ray telescopes such as XMM-Newton now offers the opportunity to observe this low-to-medium LX population at large distances. We report on the results of a Galactic plane survey conducted by the XMM-Newton Survey Science Centre (SSC). Beyond its astrophysical goals, this survey aims at gathering a representative sample of identified X-ray sources at low latitude that can be used later on to statistically identify the rest of the serendipitous sources discovered in the Milky Way. The survey is based on 26 XMM-Newton observations, obtained at |b| S ) − log S curves in the soft and hard bands. In the soft band, the majority of the sources are positively identified with active coronae and the fraction of stars increases by about one order of magnitude from b = 60◦ to b = 0◦ at an X-ray flux of 2 × 10−14 erg cm−2 s−1. The hard band is dominated by extragalactic sources, but there is a small contribution from a hard Galactic population formed by CVs, HMXB candidates or γ-Cas-like systems and by some active coronae that are also detected in the soft band. At b = 0◦ the surface density of hard sources brighter than 1 × 10−13 erg cm−2 s−1 steeply increases by one order of magnitude from l = 20◦ to the Galactic centre region (l = 0.9◦)