Superradiance and stimulated scattering in SNR 1987A

Abstract

The rings observed around supernova remnant 1987A are emitted by a plasma mainly made of ionized and neutral hydrogen atoms. With a density of 10 power 10 atoms per cubic metre, and at least a dimension of plasma of 0.01 light-year, the column density is 10 power 24 atoms per square metre, much more than needed for an optically thick gas at Lyman frequencies (Case B). While, at 10000 K, the bulky gas would absorb Lyman lines fully, at 50000K it emits superradiant lines. As superradiance de-excites the atoms strongly, nearly all available energy is emitted in a few competing modes: Superradiance appears only for beams which cross the largest column densities; for an observation from Earth, these beams generate three elliptical hollow cylinders whose bases are the observed rings; admitting that the Earth is not in a privileged direction, these cylinders envelope ellipsoidal shells observed, for the external rings, by photon echoes. For the equatorial ring, the brightness of the superradiant beams is multiplied by a quasi-resonant induced scattering of the rays emitted by the star. The de-excitation of atoms by emitted beams cools the gas strongly, so that ionization decreases fast, the process self accelerates. The energy of the high radiance rays from the star is strongly scattered to the ring while the low radiance of the glow which surrounds the star is rather amplified. The fast absorption of the radial beams produces the radial decrease of radiance of the ring while a competition of modes produces the pearls.