Discovery of Optical Echoes from Supernova 1987A: New Probes of the Large Magellanic Cloud

Coronagraphic observations of SN 1987A have revealed the first "light echo" or transient reflection nebula due to light from a supernova. Two echoes from dust 400 and 980 lt-yr in front of SN 1987A were discovered on UT 1988 March 4.05. These phenomena can be exploited to probe the physics of the dust, the structure of the interstellar medium, the unobserved initial hours of SN 1987A, and the relation between gasdynamics and star formation in an active portion of the Large Magellanic Cloud. The results show that the dust scatters consistent with Rayleigh's law, that at least some of the light echo is reflected from the N157C "superbubble" nebula, and that future "reobservation" of the time evolution of the ultraviolet light pulse associated with the shock outbreak through the progenitor star's surface may be difficult to resolve. A scheme is presented for using the echo to map out the full three-component motions and positions of the dust clouds, as well as detailed information about the gas clouds and stars in the vicinity of the echo.