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Description
This table contains the results of a 20 ks XMM-Newton observation of the Lagoon Nebula (M 8). The EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very young open cluster NGC 6530. The bulk of these X-ray sources are probably associated with low and intermediate mass pre-main sequence stars. One of the sources experienced a flare-like increase of its X-ray flux making it the second brightest source in M 8 after the O4 star 9 Sgr. The X-ray spectra of most of the brightest sources can be fitted with thermal plasma models with temperatures of kT ~ a few keV. Only a few of the X-ray selected PMS candidates are known to display H-alpha emission and were previously classified as classical T Tauri stars. This suggests that most of the X-ray emitting PMS stars in NGC 6530 are weak-line T Tauri stars. In addition to 9 Sgr, the EPIC field of view contains also a few early-type stars. This table contains information on 117 of the 119 X-ray sources (2 sources, a point source associated with 9 Sgr and an extended source associated with the Hourglass Nebula were excluded from this table by the authors) that were detected using the SAS source detection algorithms in the soft band (0.5 - 1.2 keV) of an EPIC observation of 9 Sgr which have either a combined likelihood >= 20 and are detected in the individual images from all 3 EPIC instruments with -ln p_i >= 3.0 or (in two cases) where clearly detected in 2 of the 3 instruments but fell outside of the FOV of the third. The faintest sources in this category have about 10-3 cts s<sup>-1</sup> over the 0.5 - 1.2 keV band of the MOS instruments. Assuming a 1 keV thermal spectrum with a neutral hydrogen column density of 0.17 x 10<sup>22</sup> cm<sup>-2</sup>, the faintest sources correspond to an observed flux of about 8.9 x 10<sup>-15</sup> erg cm<sup>-2</sup> s<sup>-1</sup> and an unabsorbed flux of 13.1 x 10<sup>-15</sup> erg cm<sup>-2</sup> s<sup>-1</sup> in the 0.5 - 5.0 keV energy range. Note that the corresponding observed flux in the 0.5 - 1.2 keV soft band would be 5.2 x 10<sup>-15</sup> erg cm<sup>-2</sup> s<sup>-1</sup>. 72 X-ray sources have a single optical counterpart from the Sung et al (2000, <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/AJ/120/333">CDS Cat. <J/AJ/120/333></a>) catalog or in the SIMBAD database within a radius of less than 9 arcsec. The average angular separation between the X-ray source and the optical counterpart is 4.1 +/- 2.1 arcseconds. 17 X-ray sources have two or more optical stars falling within the 9 arcsec radius. Seven of these sources have at least one known H-alpha emission star inside their error box. 28 sources do not have an optical counterpart in the catalogue of Sung et al. The authors have cross-correlated these sources with the Guide Star Catalog and, in most cases, they find one or several GSC objects inside the 9 arcsec radius. These optical counterparts are usually very faint (V or R >=17) except for sources 91, 92 and 94 that have counterparts with R magnitudes 15.0, 14.6 and 13.3 respectively (note that these sources fall outside the area investigated by Sung et al.). Sources 93, 96, 98, 99, 100, 101, 102 and 112 have no GSC counterpart. Most of the objects in Table 3 are therefore X-ray sources with high X-ray to visual luminosity ratios. Given the galactic coordinates of NGC 6530 (l_II = 6.14, b_II = -1.38), the total galactic column density along this line of sight must be extremely large and the number of extragalactic sources in the soft detection energy band should be extremely low. This table was created by the HEASARC in March 2007 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/395/499">CDS catalog J/A+A/395/499</a> files table1.dat, table2.dat and table3.dat. This is a service provided by NASA HEASARC .
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