3. Source identification

The comparison of the Parkes radio and the ROSAT X-ray surveys of the LMC resulted in the discovery of 71 sources common to both surveys. A similar comparison was undertaken for the SMC field and resulted in the discovery of 27 sources common to both surveys. Each source lies within 2.5 of its counterpart; this is the basic criterion for positive source identification. This criterion was chosen according to the upper limit of positional uncertainties at our 1.4 GHz survey which is 2 at the 1 level (Paper IV). The most accurate radio positions available are from the highest radio-frequency survey in which the sources appear. These positions were compared with X-ray positions from Pietsch et al. (in preparation) and Kahabka et al. (in preparation).

In Table 2 (click here), we present data for the 71 sources in common towards the LMC and in Table 3 (click here), we list the 27 sources in common towards the SMC. Columns 2 and 3 of Tables 2 (click here) and  3 (click here) give the radio-source and X-ray source names respectively. Column 4 lists the source radio flux density at 4.75 GHz (4.85 GHz for the SMC). For eight LMC and five SMC sources the flux density at 4.75 GHz (4.85 GHz for the SMC) was estimated by interpolation from other radio frequencies; these sources are flagged in Col. 4. The X-ray information, count rate and HR2, are listed for each source in Col. 5 and Col. 7 respectively.

Column 6 lists the source radio spectral index () and error () as defined by the relationship , where is flux density and is frequency. In order to extend the radio frequency coverage and to obtain more accurate radio spectral indices we have also used some flux densities from other radio catalogues; Clarke et al. (1976) at 0.408 GHz, Mills et al. (1984) at 0.843 GHz and Milne et al. (1980) at 14.7 GHz. Spectral indices are not given for 10 LMC and six SMC sources which were detected at only one radio frequency or for which radio data are only available at two close frequencies (4.75 GHz and 4.85 GHz).

Column 8 of Tables 2 (click here) and  3 (click here) gives the "radio source type'' based on published references (Col. 9); these sources are marked with capital letters BG (background sources), HII regions and SNR. In the case of SNRs, where applicable, we have divided the sources into one of five different types: SNR1 to SNR5 respectively (type 1 - evolved SNRs, type 2 - Oxygen-rich SNRs, type 3 - Balmer-dominated SNRs, type 4 - Crab-like SNRs and type 5 - possible type III SNRs). This follows the classification of Mathewson et al. (1983a). Note that capitals (BG, SNR and HII) were used for classifications from previous works and lower case (bg and snr) for sources classified here. The question-mark indicates probable but not certain classification. The criteria by which we classify these sources are discussed in Sect. 4.1.

A cross-check of all 71 sources towards the LMC and 27 sources towards the SMC has been made with a wide range of catalogues that contain discrete sources towards the MCs (Col. 10). The catalogues used are given as a footnote to Tables  2 (click here) and  3 (click here). Some comments regarding the discrete sources are given in Col. 11.

   

(1) (2) (3) (4) (5) (6) (7) (8) (9)

