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New Hubble Space Telescope Observations of High-Velocity Lyα and Hα in SNR 1987A

We describe and model high-velocity (≈ 15,000 km s-1) Lyα and Hα emission from the supernova remnant SNR 1987A seen in 1997 September and October with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ≈ 75% of the radius of the inner boundary of the inner circumstellar ring and confined within ±30° of the equatorial plane. Departure from axisymmetry in the Lyα and Hα emission correlates with that seen in nonthermal radio emission and reveals an asymmetry in the circumstellar gas distribution. We also see diffuse high-velocity Lyα emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.