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Twenty years after the explosion of SN 1987A, we are now able to observe thethree-dimensional spatially resolved inner ejecta. Detailed mapping of newlysynthesised material and its radioactive decay daughter products sheds light onthe explosion mechanism. This may reveal the geometry of the explosion and itsconnection to the equatorial ring and the outer rings around SN 1987A. We haveused integral field spectroscopy to image the supernova ejecta and theequatorial ring in the emission lines of [Si I]+[Fe II] and He I. The spectralinformation can be mapped into a radial velocity image revealing the expansionof the ejecta both as projected onto the sky and perpendicular to the skyplane. The inner ejecta are spatially resolved in a North-South direction andare clearly asymmetric. We argue that the bulk of the ejecta is situated in thesame plane as defined by the equatorial ring and does not form a bipolarstructure as has been suggested. The exact shape of the ejecta is modelled andwe find that an elongated triaxial ellipsoid fits the observations best. Fromour spectral analyses of the ejecta spectrum we find that most of the He I, [SiI] and [Fe I-II] emission originates in the core material which has undergoneexplosive nucleosynthesis. The He I emission may be the result of alpha-richfreeze-out if the positron energy is deposited locally. Our observationsclearly indicate a non-symmetric explosion mechanism for SN 1987A. Theelongation and velocity asymmetries point towards a large-scale spatialnon-spherical distribution as predicted in recent explosion models. Theorientation of the ejecta in the plane of the equatorial ring argues against ajet-induced explosion through the poles due to stellar rotation.

The 3-D Structure of SN 1987A's inner Ejecta