Exploring the Central Region of SNR 0540-69.3 with JWST. I. Three-dimensional Morphology

Abstract The young supernova remnant SNR 0540-69.3 in the Large Magellanic Cloud offers a detailed view of an energetic pulsar-wind nebula (PWN) interacting with the surrounding ejecta. We present infrared observations of the central region of SNR 0540-69.3 obtained with the JWST NIRSpec and Medium-Resolution Spectrometer integral field units. From the observations we reconstruct the 3D morphology of the strongest emission lines in the inner ejecta (≲1000 km s −1 ), which reveal the distributions of H I , He I , [Ne ii ], [Ne iii ], [S iii ], [S iv ], [Fe ii ], and [Ni II ]. The 3D morphology of most lines is dominated by two highly fragmented lobes of approximately similar size. Based on the assumption that the lobes are symmetric around the pulsar, we infer a pulsar kick velocity of ∼300 km s −1 away from the observer. There are differences in the 3D morphologies of individual emission lines due to a combination of varying physical conditions and abundances. The detection of H i 1.8756 μ m in the inner ejecta confirms the classification of the supernova as a Type II and shows that hydrogen was mixed down to low velocities of <400 km s −1 in the explosion. We compare the results to the Crab Nebula and conclude that asymmetries originating in the explosion most likely play a major role in shaping these PWNe.