The opening line of The Bell Jar gives a clear indication of the period in which the novel is set: the Rosenbergs were executed by electrocution on 19 June 1953. It is also the first indication that the novel is to be highly autobiographical: Sylvia Plath spent June 1953 in New York as guest editor on Mademoiselle, a monthly magazine for young women.
Julius and Ethel Rosenberg were American communists convicted in March 1951 of espionage – specifically, of passing information about the atomic bomb to the Russians. They were sentenced to death on 5 April 1951, although it was over two years before the sentence was carried out. In the intervening period, legal appeals were made against the conviction, as well as pleas for clemency from high-profile figures including Pope Pius XII and Pablo Picasso.
Death by electrocution, or 'the electric chair', is one of the most barbaric forms of state-sponsored execution. It has now been outlawed in most American states. Execution is now generally by lethal injection, although there are still some states where electrocution remains an option should the condemned person request it.