No. Radio X-Ray S_4.75 Count Rate HR 2 Type

Source Name Source Name (Jy) cts ks^-1

1 LMCB0428-6755 LMCRASS9001 0.240 4.8 1.00 BG 7; 25

2 LMCB0438-7316 LMCRASS66 0.1080 27.4 0.07 bg

3 LMCB0441-6957 LMCRASS75 0.2580 5.2 0.51 bg

4 LMCB0442-6824 LMCRASS78 0.047 7.7 0.28 bg

5 LMCB0445-6458 LMCRASS84 0.085 59.6 0.07 bg

6 LMCB0446-7210 LMCRASS9002 0.091 12.1 0.68 bg

7 LMCB0453-6834 LMCRASS100 0.140 410.1 -0.30 SNR 20; 22; 27

8 LMCB0454-6630 LMCRASS103 0.060 23.7 -1.00 SNR 5; 13; 20; 22; 27; 28

9 LMCB0454-6718 LMCRASS102 37.4 -0.33 SNR 4

10 LMCB0454-6806 LMCRASS9003 0.058 7.2 0.38 ?

11 LMCB0455-6843 LMCRASS104 0.141 16.4 -0.07 SNR 5; 8; 20; 22; 27; 28

12 LMCB0456-6803 LMCRASS106 6.4 0.03 ?

13 LMCB0502-6638 LMCRASS125 0.033 70.9 0.20 BG

14 LMCB0506-6806 LMCRASS136 0.226 926.7 -0.20 SNR

15 LMCB0507-6829 LMCRASS141 0.245 5.0 -0.61 SNR? 8

16 LMCB0507-7029 LMCRASS139 0.146 27.1 0.52 SNR? 8

17 LMCB0508-6436 LMCRASS146 0.077 17.3 0.14 bg

18 LMCB0509-6848 LMCRASS149 0.529 1322.7 0.22 SNR4 13; 14; 20; 22; 27; 28

19 LMCB0513-6729 LMCRASS9004 0.186 3.2 1.00 ?

20 LMCB0513-6915 LMCRASS166 0.264 8.7 -0.27 SNR1 23

21 LMCB0519-6905 LMCRASS183 0.072^f 1273.1 0.03 SNR3 13; 14; 20; 22; 27; 35

22 LMCB0519-6941 LMCRASS180 0.866 16.2 -0.32 SNR 1; 13; 19; 20; 22; 27; 28; 30

23 LMCB0520-6928 LMCRASS185 0.111 81.9 0.14 SNR 22; 27

24 LMCB0522-6757 LMCRASS192 0.236 89.3 -0.05 SNR 6; 13; 20; 26; 28; 54

25 LMCB0523-6623 LMCRASS9005 0.100 4.5 1.00 ?

26 LMCB0524-6443 LMCRASS202 0.043 7.7 0.49 bg

27 LMCB0525-6601 LMCRASS205 0.390 1010.3 -0.04 SNR5 15; 20; 22; 27; 28; 29

28 LMCB0525-6607 LMCRASS207 1.009 1487.8 0.02 SNR5 1; 5; 9; 13; 15; 22; 27; 28; 36; 50

29 LMCB0525-6941 LMCRASS203 2.251 8764.9 0.02 SNR2 1; 13; 14; 17; 20; 22; 27; 28

30 LMCB0528-6542 LMCRASS9006 0.035 2.2 0.32 ?

31 LMCB0528-6551 LMCRASS213 0.108 12.3 -0.24 SNR 8; 22; 27

32 LMCB0528-6838 LMCRASS214 0.210 18.8 -0.13 snr?

33 LMCB0528-6914 LMCRASS210 0.075 14.2 -0.05 SNR1 27; 42

34 LMCB0530-6655 LMCRASS220 0.100 15.0 -0.55 snr?

35 LMCB0531-6518 LMCRASS223 0.041 31.3 0.44 bg?

36 LMCB0532-6734 LMCRASS229 0.093 69.0 -0.35 SNR? 23; 37

37 LMCB0532-7102 LMCRASS225 0.382^f 49.6 -0.50 SNR 20; 22; 27

38 LMCB0534-6438 LMCRASS9007 0.058 6.9 0.89 bg

39 LMCB0534-6957 LMCRASS237 0.054 194.7 -0.28 SNR1 20; 22; 27

40 LMCB0534-7035 LMCRASS239 0.067 31.3 0.06 SNR 20; 22; 24; 27

41 LMCB0534-7204 LMCRASS236 0.103 5.4 -0.89 snr?

42 LMCB0535-6603 LMCRASS245 0.701 5508.2 0.02 SNR4 1; 9; 10; 13; 15; 22; 27; 28; 33; 39

43 LMCB0536-6452 LMCRASS250 0.050 25.2 0.13 bg

44 LMCB0536-6735 LMCRASS247 0.133^f 49.8 0.37 SNR1 23

45 LMCB0536-7040 LMCRASS248 0.025 39.4 0.40 SNR 20; 22; 24; 27

46 LMCB0537-6506 LMCRASS253 0.035 30.8 0.50 bg?

47 LMCB0538-6911 LMCRASS254 3.571 142.9 0.55 SNR4 5; 9; 11; 13; 20; 22; 27; 28

48 LMCB0539-6907 LMCRASS9008 35.787 27.4 0.32 HII 1; 2; 3; 25; 31; 33; 46; 47; 54

49 LMCB0540-6921 LMCRASS265 0.980 0579.7 0.54 SNR2 20; 21; 22; 27; 28; 34; 54

50 LMCB0540-6946 LMCRASS264 4.186 7080.5 0.76 HII 1; 2; 3; 16; 18; 25; 31; 39; 52; 53

Table 2: Catalogue of the LMC radio sources identified in the RASS. The X-ray source name (Col. 3) is taken from Pietsch et al. (in preparation). More details are given in Sect. 3

(1) (10) (11)

