The prompt gamma-ray emission of novae

Classical novae are potential gamma-ray emitters, because of the disintegration of some radioactive nuclei synthesized during the explosion. Some short-lived isotopes (such as (13)N and (18)F), as well as the medium-lived (22)Na, decay emitting positrons, which annihilate with electrons and thus are responsible for the prompt emission of gamma-rays from novae. This emission consists of a 511 keV line plus a continuum between 20 and 511 keV and is released before the maximum in visual luminosity, i.e., before the discovery of the nova. The main characteristics of this prompt emission, together with the related uncertainties (both of nuclear and hydrodynamical origin, with a particular emphasis on the influence of the envelope properties) and prospects for delectability are analyzed in this paper. (C) 2002 Elsevier Science B.V. All rights reserved.