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 (L_X = 10²⁷ - 10³⁴ erg/s) 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 L_X population at large distances. This study reports 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| < 20 degrees, distributed over a large range in Galactic longitudes and covering a summed area of 4 deg². The flux limit of this survey is 2 x 10^-15 erg/cm²/s in the soft (0.5 - 2 keV) band and 1 x 10^-14 erg/cm²/s in the hard (2 - 1 2keV) band. A total of 1319 individual X-ray sources have been detected. Using optical follow-up observations supplemented by cross-correlation with a large range of multi-wavelength archival catalogs, the authors identify 316 X-ray sources. This constitutes the largest group of spectroscopically identified low-latitude X-ray sources at this flux level. The majority of the identified X-ray sources are active coronae with spectral types in the range A to M at maximum distances of ~1 kpc. The number of identified active stars increases towards late spectral types, reaching a maximum at K. Using infrared colors, the authors classify 18% of the stars as giants. The observed distributions of F_X/F_V, X-ray and infrared colors indicates that their sample is dominated by a young (100 Myr) to intermediate (600 Myr) age population with a small contribution of close main-sequence or evolved binaries. The authors find other interesting objects such as cataclysmic variables (d ~ 0.6 - 2 kpc), low-luminosity high-mass stars (likely belonging to the class of Gamma-Cas-like systems, d ~ 1.5 - 7 kpc), T Tauri and Herbig-Ae stars. A handful of extragalactic sources located in the highest Galactic latitude fields could be optically identified. For the 20 fields observed with the EPIC pn camera, the authors have constructed log N(>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 degrees to b = 0 degrees at an X-ray flux of 2 x 10^-14 erg/cm²/s. 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 Gamma-Cas-like systems and by some active coronal stars that are also detected in the soft band. At b = 0 degrees, the surface density of hard sources brighter than 1 x 10^-13 erg/cm²/s steeply increases by one order of magnitude from l = 20 degrees to the Galactic center region (l = 0.9 degrees). This HEASARC table contains 739 X-ray sources detected in the 26 different fields observed in this study and listed in Tables 8 - 33, inclusive, of the reference paper. These 739 sources have the best XMM quality, i.e. the summary flag sum_flag which contains information about flags set automatically and manually for a given source is zero, meaning that there are no negative flags for the source detection, have either a 2MASS, USNO, GSC, or SDSS counterpart, whatever the probability of identification is, or have some information via SIMBAD or the authors own

This table contains the final optical identifications of the medium-depth (~60 ks), contiguous (2 degree²) XMM-Newton survey of the COSMOS field. XMM-Newton has detected ~1800 X-ray sources down to limiting fluxes of ~5 x 10^-16, ~3 x 10^-15, and ~7 x 10^-15 erg cm^-2 s^-1 in the 0.5-2 keV, 2-10 keV, and 5-10 keV bands, respectively (~1 x 10^-15, ~6 x 10^-15, and ~1 x 10^-14 erg cm^-2 s^-1, in the three bands, respectively, over 50% of the area). The work is complemented by an extensive collection of multi-wavelength data from 24 microns to UV, available from the COSMOS survey, for each of the X-ray sources, including spectroscopic redshifts for >~50% of the sample, and high-quality photometric redshifts for the rest. The XMM-Newton and multi-wavelength flux limits are well matched: 1760 (98%) of the X-ray sources have optical counterparts, 1711 (~95%) have IRAC counterparts, and 1394 (~78%) have MIPS 24 um detections. Thanks to the redshift completeness (almost 100%) the authors were able to constrain the high-luminosity tail of the X-ray luminosity function confirming that the peak of the number density of log L_X > 44.5 active galactic nuclei (AGNs) is at z ~ 2. Spectroscopically identified obscured and unobscured AGNs, as well as normal and star-forming galaxies, present well-defined optical and infrared properties. The authors devised a robust method to identify a sample of ~150 high-redshift (z > 1), obscured AGN candidates for which optical spectroscopy is not available. They were able to determine that the fraction of the obscured AGN population at the highest (L_X > 10⁴⁴ erg s^-1) X-ray luminosity is ~15%-30% when selection effects are taken into account, providing an important observational constraint for X-ray background synthesis. The authors studied in detail the optical spectrum and the overall spectral energy distribution of a prototypical Type 2 QSO (source number 2028), caught in a stage transitioning from being starburst dominated to AGN dominated, which was possible to isolate only thanks to the combination of X-ray and infrared observations. This table was created by the HEASARC in July 2010 based on the electronic version of Table 2 from the paper which was obtained from the Astrophysical Journal web site.

