------------------------------------------------------------------------ IR_Xray_gcnews.tex ApJ, 2008, in press In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Virus-Scanned: ClamAV 0.93.3/8048/Fri Aug 15 08:56:27 2008 on mailserv.dmz.astronomy.osu.edu X-Virus-Status: Clean X-MailScanner-Information: Please contact the postmaster@aoc.nrao.edu for more information X-MailScanner-ID: m7FLQt8e006048 X-MailScanner: Found to be clean X-MailScanner-SpamCheck: not spam, SpamAssassin (not cached, score=0, required 5, autolearn=disabled) X-MailScanner-From: sellgren@astronomy.ohio-state.edu X-Spam-Status: No % astro-ph/0806.1880 \documentclass[12pt,preprint]{aastex} \begin{document} \title{Comparison of 3.6 -- 8.0 Micron {\it Spitzer}/IRAC Galactic Center Survey Point Sources with Chandra X--Ray Point Sources in the Central 40x40 Parsecs} \author{ {R.~G.~Arendt}\altaffilmark{1,2}, {D.~Y.~Gezari}\altaffilmark{3}, {K.~Sellgren}\altaffilmark{5}, {S.~V.~Ram\'{\i}rez}\altaffilmark{6}, {C.~J.~Law}\altaffilmark{7,8}, {H.~A.~Smith}\altaffilmark{9}, {S.~H.~Moseley}\altaffilmark{3} {CRESST/UMBC/GSFC; richard.g.arendt@nasa.gov} \altaffiltext{2} \altaffiltext{3} \altaffiltext{4} \altaffiltext{5} \altaffiltext{6} \altaffiltext{7} \altaffiltext{8} \altaffiltext{9} \altaffiltext{10} \begin{abstract} We have studied the correlation between 2357 Chandra X--ray point sources in a $40 \times 40$ parsec field and $\sim$20,000 infrared sources we observed in the corresponding subset of our $2\arcdeg \times 1.4\arcdeg$ {\it Spitzer}/IRAC Galactic Center Survey at 3.6--8.0 $\micron$, using various spatial and X--ray hardness thresholds. The correlation was determined for source separations of less than $0\farcs5$, 1$''$ or 2$''$. Only the soft X--ray sources show any correlation with infrared point sources on these scales, and that correlation is very weak. The upper limit on hard X--ray sources that have infrared counterparts is $<1.7\%$ (3$\sigma$). However, because of the confusion limit of the IR catalog, we only detect IR sources with absolute magnitudes $\lesssim 1$. As a result, a stronger correlation with fainter sources cannot be ruled out. Only one compact infrared source, IRS~13, coincides with any of the dozen prominent X--ray emission features in the $3 \times 3$ parsec region centered on Sgr A*, and the diffuse X--ray and infrared emission around Sgr A* seems to be anti-correlated on a few-arcsecond scale. We compare our results with previous identifications of near--infrared companions to Chandra X--ray sources. \end{abstract} \keywords{Galaxy: center --- infrared: stars --- X-rays: binaries} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \section{Introduction} X-ray surveys of the Galactic center with {\it Chandra X-Ray Observatory} (Wang et al.\ 2002; Muno et al.\ 2003) have provided a deep sampling of the population of X--ray point sources that shows a large increase in source density toward the Galactic Center. These X--ray sources have been modeled as a population mix of various sorts of X-ray binaries, Wolf-Rayet stars, nearby X-ray active stars in the foreground, and background AGN (Pfahl et al.\ 2002; Belczynski \& Taam 2004; Ebisawa et al.\ 2005; Ruiter et al.\ 2006; Liu \& Li 2006; Muno et al.\ 2006). However, the high extinction toward the Galactic center prohibits the detection of visible light emitted by the stellar components in the expected binaries. Near--IR searches have also had little success in detecting IR counterparts of the X--ray point sources. Several OB stars and Wolf-Rayet stars have been identified with X-ray sources by near-IR spectroscopy (Muno et al.\ 2006, Mikles et al.\ 2006, Mauerhan et al.\ 2007), but the paucity of near-IR detections sets limits that suggest only a small fraction of the X--ray sources can be high mass X--ray binaries (HMXBs; Laycock et al.\ 2005; Bandopadhyay et al.\ 2006). Our {\it Spitzer Space Telescope} IRAC survey of the Galactic Center (Stolovy et al.\ 2006, S. Stolovy et al.\ 2008 in preparation) provides a new opportunity to search for IR counterparts to the X--ray sources. IRAC observations cover four broad bands at 3.6, 4.5, 5.8 and 8 $\micron$. The survey imaged a $2.0\arcdeg \times 1.4\arcdeg$ ($280 \times 200$ parsec at 8.0 kpc) region of the Galactic Center with a nominal resolution of $\sim2''$ (Figure 1). Since our observations are at longer wavelengths than ground--based near--IR ($J, H, K$) observations, extinction should be less of a hinderance to the detection of stellar companions. Furthermore, at the longest IRAC wavelengths (5.8 and especially 8 $\micron$), IRAC is sensitive to circumstellar dust emission which may cause significant extinction at shorter wavelengths. Thus, comparison of the X--ray and IR point source catalogs may reveal stellar companions which are at an evolutionary stage where they produce large quantities of dust, or are simply too heavily attenuated by the line of sight extinction at shorter wavelengths. We calculated the correlation between 2357 hard and soft Chandra X--ray sources identified and catalogued by Muno et al.\ (2003) and the $\sim$20,000 {\it Spitzer}/IRAC infrared point sources that lie within a $40 \times 40$ parsec ($20 \times 20$ arcmin) field at the Galactic Center (Figure 2). The IR sources are a small subset of our full catalog (Ram\'irez et al.\ 2008) which has a mean confusion limit of $[3.6] = 12.4$ mag. We divide the Chandra sources by their hardness because the high column density of gas towards the GC, $N_H$ $\sim$ 5 $\times$ 10$^{22}$ cm$^{-2}$, absorbs all soft X-rays. Thus soft X-ray sources must be in the foreground towards the GC; hard X-ray sources can be at the 8 kpc distance of the GC or can be foreground/background sources. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \section{Analysis} \subsection{IR/X--ray Point Source Correlations} The positional uncertainty of the IRAC point sources is correlated with wavelength. In the final band--merged catalog, the reported position is that measured at the shortest IRAC wavelength at which each source was detected. Within a radius of $10'$ from the galactic center 86\% of the IRAC sources are detected at 3.6 or 4.5 $\micron$. According to Ram\'irez et al.\ (2008), 90\% of these sources have positional errors of $<0.16''$. The positional uncertainties of the X--ray sources are reported by Muno et al.