2015ApJ...801L..16F

We present new Hubble Space Telescope images of high-velocity Hα and Lyα emission in the outer debris of SN 1987 A. The Hα images are dominated by emission from hydrogen atoms crossing the reverse shock (RS). For the first time we observe emission from the RS surface well above and below the equatorial ring (ER), suggesting a bipolar or conical structure perpendicular to the ring plane. Using the Hα imaging, we measure the mass flux of hydrogen atoms crossing the RS front, in the velocity intervals (-7500 < V_obs< -2800 km/s) and (1000 < V_obs< 7500 km/s), (1000 < V_obs < 7500 km/s), {dot}M_H = 1.2x10^–3 M_☉/yr. We also present the first Lyα imaging of the whole remnant and new Chandra X-ray observations. Comparing the spatial distribution of the Lyα and X-ray emission, we observe that the majority of the high-velocity Lyα emission originates interior to the ER. The observed Lyα/Hα photon ratio, (R(L_α/H_α)) ≈ 17, is significantly higher than the theoretically predicted ratio of ≈5 for neutral atoms crossing the RS front. We attribute this excess to Lyα emission produced by X-ray heating of the outer debris. The spatial orientation of the Lyα and X-ray emission suggests that X-ray heating of the outer debris is the dominant Lyα production mechanism in SN 1987 A at this phase in its evolution.