2 ROSAT PSPC observations and analysis

ROSAT performed 31 pointed PSPC observations with at least 200 s of exposure in a 6$^\circ$$\times$6$^\circ$ area centered on the position RA = 01$^{\rm h}$ 00$^{\rm m}$ 00$^{\rm s}$ Dec = -73$^\circ$ 30$^\prime$ 00 $^{\prime\prime}$ in the SMC between 1990 and 1994. Most of the observations (summarized in Table 1) had exposures between 5 ks and 20 ks and in one case reached 64.6 ks (centered on CF Tuc).

An X-ray image of the SMC produced from merged ROSAT PSPC data in the energy band 0.5 - 2.0 keV is shown in Fig. 1. The image is exposure corrected but not background subtracted and covers an exposed area of $\sim$18 square degrees. Time intervals with a total count rate of more than 15 cts s^-1 were excluded to keep the background at the lowest possible level and uniform in the image. The image was binned to 1536$\times$1536 pixels of 15 $^{\prime\prime}$$\times$15 $^{\prime\prime}$ size and smoothed with an intensity dependent Gaussian filter before the exposure correction (stronger smoothing at the low intensity levels and no smoothing above 15 counts per pixel to avoid smearing out the stronger point sources). The still visible blurring is caused by the telescope when sources are observed far off-axis (see the sources at the rim of the exposures). For this reason conclusions on possible diffuse emission in the SMC require a more careful quantitative study beyond the scope of this paper. A wealth of X-ray sources is detected in the ROSAT PSPC data with most sources concentrated in the northern part of the SMC. The combination of three images in the energy bands 0.1 - 0.4 keV, 0.5 - 0.9 keV and 0.9 - 2.0 keV into a red-green-blue (RGB) image is shown in Fig. 2. The colours illustrate the different X-ray spectra of various source types. Sources with soft X-ray spectra (high intensities in the "red" 0.1 - 0.4 keV band) like foreground stars and in particular SSSs appear in orange/red. SNRs are characterized by harder spectra and green to blue colours. Absorbed AGN and X-ray binaries show the hardest X-ray spectra and blue colours in the RGB image.

 

 

Table 1: ROSAT PSPC observations of the SMC region

ID	Exp.	Date	RA	Dec
	s	begin  end		(J2000.0)
201094p	64636	921002 921111	00 50 48.00	-74 46 48.0
300369p	5640	930928 931101	01 22 55.02	-75 21 00.0
300369p-1	213	940401 940401	01 22 55.02	-75 21 00.0
400022p	16634	911007 911008	01 17 04.08	-73 26 24.0
400022p-1	8985	920930 921002	01 17 04.08	-73 26 24.0
400022p-2	11864	930603 930604	01 17 04.08	-73 26 24.0
400149p	6281	920428 920603	00 37 19.02	-72 14 24.0
400299p	5121	930410 930424	00 37 19.02	-72 14 24.0
400299p-1	1677	931002 931009	00 37 19.02	-72 14 24.0
400299p-2	2311	940503 940505	00 37 19.02	-72 14 24.0
400300p	5214	930329 930330	00 58 33.06	-71 36 00.0
400300p-1	7199	931001 931009	00 58 33.06	-71 36 00.0
400300p-2	4111	940505 940505	00 58 33.06	-71 36 00.0
500142p	4909	930512 930513	01 04 02.04	-72 01 48.0
500249p	19262	931105 931109	00 46 40.08	-73 12 36.0
500250p	20860	931014 931029	01 04 38.04	-72 05 23.5
500251p	2093	931130 931130	00 51 19.02	-73 24 00.0
600195p-0	16644	911008 911103	00 58 12.00	-72 16 48.0
600195p-1	9443	920417 920427	00 58 12.00	-72 16 48.0
600196p-0	1303	911009 911102	00 50 45.06	-73 13 48.0
600196p-1	22223	920415 920425	00 50 45.06	-73 13 48.0
600197p	21494	911016 911019	01 13 24.00	-72 49 12.0
600452p	14207	930410 930425	01 05 55.02	-72 33 35.5
600452p-1	16663	931001 931014	01 05 55.02	-72 33 35.5
600453p	17593	930509 930512	00 54 28.08	-72 45 36.0
600454p	9727	921205 921208	00 42 55.02	-73 38 24.0
600454p-1	8299	930405 930426	00 42 55.02	-73 38 24.0
600455p	3561	921206 921206	01 01 16.08	-71 49 12.0
600455p-1	1721	930416 930422	01 01 16.08	-71 49 12.0
600455p-2	4595	931007 931010	01 01 16.08	-71 49 12.0
600455p-3	4129	940504 940505	01 01 16.08	-71 49 12.0

We used the EXSAS software package (Zimmermann et al. 1994) for the analysis of the individual pointings and followed the same lines as in HP99 for the LMC. However, the 31 SMC observations covered 16 different fields and pointings in the same direction were merged to gain sensitivity. In these cases both merged and individual images were run through the source detection procedure. After the final visual inspection of the source list a catalogue of 517 point-like and weakly extended sources was obtained with source properties as given in the LMC catalogue of HP99. Both catalogues comprise complementary lists of sources detected with the ROSAT PSPC in the fields of the MCs.

Figure 1: Exposure corrected 0.5 - 2.0 keV image of the combined ROSAT PSPC observations in the SMC region

Figure 2: PSPC images in the energy bands 0.1 - 0.4 keV, 0.5 - 0.9 keV and 0.9 - 2.0 keV combined into a red-green-blue (RGB) colour coded image