\ (2003) to be increasing with distance from the center of the field. Based on the given information, we have assigned uncertainties to the X--ray positions that are the larger of $0\farcs3$ or $0.209''\ e^{\theta/225''}$, where $\theta$ is the distance from the center of the field. With this prescription, only 39 of the 2357 X--ray sources have positional uncertainties $>2\farcs5$, and 1645 ($\sim70\%$) have uncertainties $<0\farcs8$. In light of these positional uncertainties, we searched for infrared sources that fell within three different limits ($0\farcs5$, 1$''$ and 2$''$) of the Muno et al.\ (2003) X--ray source positions. The tightest constraint here ($0\farcs5$), should include all associations between infrared and X--ray sources with high positional accuracies. Some associations between sources with larger positional errors may be missed, but the tight limit will best exclude coincidental associations between unrelated sources along the same line of sight. The looser limits were employed to provide a more complete census of the total number of possible associations, and to provide a statistical test for random unrelated associations, which should increase directly proportionally to the area of the constraint. Figures \ref{fig_ch1x}a and \ref{fig_ch4x}a show all the X--ray source locations plotted on the IRAC 3.6 and 8 $\micron$ images. Figures \ref{fig_ch1x}b and \ref{fig_ch4x}b show only the X--ray sources with IR counterparts within the specified limits ($<2''$, 1$''$, $0\farcs5$ are red, green and blue symbols respectively). Figure \ref{fig_dots}a--b illustrates the cataloged distribution of IR sources and X--ray sources. The distribution of IR sources appears uniform only because it is confusion limited. For stars much brighter than the confusion limit, the density is peaked at the Galactic center (Ram\'irez et al.\ 2008) as is that of the X--ray sources. The number of X--ray sources $N$ found coincident with an IR source, for each of the three radial constraints and at each IRAC wavelength is listed in Table 1. The statistical uncertainty on $N$ is given by $\sigma_N = \sqrt{N}$. The X--ray and infrared sources in the study field show an extremely weak correlation. Fewer than 7\% of the 2357 X--ray sources had 3.6 $\micron$ counterparts in the catalog of IRAC infrared sources in a 1$''$ sampling radius, and most of these are likely to be false identifications. The number of counterparts decreases with increasing wavelength. \subsection{Likelihood of Chance Associations} We determined the likelihood of false correlations in the crowded infrared field by repeating the same correlation analysis eight additional times, but with the X--ray source position template offset from the nominal location, in a $5''$--pitch regular grid of eight positions N--S and E--W of center. Figure \ref{fig_dots}c shows the distribution of the X--ray sources with 3.6 $\micron$ counterparts (within 1$''$), and Figure \ref{fig_dots}d shows the distribution when the IR sources are artificially offset by 5$''$. The mean number of X--ray sources with IR counterparts in these offset comparisons is listed in Table 1 as $M$, with $\sigma_M = \sqrt{M/8}$. The number of coincidences found in excess of chance is $N-M$. This excess is typically 1\% of the X--ray sources, and never larger than 3 times the statistical uncertainty. However, the fact that $M$ increases proportionally to the area of the matching constraint, while $N$ increases more slowly, is another indication that (depending on wavelength) roughly 10-30 of the matching IR and X--ray sources are real associations. There are no cases of multiple candidates within circles of $0\farcs5$ or 1$''$, and only 11 sources with 2 candidates within a 2$''$ circle. These numbers are lower than expected by random chance because the width of the IRAC beam prevents resolving sources that are closer together than $\sim3''$. As some of the X--ray sources do have fairly large positional uncertainties, we have repeated the matching using only the X--ray sources with uncertainties $<0\farcs8$. These results are shown in Table 2. Qualitatively, the results are similar to Table 1, in that the offset matching tests usually find fewer matches than the properly aligned tests. Also the number of matching sources ($N$) again rises more slowly than is expected (and measured by $M$) for purely random associations. However, because the overall sample size is reduced by a factor of 0.7, the results are not as statistically significant as those obtained using the full sample. An interesting difference appears if we separate the X--ray sources according to their spectral hardness. There is a modest excess in the number of soft X--ray sources (defined as those with detections in the 0.5--2.0 keV band) with infrared counterparts above that expected from random chance (Table 3). There is a 4$\sigma$ excess in the number of soft X--ray sources with IR counterparts at 3.6 $\micron$ compared to a 2$\sigma$ excess in the correlations at 8.0 $\micron$. Again the trend persists, but with lower statistical significance, if we limit the X--ray data set to those sources with positional uncertainties $<0\farcs8$ (Table 4). Based on the soft X--rays observed from these sources (and therefore their relatively low column densities), we expect that the soft X--ray sources are foreground objects, and not at the distance of the Galactic Center. The excess soft X--ray/IR correlation is therefore likely due to these sources being nearby, rather than being intrinsically bright in both wavebands. In contrast, the hard X--ray sources seem to have only as many infrared counterparts as would be expected from random associations (Tables 5 and 6). This is indicated both by the comparison of the aligned and offset matching ($N$ vs. $M$), and by the way $N$ increases proportionally to the area of the matching constraint. \section{Results} We provide a listing of IR and X--ray sources coincident within 1$''$ in Table 7. The table is provided to facilitate follow up research on these sources, but we remind the reader that the majority of these associations are likely to be merely coincidental. The table contains designations and coordinates from each catalog, along with the IR magnitudes, an indication X--ray spectral hardness, and the actual separation between the associated sources. Much additional information can be found by consulting the original catalogs (Muno et al.