No. Comments

1 MC 2; MC4(0428-679); PMN J0428-6749; PKS B0428-679 S₅ from 48 used instead of S_4.75

2 MC4(0439-732A,B); PMN J0438-7310

3 MC 6; PMN J0440-6952

4 PMN J0442-6818 5

6 MC4(0446-721); PMN J0446-7205

7 MC4(0453-685); LHG 1 (W2); PMN J0453-6829 PopII?

8 N11L; DEM L34a PopI; S₅ from 28 used instead of S_4.75 9

10 PMN J0454-6800

11 N 86; MC4(0456-687); DEM L33; LHG 2 (W3); PMN J0455-6838 PopII? 12

13 QSO B0502-665

14 MC4(0506-680); LHG 11 (W10) PopI?

15 N 100; DEM L76; PMN J0506-6824

16 DEM L80; NGC 1845; PMN J0506-7026; LH26 17

18 N 103A,B; MC 22; MC4(0509-687A,B); DEM L84(85); PopI; SNR embedded in HII region;

LHG 13 (W11); NGC1850; PMN J0508-6844; IJL 34 Poor positional agreement

19 N 30; MC 25; MC4(0514-676); DEM L112(106); NGC 1871;

PMN J0513-6724; LH38; IJL 41 Star HD34632 in the field

20 N 112; MC4(0513-692A); DEM L109; IJL 39 PopI?

21 LHG 26 (W24) PopII

22 N 120A,B,C; MC 31; MC4(0519-696A,B,C); DEM L134; PopI; S_8.55 includes LMCB0518-6937;

NGC 1918; LHG 23 (W21); IJL 47; LH42; SNR embedded in HII region;

CO 17; PMN J0519-6938; PKS B0519-696 Extended complex of radio sources

23 MC4(0520-695); LHG 27 (W25); PMN J0519-6926; Sa 113 PopII?; Poor positional agreement

24 N 44I; MC4(0522-679C); DEM L156; LHG 31 (W29); LH48 SNR embedded in HII region; X-ext; Blended with HII region N 44B,C (LMCB0522-6800)

25 N 46; MC 36; DEM L162; NGC 1941; IJL 56 S₅ from 48 used instead of S_4.75

26 MC4(0524-647)

27 N 49B; MC 42; MC4(0525-660B); DEM L181; LHG 34 (W37) PopI

28 N 49A; MC 43; MC4(0525-661A); DEM L190; LH53; PopI LHG 36 (W39); PMN J0526-6604; PKS B0525-661

29 N 132D; MC 39; MC4(0525-696); DEM L186; LHG 35 (W38); PopI;

PMN J0525-6938; PKS B0525-696 SNR embedded in HII region

30 Star HD271294 in the field

31 MC 48; MC4(0528-658); DEM L204; PopII?; Radio extended;

LHG 39; PMN J0528-6550 Poor positional agreement

32 W46 Star GSC9162.0555 is in the field

33 LHG 40 (W42); PMN J0527-6911 PopI; X-ray source consists of two sources: one on soft band (star) and SNR on hard bands 34

35 Poor positional agreement

36 N 56; MC4(0532-675); LHG 48 (W53); NGC 2011; LH75 Poor positional agreement

37 N 206; MC4(0532-710B); LHG 47 (W54) PopI; SNR embedded in HII region 38

39 LHG 53 (W60) PopI?

40 MC b; MC4(0534-706); DEM L238; LHG 54 (W61); PopII? NGC 2038; PMN J0534-7034

41 MC4(0534-720); PMN J0534-7202 Poor positional agreement

42 N 63A; MC 63; MC4(0535-660); DEM L243; LHG 59 (W65); PopI;

NGC 2030; PMN J0535-6601; LH83; PKSB0535-660; IJL 73 SNR embedded in HII region

43 Star GSC8887.04000 in the field

44 N 59B; MC4(0536-675B); DEM L241; LHG 60 (W67); LH88 Poor positional agreement

45 MC d; MC4(0536-706); DEM L249; PopII? LHG 61 (W70); NGC 2056; PMN J0535-7038

46 AGN; X-var; Galaxy

47 N 157B; MC4(0538-691); PopI;

LHG 67 (W73); NGC 2060; LH99 SNR embedded in HII region

48 30 Dor; N 157A; MC 74; MC4(0539-691); DEM L263; NGC 2070; SG(X) LHG 72(W72(76,78)); PMN J0538-6905; LH100; PKS B0539-691

