The identification of the LMC radio/X-ray object 0540-69.3 with an optical nebulosity associated with a supernova remnant is reported. The optical component was found in a search conducted with the 3.9-m Anglo-Australian Telescope in the direct imaging mode in H beta, the forbidden O III line at 5007 A, the forbidden N II line at 6584 A and the continuum at 5323 A. An intense circular source of forbidden O III emission was discovered, along with a larger weaker arc of forbidden O III which together surround the radio source. No H beta emission was detected; however, a faint annulus coincident with the intense oxygen feature was found in forbidden N II. Spectroscopic analysis of the O III features indicates the annulus to have a velocity dispersion around 3000 km/sec, characteristic of a very young supernova remnant, while the arc is most likely background emission from the photoionized nebula.
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Mathewson et al. (1980) studied this question.