\ 2003; Ram\'irez et al.\ 2008). \subsection{Nature of the Correlations} The spatial distribution of soft X--ray sources is less concentrated toward the Galactic Center than that of the hard sources. Figure \ref{fig_cumul} shows the cumulative distributions of distance from Sgr A* for all X--ray sources and for the hard and soft sources separately. Also shown is the distribution of the 51 sources which had 3.6 $\micron$ IR counterparts within $0\farcs5$. These distributions can be compared statistically using the Kolmogorov--Smirnov (K--S) test (e.g.\ Press et al.\ 1986). This test measures the maximum separation $D$ between two cumulative distributions. Then we calculate that probability of having the two distributions differ by $D$ or larger, under the assumption that they are sampled from the same parent distribution. By this statistic, the probability of finding the observed $D(hard-soft)$ is essentially 0, if the two types of X--ray source really have the same radial spatial distribution with respect to Sgr A*. The probability of finding the observed $D(hard - 3.6\micron)$ is 0.01, and the probability of finding the observed $D(soft - 3.6\micron)$ is 0.72. Thus, the K-S test indicates that it is statistically unlikely that the hard X--ray sources and the set of matching 3.6 $\micron$ IR sources share the same degree of clustering toward the Galactic Center. Whereas the distribution of the matching 3.6 $\micron$ IR associations is entirely consistent with that of the soft X--ray sources. This is further evidence that a substantial majority of IR counterparts are associated with the soft X--ray sources rather than the more numerous hard sources. For comparison the distribution of all 3.6 $\micron$ sources within the same area of the X-ray sources is also shown in Figure \ref{fig_cumul}. As would be inferred from Figure \ref{fig_dots}a, this distribution is very close to (but not exactly) uniform. The probability of finding $D(uniform - all\ 3.6\micron)$ is 0.03. \subsection{Infrared Colors of Counterparts to X--ray Sources} We next investigated the colors of the potential IR counterparts, to see if they might be useful for separating intrinsic IR/X--ray sources from the random associations. The color--magnitude diagram for the 17613 IRAC sources in the $40 \times 40$ parsec study region that were detected at both 3.6 and 4.5 $\micron$ is shown in Figure \ref{fig_cmd}. The circles and squares indicate IR stars that are identified with hard and soft X--ray sources, respectively, in the Muno et al.\ (2003) catalog. 42 X--ray sources had IRAC sources falling within $0\farcs5$ of the nominal X--ray positions (large circles/squares), 130 had IRAC sources within 1$''$ (medium circles/squares), and 394 had IRAC sources falling within 2$''$ (small circles/squares). See Tables 1--3 for details, including statistics for hard and soft X--ray sources. The colors of the possible infrared counterparts do not seem to be unusual in any way. The distribution of colors of those infrared stars that have coincident X--ray sources is essentially the same as the distribution of all other infrared stars in our sample. There is also no apparent differentiation between the colors of infrared stars as a function of their distance from the X--ray source. The K-S test reveals no significant difference between the color distributions of the infrared candidates and the larger sample of all infrared sources within the field. Thus, the observed colors of the IRAC point sources are of little use in attempting to discriminate between real and coincidental X--ray/IR correlations. \subsection{Infrared and X--ray Sources at the Central Parsec} Casual inspection of the Chandra and {\it Spitzer}/IRAC images gives the impression that the bright X--ray cluster at the Galactic Center is well-correlated with the infrared emission. However, closer examination shows that only one of the bright, compact mid-infrared sources, IRS 13, coincides with any of the discrete X-ray sources in the central 3 $\times$ 3 parsecs (Figure \ref{fig_zoom}). The separation between the X--ray and IRAC positions is $<1''$ (see source SSTGC 0524504 in Table 7). Notably, IRS 13 has been proposed as a candidate host for an intermediate black hole (Maillard et al.\ 2004). While we do also detect IRS 10* (= IRS 10EE), the mid-infrared counterpart to an SiO maser source, with Spitzer/IRAC, and Peeples et al.\ (2007) identify a Chandra X-ray source with IRS 10*, that X-ray source is more than 2$''$ east of IRS 10* so it does not meet our correlation criteria. Peeples et al.\ (2007) find spatial coincidences between Chandra X-ray sources and five other point sources they observe at 1.6 and 2.2 $\micron$, but we do not detect any of these sources with $Spitzer$/IRAC. Thus, with the exception of IRS 13, none of the point sources in the central 3 $\times$ 3 parsecs imaged in the $Spitzer$/IRAC 3.6 -- 8.0 $\micron$ survey, and none of the compact 12 $\micron$ IRS sources imaged with sub-arcsec resolution by Gezari et al.\ (1996), have X-ray counterparts. The X--ray emission in the immediate vicinity of Sgr A* is discussed in Gezari et al.\ (2006). %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \section{Discussion} Several population studies have been done to estimate what the relative contributions of different X-ray sources are to the Galactic Center catalog of Muno et al.\ (2003) or other Galactic Center X-ray surveys. These models give insight into what infrared counterparts we might hope to find with Spitzer/IRAC. The Galactic Center is thought to contain a mix of CVs, magnetically accreting CVs (intermediate polars), low-mass X-ray binaries (LMXBs), high-mass X-ray binaries (HMXBs), massive stars with strong winds, colliding wind binaries, and pulsars (Pfahl et al.\ 2002; Belczynski \& Taam 2004; Ruiter et al.\ 2006; Liu \& Li 2006; Muno et al.