49 N 158A; MC 78; MC4(0540-693); DEM L269; LHG 79 (W87); PopI NGC 2081; PSR B0540-69; LH104; PKS B0540-693

50 N 159A; MC 77; MC4(0540-697A); DEM L271; LHG 78 (W84); LMC X-1; HeIII region; X-var; SNR? NGC 2079; PMN J0539-6944; LH105; CO 33; PKS B0540-697; IJL 82

Table 2: Continued

(1) (2) (3) (4) (5) (6) (7) (8) (9)

No. Radio X-Ray S_4.75 Count Rate HR 2 Type

Source Name Source Name (Jy) cts ks^-1

51 LMCB0542-6702 LMCRASS275 0.126 6.1 -0.57 snr?

52 LMCB0543-7333 LMCRASS276 0.815 8.1 BG 1; 25

53 LMCB0544-6910 LMCRASS282 9.2 -0.95 snr?

54 LMCB0544-7030 LMCRASS283 9.4 -0.05 snr?

55 LMCB0546-6416 LMCRASS292 0.232^f 231.9 bg

56 LMCB0547-6729 LMCRASS299 0.087 15.9 bg?

57 LMCB0547-6746 LMCRASS297 0.063 5.7 BG 12

58 LMCB0547-6942 LMCRASS296 0.565 36.6 SNR2 1; 5; 13; 20; 22; 27; 28; 51

59 LMCB0548-7025 LMCRASS298 0.046 116.0 -0.12 SNR3 20; 22; 27; 35

60 LMCB0550-6823 LMCRASS309 0.388 10.9 -0.29 SNR? 1; 25; 32

61 LMCB0552-6402 LMCRASS318 0.154^f 127.3 bg

62 LMCB0552-6948 LMCRASS320 0.040 32.9 bg?

63 LMCB0553-6704 LMCRASS322 2.4 bg?

64 LMCB0557-6854 LMCRASS343 0.056 5.0 ?

65 LMCB0602-6443 LMCRASS378 0.299 3.7 BG 25; 32

66 LMCB0602-6830 LMCRASS379 0.060 3.5 0.01 bg

67 LMCB0605-6625 LMCRASS390 0.065^f 3.2 0.14 bg

68 LMCB0606-7041 LMCRASS396 0.052^f 18.5 0.51 bg

69 LMCB0608-6510 LMCRASS409 0.061^f 17.4 0.10 bg

70 LMCB0611-6623 LMCRASS430 0.210 166.4 0.18 BG 38

71 LMCB0611-6734 LMCRASS429 6.6 0.23 bg

Table 2: Continued

References used in Table 2 (click here) (Col. 9), Table 4 (click here) (Col. 6) and Table 5 (click here) (Col. 7).

(1) (10) (11)

No. Comments

51 Poor positional agreement

52 MC 83; MC4(0543-735); PKS B0542-736 AGN 53 54

55 X-var; 1ES0546-642; Two Galaxies?

56 NGC 2117; PMN J0547-6728

57 MC4(0547-677); W 98; PMN J0547-6745

58 N 135; MC 89; MC4(0547-697); DEM L316; LHG 88 (W97); PopII; Position for N135 is not given in Henize (1956);

PMN J0547-6942; CO 39; PKS B0547-697 Milne et al. (1980) and Long et al. (1981) identified as N135

59 LHG 89 (W99); CO 40 PopII

60 MC 92; MC4(0550-683); DEM L328; PMN J0550-6822; PKS B0550-683 Extended radio source; Poor positional agreement

61 MC4(0550-641A); PKS B0551-640

62 MC4(0552-698); LHG 93 (W102); PMN J0552-6947 63 64

65 MC 94; MC4(0602-647); PMN J0602-6443; PKS B0602-647 Double Galaxy; S_8.4 from 32 used instead of S_8.55

66 PMN J0602-6830 Star GSC9164.1193 in the field

67 MC4(0605-664)

68 X-ext; StarGSC 9168.1191 in the field; Galaxy

69 MC4(0608-651)

70 MC4(0611-663); PKS B0611-663 S₅ from 38 used instead of S_4.75; Galaxy 71

Table 2: Continued

Abbreviations used in Col. 10.

