“…0 found by Fahlman and Gregory (1981 (Gregory, 1982 (Tuohy and Garmire, 1980;Lamb and Markert, 1981;Becker et al , 1982;Helfand, 1980Helfand, , 1981 Becker et al (1982), who found the x-ray emission (cf. also van (Large, 1971: Guseinov andKasumov, 1978;Gailly, Lequeux, and Masnou, 1978;Chevalier, 1981;Lyne, 1982), with a brief interruption (Taylor, 1977) Panagia (1978, 1980) Cas A (Chevalier, 1981) was, at least, not the product of a normally bright SN. Chevalier attributes it to a very massive star that 1ost its hydrogen-rich envelope before being disrupted, perhaps by an electron-positron pair production supernova (Sec.…”