\ 2006). We would like to know which of these are most likely to be detectable at a distance of 8 kpc with Spitzer/IRAC. The donor stars for HMXBs, massive stars with strong winds, and colliding wind binaries are O stars and Wolf-Rayet stars. These stars are luminous enough to be detected with Spitzer/IRAC, especially if they have circumstellar dust or heat the surrounding interstellar medium. The donor stars for CVs, intermediate polars, and LMXBs are probably not luminous enough to be detected with Spitzer/IRAC unless they are a red giant or they are surrounded by circumstellar dust. The INTEGRAL gamma--ray observatory has discovered a new class of hard X--ray source in the Galactic plane: highly obscured HMXBs, with hydrogen column densities much higher than predicted by their extinction, due to intrinsic absorption in the wind of the supergiant secondary (Dean et al.\ 2005; Walter et al.\ 2006). {\it Spitzer}/IRAC photometry of highly obscured supergiant HMXBs has detected moderate infrared excesses from a hot dust component, but with roughly a 25\% success rate (Kaplan et al.\ 2006; Rahoui et al.\ 2008). However, none of these cases show evidence for a large mass of cooler dust in the systems, which could lead to a rising mid-IR spectrum at wavelengths $\gtrsim 5\micron$. Our lack of detection of a large number of 8 $\micron$ counterparts suggests that the GC X-ray sources also lack massive dusty shells. Pfahl et al.\ (2002) conclude that most of the X-ray sources found by Wang et al.\ (2002), in a wider but shallower Chandra survey of the Galactic Center, are HMXBs: neutron stars with O or B star companions. Other authors, however, conclude that only a small fraction of the Muno et al.\ (2003) Galactic Center X-ray sources are associated with massive stars (Belczynski \& Taam 2004; Ruiter et al.\ 2006; Liu \& Li 2006; Muno et al.\ 2006). Muno et al.\ (2006), Mikles et al.\ (2006), and Mauerhan et al.\ (2007) have combined Chandra point source catalogs of the Galactic Center with the 2MASS catalog to find candidate massive stars. Muno et al.\ (2006) also includes 3.6 cm radio data. They discard all soft X-ray sources, because the interstellar absorption to the Galactic Center will absorb all soft X-ray emission from there. They also discard all 2MASS sources with blue J-K colors as being foreground sources, because the interstellar extinction to the Galactic Center reddens all sources there. They use near-IR spectra to identify three (Muno et al.\ 2006), one (Mikles et al.\ 2006), and two (Mauerhan et al.\ 2007) massive stars in the Galactic Center with X-ray emission. That so much effort has gone into identifying a total of six massive stars with X-ray emission, either from colliding winds or from accretion onto a compact companion, out of more than a thousand hard X-ray sources in the Galactic Center, underscores the difficulty of observing infrared emission from the donor stars for X-ray sources in the Galactic Center. Bandyopadhyay et al.\ (2005), reported that roughly 75\% of a sample of 77 hard X--ray sources had faint ($K = 13 - 20$) candidate K--band counterparts within a $1\farcs3$ radius. However, they noted that this is exactly the number of random associations that they predict from a Monte Carlo simulation. Thus although Bandyopadhyay et al.\ (2005) identified 58 K--band ``candidates'' none of these sources are likely to be real infrared counterparts to the hard X--ray sources in their sample. Correlations at H and J bands did show small statistical excess above the randomly expected number of associations. Follow--up spectroscopic observations by Bandyopadhyay et al.\ (2006) failed to find indications of accretion (e.g.\ Br $\gamma$ emission) among 28 candidates observed. They conclude that the apparent associations are merely foreground stars, and that the X--ray sources are likely dominated by a population of low mass X--ray binaries (LMXBs) and cataclysmic variables (CVs) with $K > 20$. Laycock et al.\ (2005) compared 1453 hard and 105 soft X--ray sources with near infrared stars from the 2MASS survey and concluded that high--mass X--ray binaries are not the dominant hard X--ray source population. Unlike the hard X--ray sources examined by Bandyopadhyay et al.\ (2006), we clearly do detect (if only in a statistical sense) a population of sources with both soft X--ray and infrared emission, notably in the 3.6 and 4.5 $\micron$ bands (a net excess of $\sim34\pm8$ sources in these bands when a positional agreement of $< 1''$ is required; see Table 3). These sources represent $\sim6\%$ of the complete soft X--ray sample and, as noted previously, are likely foreground sources rather than being intrinsically bright in IR and X--rays. Ebisawa et al.\ (2005) observed a blank part of the galactic plane with Chandra, and were able to find 2MASS identifications for almost all their soft X-ray sources; they concluded they were nearby active stars on the main sequence. For comparison, Sidoli et al.\ (2001) found 107 sources in a 12 deg$^2$ region around the GC surveyed with the ROSAT PSPC, which was sensitive to X--rays between 0.1--2.4 keV. Of these 107, they identified 20 (or 19\%) as being associated with stars, noting that these have softer or less absorbed spectra. Although our data cannot conclusively determine if the softer X--ray sources with IR counterparts are indeed from a different population than the sources without counterparts, this could be tested with more observations and may represent a method to eliminate foreground sources from a GC catalog. The donor stars in both LMXBs and CVs at the GC are expected to be too faint to be detected in our IRAC survey. Over the full IRAC GC survey, Ram\'irez et al.\ (2008) set mean confusion limits at 12.4, 12.1, 11.7 and 11.2 mag for 3.6, 4.5, 5.8 and 8 $\micron$ respectively. However, because of the general increase in the volume density of stars with decreasing distance from the Galactic Center, confusion limits are about 2 magnitudes brighter in the vicinity of Sgr A (see Fig. 8 of Ram\'irez et al.\ 2008). Given a distance modulus of 7.26 and extinction of about 1.5 - 2 magnitudes, scaled from $A_K \approx 3.3$ (Blum et al.\ 1996), using either the Indebetouw et al.\ (2005) or Flaherty et al.\ (2007) extinction laws, we should only detect sources with absolute magnitudes $\lesssim 1$. Variations in extinction across the region may alter the apparent magnitudes of some IR sources, but the main limitation of the IRAC survey is due to confusion, not extinction nor sensitivity. At 8 $\micron$ and to a lesser degree at 5.8 $\micron$, a large instrumental beam, and confusion from the diffuse ISM are additional limitations which reduce the number of sources detected compared to 3.6 and 4.5 $\micron$. While the extinction is not the dominant factor in the detection of the IR sources, it is interesting to note that extinction appears to have a strong effect on the distribution of the X--ray sources. In Figures \ref{fig_ch1x}a and \ref{fig_ch4x}a, there is an evident correlation between a relatively low X--ray source density and an IR dark cloud (IRDC) to the southeast of the Galactic Center. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \section{Conclusions} We have analyzed the possible correlations between the largest number of candidate sources to date: 2357 X--ray sources (of which 1809 are hard X--ray sources most likely located at the Galactic Center) and $\sim$20,000 {\it Spitzer}/IRAC infrared point sources. Source confusion limits our correlations to only bright infrared sources with absolute magnitudes $\lesssim 1$ if located near the Galactic Center. The lack of any significant correlation between hard X--ray sources and 3.6 -- 8 $\micron$ infrared point sources suggests that there is no unique population of sources that are bright at both X--ray and 3.6 -- 8 $\micron$ wavelengths. Based on this study, we can set the upper limit on the fraction of all hard X--ray sources that can be bright at both X--ray and 3.6 -- 8 $\micron$ wavelengths to be $<1.7\%$ (3$\sigma$). \acknowledgements This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA. KS thanks the NASA Faculty Fellowship Program for financial support and the hospitality of JPL's Long Wavelength Center and the Spitzer Science Center. We thank the referee for substantial comments and suggestions. \begin{thebibliography}{} \bibitem[Bandyopadhyay2005]{329} Bandyopadhyay, R. 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Series, 54, 176 \bibitem[Walter et al.(2006)]{2006A&A...453..133W} Walter, R., et al.\ 2006, \aap, 453, 133 \bibitem[Wang et al.(2002)]{2002Natur.415..148W} Wang, Q.~D., Gotthelf, E.~V., \& Lang, C.~C.\ 2002, \nat, 415, 148 \end{thebibliography} \clearpage \begin{deluxetable}{lccccccc} \tabletypesize{\scriptsize} \tablewidth{0pt} \tablecaption{All X-ray Sources (2357)} \tablehead{ \colhead{Wavelength ($\micron$)} & \colhead{$N$} & \colhead{$\sigma_N$} & \colhead{$M$} & \colhead{$\sigma_M$} & \colhead{$N-M$} & \colhead{$\sigma_{N-M}$} & \colhead{$(N-M)/\sigma_{N-M}$} } \startdata \cutinhead{Positional agreement $< 0.5''$} 3.6 & 51 & 7.1 & 30.5 & 2.0 & 20.5 & 7.4 & 2.8\\ 4.5 & 46 & 6.8 & 27.8 & 1.9 & 18.2 & 7.0 & 2.6\\ 5.8 & 35 & 5.9 & 19.9 & 1.6 & 15.1 & 6.1 & 2.5\\ 8 & 22 & 4.7 & 10.1 & 1.1 & 11.9 & 4.8 & 2.5\\ \cutinhead{Positional agreement $< 1.0''$} 3.6 & 156 & 12.5 & 120.4 & 3.9 & 35.6 & 13.1 & 2.7\\ 4.5 & 137 & 11.7 & 108.2 & 3.7 & 28.8 & 12.3 & 2.3\\ 5.8 & 104 & 10.2 & 77.4 & 3.1 & 26.6 & 10.7 & 2.5\\ 8 & 64 & 8.0 & 42.0 & 2.3 & 22.0 & 8.3 & 2.6\\ \cutinhead{Positional agreement $< 2.0''$} 3.6 & 488 & 22.1 & 458.4 & 7.6 & 29.6 & 23.4 & 1.3\\ 4.5 & 424 & 20.6 & 414.5 & 7.2 & 9.5 & 21.8 & 0.4\\ 5.8 & 320 & 17.9 & 297.9 & 6.1 & 22.1 & 18.9 & 1.2\\ 8 & 179 & 13.4 & 170.9 & 4.6 & 8.1 & 14.2 & 0.6\\ \enddata \end{deluxetable} \begin{deluxetable}{lccccccc} \tabletypesize{\scriptsize} \tablewidth{0pt} \tablecaption{All X-ray Sources with Uncertainty $<\ 0\farcs8$ (1645)} \tablehead{ \colhead{Wavelength ($\micron$)} & \colhead{$N$} & \colhead{$\sigma_N$} & \colhead{$M$} & \colhead{$\sigma_M$} & \colhead{$N-M$} & \colhead{$\sigma_{N-M}$} & \colhead{$(N-M)/\sigma_{N-M}$} } \startdata \cutinhead{Positional agreement $< 0.5''$} 3.6 & 29 & 5.4 & 20.5 & 1.6 & 8.5 & 5.6 & 1.5\\ 4.5 & 27 & 5.2 & 18.2 & 1.5 & 8.8 & 5.4 & 1.6\\ 5.8 & 19 & 4.4 & 13.0 & 1.3 & 6.0 & 4.5 & 1.3\\ 8.0 & 11 & 3.3 & 6.2 & 0.9 & 4.8 & 3.4 & 1.4\\ \cutinhead{Positional agreement $< 1.0''$} 3.6 & 97 & 9.8 & 86.0 & 3.3 & 11.0 & 10.4 & 1.1\\ 4.5 & 86 & 9.3 & 75.8 & 3.1 & 10.2 & 9.8 & 1.0\\ 5.8 & 66 & 8.1 & 55.5 & 2.6 & 10.5 & 8.5 & 1.2\\ 8.0 & 37 & 6.1 & 29.4 & 1.9 & 7.6 & 6.4 & 1.2\\ \cutinhead{Positional agreement $< 2.0''$} 3.6 & 328 & 18.1 & 324.9 & 6.4 & 3.1 & 19.2 & 0.2\\ 4.5 & 272 & 16.5 & 290.9 & 6.0 & -18.9 & 17.6 & -1.1\\ 5.8 & 213 & 14.6 & 210.4 & 5.1 & 2.6 & 15.5 & 0.2\\ 8.0 & 121 & 11.0 & 118.6 & 3.9 & 2.4 & 11.7 & 0.2\\ \enddata \end{deluxetable} \begin{deluxetable}{lccccccc} \tabletypesize{\scriptsize} \tablewidth{0pt} \tablecaption{Soft X-ray Sources (548)} \tablehead{ \colhead{Wavelength ($\micron$)} & \colhead{$N$} & \colhead{$\sigma_N$} & \colhead{$M$} & \colhead{$\sigma_M$} & \colhead{$N-M$} & \colhead{$\sigma_{N-M}$} & \colhead{$(N-M)/\sigma_{N-M}$} } \startdata \cutinhead{Positional agreement $< 0.5''$} 3.6 & 28 & 5.3 & 5.8 & 0.8 & 22.2 & 5.4 & 4.2\\ 4.8 & 23 & 4.8 & 5.1 & 0.8 & 17.9 & 4.9 & 3.7\\ 5.8 & 17 & 4.1 & 3.5 & 0.7 & 13.5 & 4.2 & 3.2\\ 8 & 8 & 2.8 & 1.5 & 0.4 & 6.5 & 2.9 & 2.3\\ \cutinhead{Positional agreement $< 1.0''$} 3.6 & 64 & 8.0 & 26.4 & 1.8 & 37.6 & 8.2 & 4.6\\ 4.5 & 55 & 7.4 & 24.1 & 1.7 & 30.9 & 7.6 & 4.1\\ 5.8 & 37 & 6.1 & 15.9 & 1.4 & 21.1 & 6.2 & 3.4\\ 8 & 20 & 4.5 & 7.2 & 1.0 & 12.8 & 4.6 & 2.8\\ \cutinhead{Positional agreement $< 2.0''$} 3.6 & 126 & 11.2 & 103.0 & 3.6 & 23.0 & 11.8 & 2.0\\ 4.5 & 109 & 10.4 & 95.1 & 3.4 & 13.9 & 11.0 & 1.3\\ 5.8 & 78 & 8.8 & 69.2 & 2.9 & 8.8 & 9.3 & 0.9\\ 8 & 42 & 6.5 & 37.4 & 2.2 & 4.6 & 6.8 & 0.7\\ \enddata \end{deluxetable} \begin{deluxetable}{lccccccc} \tabletypesize{\scriptsize} \tablewidth{0pt} \tablecaption{Soft X-ray Sources with Uncertainty $<\ 0\farcs8$ (303)} \tablehead{ \colhead{Wavelength ($\micron$)} & \colhead{$N$} & \colhead{$\sigma_N$} & \colhead{$M$} & \colhead{$\sigma_M$} & \colhead{$N-M$} & \colhead{$\sigma_{N-M}$} & \colhead{$(N-M)/\sigma_{N-M}$} } \startdata \cutinhead{Positional agreement $< 0.5''$} 3.6 & 16 & 4.0 & 3.2 & 0.6 & 12.8 & 4.1 & 3.1\\ 4.5 & 14 & 3.7 & 2.9 & 0.6 & 11.1 & 3.8 & 2.9\\ 5.8 & 9 & 3.0 & 1.6 & 0.5 & 7.4 & 3.0 & 2.4\\ 8.0 & 3 & 1.7 & 0.9 & 0.3 & 2.1 & 1.8 & 1.2\\ \cutinhead{Positional agreement $< 1.0''$} 3.6 & 34 & 5.8 & 15.4 & 1.4 & 18.6 & 6.0 & 3.1\\ 4.5 & 30 & 5.5 & 13.9 & 1.3 & 16.1 & 5.6 & 2.9\\ 5.8 & 19 & 4.4 & 8.6 & 1.0 & 10.4 & 4.5 & 2.3\\ 8.0 & 9 & 3.0 & 4.2 & 0.7 & 4.8 & 3.1 & 1.5\\ \cutinhead{Positional agreement $< 2.0''$} 3.6 & 68 & 8.2 & 58.4 & 2.7 & 9.6 & 8.7 & 1.1\\ 4.5 & 57 & 7.5 & 54.0 & 2.6 & 3.0 & 8.0 & 0.4\\ 5.8 & 40 & 6.3 & 37.4 & 2.2 & 2.6 & 6.7 & 0.4\\ 8.0 & 21 & 4.6 & 21.0 & 1.6 & 0.0 & 4.9 & 0.0\\ \enddata \end{deluxetable} \begin{deluxetable}{lccccccc} \tabletypesize{\scriptsize} \tablewidth{0pt} \tablecaption{Hard