   

(1) (2) (3) (4) (5)       (6)              (7)       (8) (9)

No. Radio X-Ray S_4.85 Count Rate HR 2 Type

Source Name Source Name (Jy) cts ks^-1

1 SMCB0034-7155 RXJ0036.9-7138 0.078^f 24.60 0.38 20

2 SMCB0035-7228 RXJ0037.3-7214 503.55 -0.95 bg? 15, 20

3 SMCB0037-7327 RXJ0038.6-7310 0.058 31.70 0.39 BG 18, 20

4 SMCB0039-7353 RXJ0041.0-7336 0.102 9.65 -0.14 SNR 18, 20

5 SMCB0040-7323 RXJ0041.9-7308 0.083 5.85 0.59 BG 18, 20

6 SMCB0043-7321 RXJ0045.1-7303 0.090 2.92 -0.19 HII 2, 20

7 SMCB0043-7330 RXJ0045.6-7313 0.039 4.19 0.13 snr? 20

8 SMCB0045-7255 RXJ0047.2-7239 0.020 2.11 1.00 BG? 15, 20

9 SMCB0045-7324 RXJ0047.6-7309 0.932 35.10 0.21 SNR 2, 7, 9, 10, 12, 15, 18, 20

10 SMCB0046-7333 RXJ0048.3-7319 0.264 3.87 0.41 SNR 2, 7, 9, 10, 12, 20

11 SMCB0047-7324 RXJ0048.9-7306 0.099 1.61 -0.21 HII 2, 20

12 SMCB0047-7332 RXJ0049.0-7314 0.070^f 12.5 0.11 SNR 8, 10, 15, 18, 20

13 SMCB0047-7343 RXJ0049.8-7324 0.046 1.40 0.68 BG 18, 20

14 SMCB0049-7338 RXJ0051.0-7321 0.046 118.10 -0.26 SNR 7, 8, 10, 15, 18, 20

15 SMCB0049-7356 RXJ0050.8-7341 0.197^f 4.77 0.41 BG 18, 20

16 SMCB0051-7254 RXJ0053.0-7239 0.196 0.96 -0.50 SNR 8, 10, 12, 15, 18, 20

17 SMCB0053-7227 RXJ0055.4-7210 0.057 24.70 0.36 BG 15, 18, 20

18 SMCB0054-7235 RXJ0056.6-7220 0.035 1.95 0.55 snr? 20

19 SMCB0057-7226 RXJ0059.5-7210 1.633 226.50 -0.08 SNR 2, 3, 9, 13, 15, 18, 19, 20

20 SMCB0058-7149 RXJ0100.3-7133 0.146 7.91 -0.34 SNR 8, 10, 18; 20

21 SMCB0058-7228 RXJ0100.7-7211 23.97 0.33 15, 20

22 SMCB0101-7226 RXJ0103.2-7209 0.125 9.05 0.35 SNR 7, 9, 10, 17, 15, 18, 20

23 SMCB0102-7218 RXJ0103.9-7202 0.411 506.03 -0.11 SNR 1, 2, 4, 7, 9, 10, 15, 18, 20

24 SMCB0103-7239 RXJ0105.0-7223 0.052 42.60 -0.32 SNR 7, 9, 10, 15, 18, 20

25 SMCB0104-7226 RXJ0105.3-7210 0.212^f 18.80 0.07 SNR 20

26 SMCB0110-7318 RXJ0111.5-7302 0.088 3.03 0.32 BG 18, 20

27 SMCB0113-7334 RXJ0114.2-7319 0.328^f 2.96 0.71 HII 2, 18, 20

Table 3: Catalogue of the SMC radio sources identified in the ROSAT PSPC. The X-ray source name (Col. 3) is taken from Kahabka et al. (in prepration). More details are given in Sect. 3

References used in Table 3 (click here) (Col. 9)