The HEASARC has made some changes to this material in order to make it more compliant with CDS/IAU Nomenclature and HEASARC table standards:

(i) The original naming convention suggested by the authors used a prefix of 'XMMC_' and the J2000.0 RA and Dec position in decimal degrees to 10^-5 degrees precision, e.g., XMMC_150.10515+1.98082'; the HEASARC has replaced these names by alternative new ones (in the alt_name parameter) of the form 'XMMU JHHMMSS.s+DDMMSS' where the prefix is the usual one for XMM-Newton sources and the remainder of the field is the J2000.0 equatorial coordinates truncated to 0.1 seconds of time in RA and to 1 arcsecond in Declination;

(ii) We have used for the alt_name parameter the naming convention recommended by the Dictionary of Nomenclature of Celestial Objects for XMM-COSMOS sources, viz. the "XMMC' prefix and the source (XID) number, e.g., "XMMC 2028'. This is a service provided by NASA HEASARC .

This table contains a source catalog based on XMM-Newton observations of the bright Local Group spiral galaxy M 31. In an analysis of XMM archival observations of M 31, the authors studied the population of X-ray sources (X-ray binaries, supernova remnants) down to a 0.2-4.5 keV luminosity of 4.4 x 10³⁴ erg/s. EPIC hardness ratios and optical and radio information were used to distinguish between different source classes. The survey detected 856 sources in an area of 1.24 square degrees. The authors correlated their sources with earlier M 31 X-ray catalogs and used information from optical, infra-red and radio wavelengths. As sources within M 31, they detected 21 supernova remnants (SNR) and 23 SNR candidates, 18 supersoft source (SSS) candidates, 7 X-ray binaries (XRBs) and 9 XRB candidates, as well as 27 globular cluster sources (GlC) and 10 GlC candidates, which most likely are low mass XRBs within the GlC. Comparison to earlier X-ray surveys revealed transients not detected with XMM-Newton, which add to the number of M 31 XRBs. There are 567 sources classified as hard, which might either be XRBs or Crab-like SNRs in M 31 or background AGN. The number of 44 SNRs and candidates more than doubles the X-ray-detected SNRs. 22 sources are new SNR candidates in M 31 based on X-ray selection criteria. Another SNR candidate might be the first plerion detected outside the Galaxy and the Magellanic Clouds. On the other hand, six sources are foreground stars and 90 are foreground star candidates, one is a BL Lac-type active galactic nucleus (AGN) and 36 are AGN candidates, one source coincides with the Local Group galaxy M 32, one with a background galaxy cluster (GCl) and another is a GCl candidate, all sources which are not connected with M31. In a second paper, the authors presented an extension to the original 2005 XMM-Newton X-ray source catalog of M 31 which contained 39 newly found sources. These sources have been added to the original 856 sources to make a combined catalog of 895 X-ray sources which is contained herein. This table was originally created by the HEASARC in May 2005 based on the CDS table J/A+A/434/483/ file table2.dat (sources numbered 1 to 856). It was updated by the HEASARC in June 2008 by adding the 39 sources from the CDS table J/A+A/480/599/ file table3.dat (sources numbered 857 to 895). This is a service provided by NASA HEASARC .

