1. Introduction

The MCs have recently been surveyed systematically at radio frequencies with the Parkes telescope (Haynes et al. 1991). Also, complete MOST surveys at 843 MHz of both Clouds are in preparation and some results are presented in Mills et al. (1984), Ye (1988) and Ye & Turtle (1993).

Using the Parkes telescope observations, we have derived catalogues of radio sources in the MCs (Filipovic et al. 1995, 1996, 1997). A total of 483 sources towards the Large Magellanic Cloud (LMC) and 224 towards the SMC have been detected at at least one radio frequency (Filipovic et al. 1998a). Most of the MCs sources have been classified in one of three groups: SNRs, H II regions or background sources. In total, 209 radio sources in the LMC and 37 sources in the SMC are classified to be either H II regions or SNRs. About 60 SNRs and SNR candidates in the LMC and 20 in the SMC have been identified in recent studies of Filipovic et al. (1998a) and Ye (1988). Of these, there are 23 SNR candidates in the LMC and 6 in the SMC which need to be confirmed as SNRs. These large numbers of SNRs and SNR candidates in the MCs are sufficient to start a study of their physical properties.

However, in Parkes surveys we could not resolve any of these sources due to the relatively low angular resolution (at the best ∼3' at 8.55 GHz). This resolution problem can be overcome using the Australia Telescope Compact Array (ATCA).

Therefore, our aims were twofold:

1. To observe a complete sample of H II regions, SNRs and SNR candidates from the MCs using the ATCA at two radio frequencies (4.79 and 8.64 GHz).
2. To use this data base in conjunction with data from other frequencies, such as existing ATCA mosaic surveys at 1.4/2.3 GHz, and the MOST survey at 843 MHz to investigate the physical properties of those objects in the MCs.

2. Observations

2.1. The ATCA Mosaic Observations of the Magellanic Clouds

2.2. The ATCA Pointed Observations of Selected Objects in the Magellanic Clouds

The aim was to image a large number of H II regions, SNRs and SNR candidates in snapshot mode. The tradeoff of image complexity with uv coverage indicates this compromise of resolution is justified. The ``largest well-imaged structure'' with snap-shots distributed over hour angle for the 375 m array is around 200" and the flux sensitivity better than 0.2 mJy. The strongest confusing background source is around 2 mJy and with cuts distributed well in hour angle, the confusion limit approach the noise level. The preliminary data reduction from our pilot observations confirmed our expectations of the ATCA to do this type of work.

Using this method we observed, so far, all SNRs and SNR candidates in both Clouds (∼80). Observations were undertaken during eight observing days in 1997.

3. Results

In Figs. 2a and 2b we present preliminary results from the study of SNR N 76. Both images are taken with the ATCA in ``snap-shot'' mode at λ=6 and 3 cm. SNR N 76 (also known as DEM S123 and SMC B0102-7218) is located in the SMC and previously has been classified as SNR candidate. Here, we can clearly see a shell-like structure - a typical SNR characteristic. With a radio spectral index of α = -0.33±0.19 we classify this source as a firm SNR. Some ∼3' north-west from N 76 is the source RX J0104.0-7201 which has been previously classified as a background object (Ye 1988). In our image in Fig. 2b, we can clearly resolve this source at λ=3 cm (resolution 15"). The radio spectral index of this source is α = -0.65±0.11. Therefore, we classify this source as a SNR candidate and further high resolution studies with the ATCA's longer baselines (6 km) are necessary.

A general SNR-like morphology was clearly detected in all other observed SNR objects. Typical ``shell-like'' structure can be seen in the majority of SNR candidates that were observed. These preliminary results justify our initial expectation and intentions.

Sixteen SNRs in the LMC and four in the SMC have also been observed with the ATCA (Dickel & Milne 1994; Amy 1994). We intend to make use of their results as a part of this study.

4. Future Work

In addition, individual SNRs will be studied in more detail. Some of their characteristics may be related to peculiar properties of the interstellar medium around the explosion site and/or different precursor stars. Theoretical models indicate that changes in density, clumpiness and other properties of the surrounding medium can have a significant effect upon the evolution of an SNR and its emission. However, the collective properties of the SNRs in the MCs studied to date are surprisingly consistent and quite similar to the population of Galactic SNRs (Dickel & Milne 1994), despite major differences between these galaxies.

References

• Amy S.W., 1994, Proc. ASA 11, 83
• Dickel J.R., Milne D.K., 1994, Proc. ASA 11, 99
• Filipovic M.D., Haynes R.F., White G.L., et al., 1995, A&AS 111, 311
• Filipovic M.D., White G.L., Haynes R.F., et al., 1996, A&AS 120, 77
• Filipovic M.D., Jones P.A., White G.L., et al., 1997, A&AS 121, 321
• Filipovic M.D., Haynes R.F., White G.L., Jones P.A., 1998a, A&AS (in press)
• Filipovic M.D., Pietsch W., Haynes R.F., et al., 1998b, A&AS 127, 119
• Haynes R.F., Klein U., Wayte S.R., et al., 1991, A&A 252, 475
• Kim S., Staveley-Smith L., Dopita M.A., et al., 1998, ApJ 503, 674
• Mills B.Y., Turtle A.J., Little A.G., Durdin M.J., 1984, Aust. J. Phys. 37, 321
• Staveley-Smith L., Sault R.J., Hatzidimitriou D., Kesteven M.J., McConnell D., 1997, MNRAS 289, 225
• Ye T., 1988, PhD Thesis, Sydney University
• Ye T., Turtle A.J., 1993, In: Lecture Notes in Physics 416, New Aspects of Magellanic Cloud Research, eds. Baschek B., Klare G., Lequeux J., p. 167

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