Pre-Supernova Ring Around PSR0540-69
  SNR0540-69 is a supernova remnant in the LMC, harbouring a young (~1600 yrs) radio/optical/X-ray pulsar (P=50 ms). Ground based Halpha imaging of the region has shown a unique spiral-like structure centered around the pulsar. In narrow band HST imaging, the feature seems resolved in a ring-like structure, probably ejected by the progenitor star in a pre-supernova phase (> 10^4 yrs ago). 
Patrizia A. Caraveo (Istituto di Fisica Cosmica del CNR, Milano,   Italy, also Istituto Astronomico, Roma, Italy), Roberto M...