This table contains a source catalog based om XMM-Newton observations of the nearby galaxy M 33. In an XMM-Newton raster observation of this bright Local Group spiral galaxy, the authors studied the population of X-ray sources (X-ray binaries, supernova remnants) down to a 0.2-4.5 keV luminosity limit of 10³⁵ erg/s, more than a factor of 10 deeper than earlier ROSAT observations. European Photon Imaging Camera (EPIC) hardness ratios and optical and radio information are used to distinguish between different source classes. The survey detects 408 sources in an area of 0.80 square degree. The authors correlated these newly detected X-ray sources with earlier M 33 X-ray catalogs and information from optical, infra-red and radio wavelengths. As M 33 sources, theydetect 21 supernova remnants (SNR) and 23 SNR candidates, 5 super-soft sources and 2 X-ray binaries (XRBs). There are 267 sources classified as hard, which may either be XRBs or Crab-like SNRs in M 33 or background AGN. The 44 confirmed and candidate SNRs more than double the number of X-ray detected SNRs in M 33. 16 of these are proposed as SNR candidates from the X-ray data for the first time. On the other hand, there are several sources not connected to M 33: five foreground stars, 30 foreground star candidates, 12 active galactic nucleus candidates, one background galaxy and one background galaxy candidate. Extrapolating from deep field observations, 175 to 210 background sources are expected in this field. This indicates that about half of the sources which were detected are actually within M 33. This table was created by the HEASARC in October 2004 based on CDS table J/A+A/426/11/table3.dat This is a service provided by NASA HEASARC .

The authors have obtained a deep 8-field XMM-Newton mosaic of M33 covering the galaxy out to the D₂₅ isophote and beyond to a limiting 0.2-4.5 keV unabsorbed flux of 5 x 10^-16 erg cm^-2 s^-1 (L > 4 x 10³⁴ erg s^-1 at the 817 kpc distance of M33). These data allow complete coverage of the galaxy with high sensitivity to soft sources such as diffuse hot gas and supernova remnants (SNRs). In the reference paper, the authors describe the methods they used to identify and characterize 1296 point sources in the 8 fields. They compare their resulting source catalog to the literature, note variable sources, construct hardness ratios, classify soft sources, analyze the source density profile, and measure the X-ray luminosity function (XLF). As a result of the large effective area of XMM-Newton below 1 keV, the survey contains many new soft X-ray sources. The radial source density profile and XLF for the sources suggest that only ~15% of the 391 bright sources with L > 3.6 x 10³⁵ erg s^-1 are likely to be associated with M33, and more than a third of these are known SNRs. The log(N)-log(S) distribution, when corrected for background contamination, is a relatively flat power law with a differential index of 1.5, which suggests that many of the other M33 sources may be high-mass X-ray binaries. Finally, the authors note the discovery of an interesting new transient X-ray source, which they are unable to classify. The list of XMM-Newton observations used for this survey is given in Table 1 of the reference paper. The data reduction and source detection techniques are described in Section 3 of this same reference. The unabsorbed energy conversion factors (ECF) values for different energy bands and instruments that were used in this paper are as follows (the units are 10¹¹ counts cm² erg^-1):

 HEASARC Energy Band MOS1 MOS2 PN band prefix (keV) Med Filter Med Filter Thin Filter sb0_ 0.2-0.5 0.5009 0.4974 2.7709 sb1_ 0.5-1.0 1.2736 1.2808 6.006 mb_ 1.0-2.0 1.8664 1.8681 5.4819 hb_ 2.0-4.5 0.7266 0.7307 1.9276 fb_ 0.2-4.5 

This table was created by the HEASARC in July 2015 based on an electronic version of Table 3 of the reference paper, the list of XMM-Newton X-ray point sources detected in a deep 8-field mosaic of M33, which was obtained from the ApJS web site. This is a service provided by NASA HEASARC .