The penultimate supernova in the Large Magellanic Cloud - SNR 0540-69.3

We present spectra of the supernova remnant (SNR) 0540-69.3 in the Large Magellanic Cloud that cover the wavelength interval 3500-9800 A. An optical continuum is observed over this entire wavelength range from synchrotron emission near the 50 ms pulsar inside the remnant. The spectrum contains emission lines which are shifted by +370 km s^-1^ from the local LMC rest velocity. The line widths average 2735 + 200 km s^-1^ (FWZI), which indicates an expansion age of 762 +/- 50 yr. We detect lines of [O I], [O II], [O III], [S II]. [S III], [Ar III], [Ni II], [Fe II], [Fe III], Hα, and possibly [Fe V] and [Fe VII]. The Hα identification differs from the suggestion of Ca I] made by previous workers. The strong lines of oxygen and sulfur are similar to those seen in Cas A, the remnant of a massive star. Iron and nickel mixed into the oxygen-rich zone emulate properties inferred for SN 1987A, while a pulsar inside the SNR resembles the Crab Nebula. It is very likely that 0540-69.3 is the young SNR following core collapse of a massive star akin to the progenitor of SN 1987A. Since the explosion took place less than 1000 yr before 1987A, this object may be its most recent predecessor in the LMC.