4 Conclusion

 

 

Table 2: Number of classified X-ray sources in the LMC and SMC observed by the HRI

1	2	3	4	5
Source	LMC		SMC
class	id.+cand.	new	id.+cand.	new
SNR	24 + 4	5	6 + 1
SSS	5		4
XB	9 + 1	2	12 + 15
AGN	9 + 1		1 + 9	1
hard (XB or AGN)		3		6
foreground star	39 + 2		4 + 2	8

Notes to Cols. Nos. 2 and 4:

X-ray sources identified with known sources in catalogues and literature + candidates reported in literature.

Notes to Cols. Nos. 3 and 5:

New classifications of SHP00 and this work.

Analyzing the whole set of 71 ROSAT HRI pointings of the SMC region we obtained a catalogue containing 121 discrete X-ray sources. Sources were searched both in single pointings and merged data applying a maximum likelihood algorithm. The high spatial resolution of the HRI allowed us to identify X-ray sources with optically observed objects in the TYCHO catalogue or the SIMBAD data base and to reduce the systematic boresight errors. In total coordinates of 99 HRI sources were corrected and the positional errors reduced to 5 $.\!\!^{\prime\prime}$6 on average.

By searching through literature 56 HRI sources were identified with already classified objects belonging to SMC SSSs, XBs, SNRs, background AGN, or foreground stars. Figure 9 shows HRI sources which are identified with objects of different source classes known from various catalogues and literature, plotted over an 0.1 - 2.4 keV PSPC image. The HRI observations mostly covered the main body of the SMC (see Fig. 1), which is the reason that most of the identified and new sources are located in this region (see Fig. 10). In this work 15 sources are newly classified as foreground star, XB, or AGN. There are still 50 unclassified HRI detections well distributed over the field observed by the HRI. The source distribution shows that there is a deficiency of X-ray sources in the central part of the SMC around RA = 00$^{\rm h}$ 55$^{\rm m}$, Dec = -72 $\hbox{$^\circ$ }\$ 40 $\hbox{$^\prime$ }\$(J2000.0).

In Table 2 the numbers of detected sources are compared between the LMC and the SMC. In the LMC the number of SNRs is larger than in the SMC by a factor of four roughly in accordance with the ratio of the areas covered by the observations. The number of known SSSs and X-ray binaries detected in ROSAT observations is comparable in the two clouds, most of the XBs are binary systems with Be-star companions. Nevertheless the number of XB candidates in the SMC is relatively higher than in the LMC maybe partly due to the fact that a thorough search for Be/X-ray binary candidates has been done for the SMC by comparing the X-ray catalogues with the catalogues of emission line objects (HS00).

Based on all available ROSAT HRI pointing data complete HRI source catalogues both for the LMC and for the SMC are now available. They summarize the detections of X-ray sources in the MCs and provide accurate positions with errors smaller than 16 $^{\prime\prime}$ for all sources, for the majority of sources about 8 $^{\prime\prime}$. Verification of the candidates for the different source classes by a final optical identification is still needed. Additional observations in the future will achieve more precise characterization of the sources giving a better overall picture of the MCs.

Acknowledgements

The ROSAT project is supported by the German Bundesministerium für Bildung und Forschung (BMBF) and the Max-Planck-Gesellschaft. This research has been carried out by making extensive use of the SIMBAD data base operated at CDS, Strasbourg, France, and data obtained through the High Energy Astrophysics Science Archive Research Center Online Service, provided by the NASA/Goddard Space Flight Center.

  

Table 3: Identified HRI sources in the SMC

Notes to Col. No. 9 (Table 3), No. 10 (Tables 4 and 5): Catalogue number from [HFPK00].
Notes to Col. No. 12 (Table 3), No. 13 (Tables 4 and 5): Candidates from literature are marked with? behind the source class. New classification of this work are put in < >.
Abbreviation for references in square brackets are given in the literature list.

 

Table 3: continued

  

Table 4: Classified HRI sources

  

Table 5: HRI sources in the SMC region

Notes to Col. No. 6: HRI count rate ist the output value from maximum likelihood algorithm with the smallest positional error.
Notes to Col. No. 9: For sources which are listed in [HFPK00] PSPC count rates are taken from the PSPC catalogue. Otherwise PSPC count rate is the 95.4 % $2 \sigma$ upper limit mawimum likelihood algorithm of the pointing with maximum exposure.

 

Table 5: continued

 

Table 5: continued