2 Observations and data analysis

The observations used in this analysis were carried out with the PSPC detector on-board the ROSAT observatory during nine pointed observations between 8 October 1991 and 14 October 1993. The satellite, its X-ray telescope (XRT) and the focal plane detector (PSPC) used were discussed in detail by Trümper (1983) and Pfeffermann et al. (1986). The pointings were performed in a raster covering the Optical Bar and the Eastern Wing of the SMC quite homogeneously (cf. Fig. 1, Fig. 2 and Table 1 in Kahabka & Pietsch 1996, herafter Paper I). A search for unresolved and moderately extended sources has been conducted on the data obtained from these fields (Table 2).

  

Table 2: Fields used for source search in the SMC Survey

A sophisticated detection procedure was applied to the SMC survey. Each pointed observation has been analyzed with three detection methods (local, map and maximum likelihood, cf. Zimmermann et al. 1994). These detection procedures were applied to the data of single pointings given in Table 2. Data with the same pointing direction have been merged to one data set. The analysis was performed in the five energy channel ranges Soft = (channel 11-41, 0.1-0.4 keV), Hard = (channel 52-201, 0.5-2.1 keV), Hard1 = (channel 52-90, 0.5-0.9 keV), Hard2 = (channel 91-201, 0.9-2.0 keV) and Broad (0.1-2.4 keV). The five source lists were merged to one final source list taking only detections at an off-axis angle $\le45'$ into account. This list comprises the source catalogue published in this paper. The maximum likelihood algorithm was used to determine the final source position, the counts in five energy bands and the source extent. A one-dimensional energy and position dependent Gaussian distribution (cf. Zimmermann et al. 1994) was applied in order to obtain the source extent. The source extent (Ext) is given as the Gaussian $\sigma_{\rm Gauss}$

$$Ext = \sigma_{\rm Gauss} = FWHM_{\rm Gauss} / 2.35.$$ (1)

Hardness ratios HR1 and HR2 were calculated from the counts in the bands as HR1=(H-S)/(H+S) and HR2=(H2-H1)/(H1+H2). The existence likelihood ratio and the extent likelihood ratio was calculated according to Cash (1979) and Cruddace et al. (1988).