Uncovering a supernova remnant hidden near LMC X-1

In a kinematic study of LMC Hn regions, we serendipitously found a fast-expanding (velocity offsets up to similar to 200 km s(-1)) shell in the northern lobe of the luminous H II region N159. The expansion pattern and the [S II]/H alpha ratio of the shell are consistent with those seen in supernova remnants (SNRs). Confirmation of this SNR candidate in radio and X-ray wavelengths has been hampered by thermal emission of the luminous H II region N159 itself and scattered X rays from the nearby luminous source LMC X-1. Recent ROSAT observations finally resolved N159 from LMC X-1, thus confirming the identification of this as a newly identified SNR, which we designate as SNR 0540-697.