X-ray Sources (1809)} \tablehead{ \colhead{Wavelength ($\micron$)} & \colhead{$N$} & \colhead{$\sigma_N$} & \colhead{$M$} & \colhead{$\sigma_M$} & \colhead{$N-M$} & \colhead{$\sigma_{N-M}$} & \colhead{$(N-M)/\sigma_{N-M}$} } \startdata \cutinhead{Positional agreement $< 0.5''$} 3.6 & 23 & 4.8 & 24.8 & 1.8 & -1.8 & 5.1 & -0.3\\ 4.5 & 23 & 4.8 & 22.6 & 1.7 & 0.4 & 5.1 & 0.1\\ 5.8 & 18 & 4.2 & 16.4 & 1.4 & 1.6 & 4.5 & 0.4\\ 8 & 14 & 3.7 & 8.6 & 1.0 & 5.4 & 3.9 & 1.4\\ \cutinhead{Positional agreement $< 1.0''$} 3.6 & 92 & 9.6 & 94.0 & 3.4 & -2.0 & 10.2 & -0.2\\ 4.5 & 82 & 9.1 & 84.1 & 3.2 & -2.1 & 9.6 & -0.2\\ 5.8 & 67 & 8.2 & 61.5 & 2.8 & 5.5 & 8.6 & 0.6\\ 8 & 44 & 6.6 & 34.8 & 2.1 & 9.2 & 7.0 & 1.3\\ \cutinhead{Positional agreement $< 2.0''$} 3.6 & 362 & 19.0 & 355.4 & 6.7 & 6.6 & 20.2 & 0.3\\ 4.5 & 315 & 17.7 & 319.4 & 6.3 & -4.4 & 18.8 & -0.2\\ 5.8 & 242 & 15.6 & 228.6 & 5.3 & 13.4 & 16.4 & 0.8\\ 8 & 137 & 11.7 & 133.5 & 4.1 & 3.5 & 12.4 & 0.3\\ \enddata \end{deluxetable} \begin{deluxetable}{lccccccc} \tabletypesize{\scriptsize} \tablewidth{0pt} \tablecaption{Hard X-ray Sources with Uncertainty $<\ 0\farcs8$ (1342)} \tablehead{ \colhead{Wavelength ($\micron$)} & \colhead{$N$} & \colhead{$\sigma_N$} & \colhead{$M$} & \colhead{$\sigma_M$} & \colhead{$N-M$} & \colhead{$\sigma_{N-M}$} & \colhead{$(N-M)/\sigma_{N-M}$} } \startdata \cutinhead{Positional agreement $< 0.5''$} 3.6 & 13 & 3.6 & 17.2 & 1.5 & -4.2 & 3.9 & -1.1\\ 4.5 & 13 & 3.6 & 15.4 & 1.4 & -2.4 & 3.9 & -0.6\\ 5.8 & 10 & 3.2 & 11.4 & 1.2 & -1.4 & 3.4 & -0.4\\ 8.0 & 8 & 2.8 & 5.4 & 0.8 & 2.6 & 2.9 & 0.9\\ \cutinhead{Positional agreement $< 1.0''$} 3.6 & 63 & 7.9 & 70.6 & 3.0 & -7.6 & 8.5 & -0.9\\ 4.5 & 56 & 7.5 & 61.9 & 2.8 & -5.9 & 8.0 & -0.7\\ 5.8 & 47 & 6.9 & 46.9 & 2.4 & 0.1 & 7.3 & 0.0\\ 8.0 & 28 & 5.3 & 25.1 & 1.8 & 2.9 & 5.6 & 0.5\\ \cutinhead{Positional agreement $< 2.0''$} 3.6 & 260 & 16.1 & 266.5 & 5.8 & -6.5 & 17.1 & -0.4\\ 4.5 & 215 & 14.7 & 236.9 & 5.4 & -21.9 & 15.6 & -1.4\\ 5.8 & 173 & 13.2 & 173.0 & 4.7 & 0.0 & 14.0 & 0.0\\ 8.0 & 100 & 10.0 & 97.6 & 3.5 & 2.4 & 10.6 & 0.2\\ \enddata \end{deluxetable} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{deluxetable}{lllccccclllcl} \rotate \tabletypesize{\scriptsize} \tablewidth{0pt} \tablecaption{IR and X--Ray Sources Coinciding within $1''$ (No Physical Association Implied)} \tablehead{ \multicolumn{7}{c}{IR Sources (Ram\'irez at al. 2008)} & & \multicolumn{4}{c}{X--Ray Sources (Muno et al.\ 2003)}\\ \cline{1-7}\cline{9-12} \colhead{Name} & \colhead{R.A. (deg)} & \colhead{Dec. (deg)} & \colhead{[3.6]} & \colhead{[4.5]} & \colhead{[5.8]} & \colhead{[8.0]} & \colhead{}& \colhead{Name} & \colhead{R.A. (deg) } & \colhead{Dec. (deg)} & \colhead{Spectrum\tablenotemark{a}} & \colhead{$\Delta$ ($''$)\tablenotemark{b}} } \startdata SSTGC 0469964 & 266.33191 & -29.02930 & 11.54 & 11.59 & \nodata & \nodata & & CXOGCJ174519.7-290146 & 266.33212 & -29.02947 & soft & 0.91 \\ SSTGC 0470990 & 266.33348 & -29.04629 & 11.15 & \nodata & \nodata & \nodata & & CXOGCJ174520.0-290246 & 266.33374 & -29.04620 & hard & 0.87 \\ SSTGC 0473500 & 266.33735 & -29.03927 & 8.91 & 8.17 & \nodata & \nodata & & CXOGCJ174521.0-290221 & 266.33755 & -29.03930 & hard & 0.64 \\ SSTGC 0476142 & 266.34154 & -28.99323 & 9.85 & 9.68 & \nodata & \nodata & & CXOGCJ174521.9-285936 & 266.34134 & -28.99344 & hard & 0.99 \\ SSTGC 0476234 & 266.34169 & -29.00903 & 9.42 & 8.95 & 8.30 & \nodata & & CXOGCJ174521.9-290032 & 266.34159 & -29.00908 & soft & 0.36 \\ SSTGC 0477415 & 266.34345 & -29.01875 & 9.28 & 9.21 & 8.77 & 8.55 & & CXOGCJ174522.4-290107 & 266.34369 & -29.01881 & hard & 0.79 \\ SSTGC 0479734 & 266.34707 & -28.95763 & 9.43 & 9.33 & 8.90 & \nodata & & CXOGCJ174523.2-285727 & 266.34682 & -28.95750 & soft & 0.92 \\ SSTGC 0479445 & 266.34664 & -29.01752 & 10.12 & 9.34 & 9.28 & 9.41 & & CXOGCJ174523.2-290103 & 266.34684 & -29.01764 & hard & 0.77 \\ SSTGC 0481996 & 266.35058 & -28.97954 & 9.93 & 9.51 & 9.21 & 9.32 & & CXOGCJ174524.1-285845 & 266.35064 & -28.97932 & soft & 0.82 \\ SSTGC 0482409 & 266.35126 & -29.03542 & 10.02 & 9.90 & 9.44 & \nodata & & CXOGCJ174524.3-290208 & 266.35145 & -29.03561 & soft & 0.91 \\ SSTGC 0483850 & 266.35344 & -29.00869 & 10.44 & \nodata & \nodata & \nodata & & CXOGCJ174524.7-290031 & 266.35326 & -29.00888 & hard & 0.89 \\ SSTGC 0484205 & 266.35400 & -29.04215 & 9.62 & 9.57 & 9.28 & \nodata & & CXOGCJ174525.0-290232 & 266.35419 & -29.04226 & hard & 0.71 \\ SSTGC 0485202 & 266.35557 & -29.02035 & 11.64 & 11.09 & \nodata & \nodata & & CXOGCJ174525.2-290113 & 266.35539 & -29.02049 & hard & 0.75 \\ SSTGC 0487698 & 266.35948 & -28.99733 & 8.92 & 8.10 & 7.59 & 7.51 & & CXOGCJ174526.3-285949 & 266.35961 & -28.99721 & hard & 0.60 \\ SSTGC 0492659 & 266.36710 & -28.99540 & \nodata & \nodata & \nodata & 9.23 & & CXOGCJ174528.0-285943 & 266.36702 & -28.99547 & hard & 0.36 \\ SSTGC 0492380 & 266.36669 & -29.00646 & 10.18 & 9.96 & \nodata & \nodata & & CXOGCJ174528.0-290023 & 266.36680 & -29.00644 & soft & 0.36 \\ SSTGC 0493525 & 266.36850 & -29.05255 & 11.22 & 10.93 & \nodata & \nodata & & CXOGCJ174528.4-290308 & 266.36841 & -29.05230 & hard & 0.93 \\ SSTGC 0494379 & 266.36984 & -28.99134 & 10.28 & \nodata & 9.88 & \nodata & & CXOGCJ174528.7-285928 & 266.36960 & -28.99120 & hard & 0.91 \\ SSTGC 0494207 & 266.36958 & -29.01202 & 9.74 & 9.65 & 9.07 & 8.93 & & CXOGCJ174528.7-290042 & 266.36979 & -29.01183 & hard & 0.96 \\ SSTGC 0494633 & 266.37021 & -28.95736 & 10.68 & 10.21 & 10.10 & \nodata & & CXOGCJ174528.8-285726 & 266.37030 & -28.95749 & soft & 0.55 \\ SSTGC 0495190 & 266.37111 & -29.06847 & 6.41 & 5.81 & 5.19 & 5.36 & & CXOGCJ174529.0-290406 & 266.37109 & -29.06846 & hard & 0.08 \\ SSTGC 0496104 & 266.37251 & -29.00714 & 11.67 & 11.38 & \nodata & \nodata & & CXOGCJ174529.4-290025 & 266.37254 & -29.00699 & hard & 0.56 \\ SSTGC 0496570 & 266.37324 & -29.03733 & 9.47 & 9.42 & \nodata & \nodata & & CXOGCJ174529.5-290215 & 266.37326 & -29.03754 & soft & 0.75 \\ SSTGC 0496855 & 266.37365 & -28.95047 & 11.79 & \nodata & \nodata & \nodata & & CXOGCJ174529.6-285701 & 266.37370 & -28.95046 & hard & 0.16 \\ SSTGC 0496842 & 266.37363 & -28.97793 & 10.30 & 9.69 & 9.50 & \nodata & & CXOGCJ174529.6-285840 & 266.37370 & -28.97790 & hard & 0.25 \\ SSTGC 0496808 & 266.37358 & -29.00602 & 10.78 & 10.42 & \nodata & \nodata & & CXOGCJ174529.6-290021 & 266.37375 & -29.00607 & hard & 0.57 \\ SSTGC 0496815 & 266.37359 & -29.04089 & 9.32 & 9.20 & \nodata & \nodata & & CXOGCJ174529.6-290227 & 266.37363 & -29.04084 & hard & 0.23 \\ SSTGC 0498139 & 266.37558 & -29.04694 & 9.15 & 8.53 & 8.12 & 8.32 & & CXOGCJ174530.0-290248 & 266.37530 & -29.04681 & hard & 1.00 \\ SSTGC 0498461 & 266.37611 & -29.06168 & 10.29 & 10.24 & 10.02 & \nodata & & CXOGCJ174530.3-290341 & 266.37628 & -29.06157 & hard & 0.67 \\ SSTGC 0500061 & 266.37851 & -29.02794 & 7.03 & 5.84 & 5.04 & 4.79 & & CXOGCJ174530.8-290139 & 266.37864 & -29.02777 & hard & 0.73 \\ SSTGC 0502935 & 266.38299 & -29.04974 & 7.01 & 6.92 & 6.51 & 6.44 & & CXOGCJ174531.9-290258 & 266.38306 & -29.04952 & hard & 0.83 \\ SSTGC 0503729 & 266.38422 & -29.02490 & \nodata & 9.80 & \nodata & \nodata & & CXOGCJ174532.1-290130 & 266.38416 & -29.02509 & hard & 0.72 \\ SSTGC 0503925 & 266.38452 & -29.05826 & \nodata & 10.48 & \nodata & \nodata & & CXOGCJ174532.2-290329 & 266.38439 & -29.05829 & hard & 0.43 \\ SSTGC 0504458 & 266.38536 & -28.98557 & 9.86 & 9.96 & 9.64 & \nodata & & CXOGCJ174532.5-285908 & 266.38566 & -28.98556 & hard & 0.94 \\ SSTGC 0505766 & 266.38734 & -29.07664 & 10.91 & 10.56 & \nodata & \nodata & & CXOGCJ174532.8-290436 & 266.38703 & -29.07670 & hard & 1.00 \\ SSTGC 0507145 & 266.38945 & -28.94431 & 10.81 & 10.43 & 9.89 & \nodata & & CXOGCJ174533.4-285638 & 266.38941 & -28.94415 & soft & 0.58 \\ SSTGC 0508028 & 266.39072 & -28.95800 & 11.45 & 10.97 & \nodata & \nodata & & CXOGCJ174533.7-285728 & 266.39077 & -28.95803 & soft & 0.19 \\ SSTGC 0507814 & 266.39043 & -29.07579 & 9.62 & 8.73 & 8.37 & \nodata & & CXOGCJ174533.7-290432 & 266.39053 & -29.07578 & hard & 0.32 \\ SSTGC 0508562 & 266.39155 & -28.99906 & 9.42 & \nodata & \nodata & \nodata & & CXOGCJ174534.0-285956 & 266.39182 & -28.99901 & hard & 0.87 \\ SSTGC 0510334 & 266.39416 & -29.04338 & 7.98 & 7.73 & 7.17 & 6.47 & & CXOGCJ174534.5-290236 & 266.39409 & -29.04357 & hard & 0.73 \\ SSTGC 0510970 & 266.39515 & -29.07890 & 7.48 & 7.39 & 6.80 & 6.98 & & CXOGCJ174534.8-290444 & 266.39535 & -29.07906 & hard & 0.84 \\ SSTGC 0511940 & 266.39659 & -28.97869 & \nodata & \nodata & 8.27 & \nodata & & CXOGCJ174535.1-285843 & 266.39633 & -28.97877 & hard & 0.87 \\ SSTGC 0511999 & 266.39668 & -29.01359 & 8.57 & 8.45 & 7.86 & 7.22 & & CXOGCJ174535.2-290048 & 266.39689 & -29.01352 & hard & 0.71 \\ SSTGC 0512567 & 266.39755 & -28.93489 & 9.50 & 9.57 & 9.27 & \nodata & & CXOGCJ174535.4-285605 & 266.39763 & -28.93492 & hard & 0.28 \\ SSTGC 0514496 & 266.40052 & -28.94409 & 8.82 & 8.26 & 7.97 & 7.82 & & CXOGCJ174536.1-285638 & 266.40059 & -28.94407 & soft & 0.23 \\ SSTGC 0514528 & 266.40057 & -28.96362 & 10.20 & 10.36 & 9.89 & \nodata & & CXOGCJ174536.1-285748 & 266.40067 & -28.96347 & hard & 0.62 \\ SSTGC 0514886 & 266.40111 & -28.97721 & \nodata & \nodata & \nodata & 8.17 & & CXOGCJ174536.3-285837 & 266.40125 & -28.97712 & hard & 0.55 \\ SSTGC 0515077 & 266.40139 & -29.02929 & 10.73 & 10.41 & \nodata & \nodata & & CXOGCJ174536.3-290145 & 266.40150 & -29.02919 & soft & 0.51 \\ SSTGC 0515409 & 266.40189 & -29.02083 & 9.30 & \nodata & \nodata & \nodata & & CXOGCJ174536.4-290114 & 266.40181 & -29.02067 & hard & 0.64 \\ SSTGC 0517465 & 266.40502 & -28.98550 & 8.15 & 8.16 & 7.79 & \nodata & & CXOGCJ174537.2-285906 & 266.40502 & -28.98526 & hard & 0.87 \\ SSTGC 0518345 & 266.40641 & -29.03129 & 10.04 & 9.92 & 9.80 & \nodata & & CXOGCJ174537.5-290153 & 266.40653 & -29.03142 & hard & 0.62 \\ SSTGC 0518659 & 266.40684 & -29.00667 & 9.45 & \nodata & \nodata & \nodata & & CXOGCJ174537.6-290023 & 266.40683 & -29.00657 & hard & 0.36 \\ SSTGC 0519255 & 266.40776 & -29.02434 & 9.93 & 9.76 & 8.65 & 7.41 & & CXOGCJ174537.8-290127 & 266.40757 & -29.02426 & soft & 0.66 \\ SSTGC 0519545 & 266.40824 & -29.02626 & 8.25 & 8.13 & \nodata & \nodata & & CXOGCJ174537.9-290134 & 266.40831 & -29.02622 & soft & 0.26 \\ SSTGC 0520087 & 266.40907 & -28.98803 & \nodata & \nodata & 8.26 & \nodata & & CXOGCJ174538.1-285916 & 266.40878 & -28.98805 & hard & 0.92 \\ SSTGC 0520903 & 266.41025 & -28.96968 & 8.50 & 8.45 & 7.91 & 7.69 & & CXOGCJ174538.4-285810 & 266.41031 & -28.96958 & hard & 0.40 \\ SSTGC 0521476 & 266.41115 & -29.01893 & \nodata & 8.51 & \nodata & \nodata & & CXOGCJ174538.6-290107 & 266.41101 & -29.01889 & hard & 0.47 \\ SSTGC 0522739 & 266.41312 & -28.96061 & 9.19 & 9.22 & 8.79 & 8.46 & & CXOGCJ174539.1-285738 & 266.41308 & -28.96081 & hard & 0.73 \\ SSTGC 0522856 & 266.41327 & -29.04730 & 11.06 & 8.88 & 8.23 & 8.20 & & CXOGCJ174539.2-290250 & 266.41356 & -29.04738 & hard & 0.95 \\ SSTGC 0523283 & 266.41392 & -29.00467 & 8.12 & \nodata & \nodata & \nodata & & CXOGCJ174539.3-290016 & 266.41397 & -29.00467 & soft & 0.16 \\ SSTGC 0523729 & 266.41463 & -29.02514 & 9.49 & 8.94 & 8.81 & \nodata & & CXOGCJ174539.5-290129 & 266.41465 & -29.02499 & hard & 0.54 \\ SSTGC 0524504 & 266.41584 & -29.00847 & 5.63 & \nodata & \nodata & \nodata & & CXOGCJ174539.7-290029 & 266.41567 & -29.00827 & soft & 0.91 \\ SSTGC 0525460 & 266.41726 & -28.99969 & 6.18 & 4.59 & 3.16 & 1.69 & & CXOGCJ174540.1-285957 & 266.41718 & -28.99944 & hard & 0.92 \\ SSTGC 0525510 & 266.41735 & -29.01540 & 8.21 & \nodata & 6.98 & \nodata & & CXOGCJ174540.1-290055 & 266.41733 & -29.01546 & soft & 0.23 \\ SSTGC 0525714 & 266.41765 & -28.98358 & 8.52 & 8.46 & 7.72 & 6.99 & & CXOGCJ174540.2-285900 & 266.41753 & -28.98360 & hard & 0.38 \\ SSTGC 0526867 & 266.41944 & -28.94462 & \nodata & \nodata & \nodata & 8.58 & & CXOGCJ174540.6-285640 & 266.41950 & -28.94445 & soft & 0.65 \\ SSTGC 0527316 & 266.42016 & -29.03007 & \nodata & \nodata & 8.12 & \nodata & & CXOGCJ174540.8-290149 & 266.42011 & -29.03029 & hard & 0.80 \\ SSTGC 0527347 & 266.42020 & -29.05794 & 11.12 & \nodata & \nodata & \nodata & & CXOGCJ174540.8-290328 & 266.42037 & -29.05804 & soft & 0.65 \\ SSTGC 0527844 & 266.42100 & -29.00472 & 8.56 & 7.16 & \nodata & \nodata & & CXOGCJ174541.0-290017 & 266.42095 & -29.00489 & hard & 0.62 \\ SSTGC 0529789 & 266.42400 & -29.00790 & 9.01 & \nodata & \nodata & \nodata & & CXOGCJ174541.7-290027 & 266.42377 & -29.00774 & hard & 0.93 \\ SSTGC 0530322 & 266.42482 & -28.99881 & \nodata & \nodata & 8.47 & \nodata & & CXOGCJ174541.9-285955 & 266.42473 & -28.99865 & hard & 0.65 \\ SSTGC 0531615 & 266.42680 & -28.96723 & \nodata & \nodata & \nodata & 9.28 & & CXOGCJ174542.4-285802 & 266.42678 & -28.96724 & hard & 0.07 \\ SSTGC 0532179 & 266.42763 & -28.95284 & 11.30 & 10.80 & \nodata & \nodata & & CXOGCJ174542.6-285709 & 266.42768 & -28.95257 & hard & 0.99 \\ SSTGC 0532570 & 266.42818 & -28.97533 & 9.54 & 9.29 & 8.87 & \nodata & & CXOGCJ174542.7-285831 & 266.42816 & -28.97552 & hard & 0.68 \\ SSTGC 0533119 & 266.42903 & -29.07535 & \nodata & 10.74 & \nodata & \nodata & & CXOGCJ174542.9-290431 & 266.42890 & -29.07535 & soft & 0.41 \\ SSTGC 0533640 & 266.42983 & -29.01391 & 7.39 & 6.73 & 6.11 & 5.85 & & CXOGCJ174543.1-290049 & 266.42961 & -29.01382 & soft & 0.76 \\ SSTGC 0533886 & 266.43016 & -28.98839 & 10.20 & 10.18 & 9.59 & \nodata & & CXOGCJ174543.2-285917 & 266.43035 & -28.98822 & hard & 0.85 \\ SSTGC 0534588 & 266.43123 & -28.98360 & 9.10 & \nodata & 9.08 & \nodata & & CXOGCJ174543.4-285900 & 266.43102 & -28.98341 & hard & 0.96 \\ SSTGC 0534566 & 266.43120 & -29.06347 & 8.47 & 8.36 & 7.85 & 7.97 & & CXOGCJ174543.4-290347 & 266.43106 & -29.06327 & hard & 0.83 \\ SSTGC 0535312 & 266.43230 & -29.02660 & 11.89 & 10.66 & \nodata & \nodata & & CXOGCJ174543.7-290136 & 266.43234 & -29.02668 & hard & 0.32 \\ SSTGC 0535628 & 266.43280 & -29.04581 & 9.84 & 9.81 & 9.31 & \nodata & & CXOGCJ174543.9-290245 & 266.43309 & -29.04590 & hard & 0.96 \\ SSTGC 0535765 & 266.43300 & -29.08237 & 9.46 & 9.48 & 9.43 & 9.48 & & CXOGCJ174543.9-290456 & 266.43305 & -29.08238 & soft & 0.16 \\ SSTGC 0536043 & 266.43341 & -29.07468 & 10.24 & 9.67 & 9.44 & 9.04 & & CXOGCJ174544.0-290428 & 266.43363 & -29.07460 & hard & 0.75 \\ SSTGC 0537314 & 266.43533 & -28.97495 & 9.36 & 8.80 & 8.24 & 7.83 & & CXOGCJ174544.4-285829 & 266.43531 & -28.97486 & hard & 0.32 \\ SSTGC 0537395 & 266.43544 & -28.97053 & \nodata & \nodata & 6.76 & \nodata & & CXOGCJ174544.5-285813 & 266.43557 & -28.97044 & hard & 0.52 \\ SSTGC 0537801 & 266.43609 & -29.06095 & 12.55 & \nodata & \nodata & \nodata & & CXOGCJ174544.7-290339 & 266.43631 & -29.06109 & hard & 0.87 \\ SSTGC 0539467 & 266.43859 & -28.97468 & 10.76 & 10.45 & \nodata & \nodata & & CXOGCJ174545.2-285828 & 266.43870 & -28.97466 & soft & 0.36 \\ SSTGC 0539388 & 266.43847 & -29.04029 & 12.23 & 12.24 & \nodata & \nodata & & CXOGCJ174545.2-290224 & 266.43840 & -29.04009 & soft & 0.75 \\ SSTGC 0543526 & 266.44459 & -29.05783 & 10.56 & \nodata & \nodata & \nodata & & CXOGCJ174546.6-290328 & 266.44449 & -29.05786 & soft & 0.33 \\ SSTGC 0543690 & 266.44482 & -29.03528 & \nodata & \nodata & \nodata & 8.35 & & CXOGCJ174546.7-290207 & 266.44473 & -29.03552 & hard & 0.92 \\ SSTGC 0544019 & 266.44530 & -29.04789 & 9.47 & 8.58 & 7.83 & \nodata & & CXOGCJ174546.8-290252 & 266.44521 & -29.04789 & soft & 0.28 \\ SSTGC 0546444 & 266.44903 & -28.94019 & 7.82 & 7.48 & 6.85 & 6.78 & & CXOGCJ174547.7-285624 & 266.44899 & -28.94008 & hard & 0.41 \\ SSTGC 0547195 & 266.45015 & -29.05055 & 7.54 & 7.26 & 6.80 & 6.89 & & CXOGCJ174548.0-290301 & 266.45010 & -29.05040 & hard & 0.55 \\ SSTGC 0548119 & 266.45158 & -28.99872 & \nodata & \nodata & 9.94 & \nodata & & CXOGCJ174548.4-285954 & 266.45179 & -28.99852 & hard & 0.97 \\ SSTGC 0548472 & 266.45212 & -28.96311 & 10.88 & 10.62 & \nodata & \nodata & & CXOGCJ174548.5-285747 & 266.45240 & -28.96309 & hard & 0.88 \\ SSTGC 0548665 & 266.45244 & -29.04621 & 11.93 & \nodata & \nodata & \nodata & & CXOGCJ174548.5-290246 & 266.45248 & -29.04616 & soft & 0.23 \\ SSTGC 0550312 & 266.45497 & -29.02723 & 10.71 & 10.72 & 10.67 & \nodata & & CXOGCJ174549.1-290137 & 266.45492 & -29.02721 & soft & 0.18 \\ SSTGC 0550210 & 266.45481 & -29.08411 & 10.33 & 9.94 & 9.58 & 9.10 & & CXOGCJ174549.1-290502 & 266.45467 & -29.08396 & soft & 0.71 \\ SSTGC 0550863 & 266.45578 & -28.95373 & 8.27 & 8.02 & 7.54 & 7.52 & & CXOGCJ174549.4-285712 & 266.45597 & -28.95356 & hard & 0.87 \\ SSTGC 0553475 & 266.45968 & -29.00568 & 12.25 & 11.87 & \nodata & \nodata & & CXOGCJ174550.2-290020 & 266.45948 & -29.00566 & hard & 0.63 \\ SSTGC 0554271 & 266.46090 & -28.98878 & 9.63 & 9.00 & 8.63 & 7.90 & & CXOGCJ174550.6-285919 & 266.46096 & -28.98886 & soft & 0.36 \\ SSTGC 0554555 & 266.46134 & -29.07635 & 12.52 & 11.67 & \nodata & \nodata & & CXOGCJ174550.7-290434 & 266.46159 & -29.07628 & soft & 0.83 \\ SSTGC 0558398 & 266.46721 & -28.96776 & 9.82 & 9.85 & 9.51 & \nodata & & CXOGCJ174552.1-285804 & 266.46722 & -28.96790 & soft & 0.50 \\ SSTGC 0559457 & 266.46887 & -28.99130 & \nodata & \nodata & 7.42 & \nodata & & CXOGCJ174552.5-285928 & 266.46878 & -28.99131 & hard & 0.29 \\ SSTGC 0560119 & 266.46985 & -29.03013 & 10.41 & \nodata & \nodata & \nodata & & CXOGCJ174552.7-290148 & 266.46965 & -29.03021 & hard & 0.69 \\ SSTGC 0564995 & 266.47723 & -29.04817 & 11.86 & 11.62 & \nodata & \nodata & & CXOGCJ174554.5-290252 & 266.47709 & -29.04805 & soft & 0.62 \\ SSTGC 0570573 & 266.48573 & -28.96011 & 10.59 & 10.53 & 11.08 & \nodata & & CXOGCJ174556.5-285736 & 266.48560 & -28.96019 & soft & 0.50 \\ SSTGC 0572280 & 266.48837 & -29.05031 & 9.12 & 9.07 & 8.67 & \nodata & & CXOGCJ174557.2-290301 & 266.48852 & -29.05042 & hard & 0.61 \\ SSTGC 0572559 & 266.48879 & -28.96801 & 9.52 & 9.09 & \nodata & \nodata & & CXOGCJ174557.3-285804 & 266.48899 & -28.96787 & hard & 0.80 \\ SSTGC 0575612 & 266.49335 & -29.02236 & 8.91 & 8.90 & 8.62 & 8.92 & & CXOGCJ174558.4-290120 & 266.49364 & -29.02232 & soft & 0.93 \\ SSTGC 0577500 & 266.49625 & -29.04868 & 10.02 & 9.83 & 9.44 & 10.04 & & CXOGCJ174559.1-290255 & 266.49640 & -29.04875 & hard & 0.53 \\ SSTGC 0578722 & 266.49813 & -29.00052 & 10.09 & 9.93 & 9.74 & \nodata & & CXOGCJ174559.5-290002 & 266.49806 & -29.00067 & soft & 0.59 \\ SSTGC 0579221 & 266.49888 & -28.98583 & 9.61 & 9.60 & 9.26 & 9.22 & & CXOGCJ174559.7-285908 & 266.49881 & -28.98571 & hard & 0.47 \\ SSTGC 0580810 & 266.50121 & -29.01808 & \nodata & 11.52 & \nodata & \nodata & & CXOGCJ174600.2-290105 & 266.50108 & -29.01809 & soft & 0.41 \\ SSTGC 0588034 & 266.51210 & -29.01352 & \nodata & 10.80 & \nodata & \nodata & & CXOGCJ174602.8-290049 & 266.51202 & -29.01366 & hard & 0.56 \\ \enddata \tablecomments{Positional coincidence does not necessarily imply a physical association of IR and X--ray sources. In fact, $\sim70\%$ of the objects on this list are likely to be random positional coincidences of unrelated sources along the line of sight.} \tablenotetext{a}{soft = detected in the 0.5--2.0 keV band; hard = not detected in the 0.5--2.0 keV band.} \tablenotetext{b}{Separation between IR and X-ray source positions.} \end{deluxetable} \clearpage \end{document}