(1) (10) (11) rll

No. Comments rll rll

1 X-ray binary candidate rll

2 1E0035.4-7230; WW 13 rll

X-ray super-soft source rll

3 PMN J0038-7310 X-ray binary candidate rll

4 PMN J0040-7337; DEMS5; LI-SMC 10 rll

5 MC4 B0040-733A; PMN J0042-7306 rll

6 N 12B; NGC 249; DEMS18; LI-SMC 30 BG in X-ray classification rll

7 N 10; PMN J0044-7313; DEMS11 (14); LI-SMC 28 rll

8 PMN J0047-7239; WW 19; LI-SMC 40 rll

9 N19; S9; MC4B0045-734; PMNJ0047-7308; NGC261; DEMS32; IKT2; LI-SMC 43; WW 16; BKGS 1A SNR embeded in HII region rll

10 N 22 (20, 21, 23, 28, 28A); S10; MC4 B0046-735; DEMS37 (36); LI-SMC 45 (42) SNR embeded in HII region rll

11 N 30; S13; DEMS45 rll

12 DEMS49; IKT 5; WW 22; BKGS 2; LI-SMC 54 rll

13 N 31 (33); PMN J0049-7326; DEMS44; LI-SMC 57 (56) rll

14 PMN J0051-7321; 1E0049.4-7339; IKT 6; WW 24; LI-SMC 68 rll

15 rll

16 N 50; DEMS68; PMN J0053-7238; WW 30; BKGS 5 rll

17 MC4 B0053-724; PMN J0055-7210; NGC 306; WW 36 Two sources in MOST rll

18 N 58 (57); PMN J0056-7219; DEMS86; LI-SMC 110 (109) rll

19 N 66 (66A,B,C,D); S17; PKS B0057-724; MC4 B0057-724; PMN J0059-7210; SNR embbedded in HII region; rll

NGC 346; DEMS103; 1E0057.6-7228; IKT 18; LI-SMC 131; WW 44 Emission nebula rll

20 MC4 B0058-718B; PMN J0100-7133; DEMS108 rll

21 1E0059.0-7228; IKT 19; WW 45 X-ray binary candidate rll

22 N 76C; 1E0101.5-7226; IKT 21; WW 50; LI-SMC 160 rll

23 N 76 (76A); S20; PKS B0102-723; MC4 B0102-723; PMN J0103-7202; DEMS124 (123); SNR embeded in HII region; rll

1E0102.2-7219; IKT 22; WW 51; BKGS 12; LI-SMC 162 (161) An Oxygen-Rich Young SNR rll

24 DEMS125; 1E0103.3-7240; IKT 23; WW 52; BKGS 13; LI-SMC 169 rll

25 DEMS128; IKT 24; WW 53; BKGS 14; LI-SMC 170 rll

26 PMN J0111-7302 rll

27 N 84; S26; PKS B0113-735; MC4 B0112-736; NGC 456; Vicinity of BG source rll

PMN J0114-7318; DEMS150 (152); LI-SMC 202 (201) rll rll

Table 3: Continued

Abbreviations used in Col. 10.

3.1. Positional differences for sources in common towards the LMC

The results of the position comparison for all sources common to the Parkes radio and RASS X-ray surveys of the LMC are shown in Figs. 1 (click here)a and 1b. For the 71 sources, the mean difference in right ascension (RA) is  (radio - X-ray) with standard deviation (SD) of . The difference in declination (Dec) is  (). Figure 1b shows that there is an excess in the number of sources with small radio - X-ray differences, as expected, well above the number resulting from random coincidence.

  
Figure 1: a) The differences between radio and X-ray source positions for the LMC. Asterisks represents SNRs; filled diamonds - SNRs embedded in HII regions; open circles - background sources; filled square - HII regions and triangles - unclassified sources. Further details are given in Sect. 3.1. The dashed circle is   radius. b) The number of sources as a function of radio - X-ray source separation towards the LMC per unit area of the radial bin (per arcmin²)

Dividing this sample into (i) SNRs, (ii) SNRs embedded in HII regions and (iii) background sources, and again comparing radio - X-ray source positions we obtain:  and  for 19 SNRs;  and  for 17 SNRs embedded in HII regions, and  and  for 27 background sources. There are two HII regions and six unclassified sources.

Clearly, there is a large RA positional difference for SNRs embedded in HII, regions and the nature of this difference is the subject of further investigation. Excluding the embedded SNRs and source LMCB0540-6946 (LMC X-1; see Sect. 4.6), the positional alignment of the Parkes radio and RASS surveys is good with differences of ,  (radio ), with standard deviations in the differences of  and  respectively.

This uncertainty is consistent with the combined positional uncertainties for the radio and the X-ray sources, and retrospectively justifies the initial identification criteria of 2.5 (which is equivalent to 3.4 in RA and 4.1 in Dec).

3.2. Positional differences for sources in common towards the SMC

We have compared the positions for all 27 sources common to radio and X-ray surveys of the SMC. We used the same criterion for source identification as that used for the LMC survey, i.e., the source must lie within 2.5 of its counterpart. This criterion was chosen according to the upper limit of positional uncertainties at our 1.42 GHz survey. These positions were compared with X-ray positions from Kahabka et al. (in preparation).

The results of this comparison are shown in Fig. 2 (click here). For the 27 sources, the mean difference in RA is ) and in Dec is ). Thus, we have found no significant positional bias between our radio positions and those from the ROSAT PSPC surveys.

  
Figure 2: The differences between radio and X-ray source positions for the SMC. Asterisks represents SNRs; open circles - background sources; filled square - HII regions and triangles - unclassified sources. The dashed circle is 1  radius