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The role of classical novae as potential gamma-ray emitters is reviewed, on the basis of theoretical models of the gamma-ray emission from different nova types. The interpretation of the up to now negative results of the gamma-ray observations of novae, as well as the prospects for detectability with future instruments (specially onboard INTEGRAL) are also discussed. [ABSTRACT FROM AUTHOR]

The mechanism of classical novae explosions is explained, together with some of their observational properties. The scarce but not null impact of novae in the chemical evolution of the Milky Way is analyzed, as well as their relevance for the radioactivity in the Galaxy. A special emphasis is given to the predicted gamma-ray emission from novae and its relationship with the thermonuclear model itself and its related nucleosynthesis. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

New results concerning the synthesis of radioactive nuclei in classical nova explosions are presented, together with their influence on the gamma-ray emission from these objects and the prospects for the detectability with present and future instruments. The isotopes involved in gamma-ray emission from classical novae are [sup 13]N, [sup 18]F, [sup 7]Be, [sup 22]Na and [sup 26]Al. Both [sup 13]N and [sup 18]F are crucial for the short duration annihilation emission, at 511 keV and below, that is emitted during the first hours after the outburst, before the nova maximum in visual magnitude. New recent results concerning the nuclear reaction rates involved in [sup 18]F destruction have been incorporated into our hydrodynamic code, which models the nova explosion with a detailed follow up of the associated nucleosynthesis. As a result of the larger rates of [sup 18]F destruction through proton captures, this isotope is produced in smaller quantities (typically by a factor of 10), leading to smaller fluxes in the 30–511 keV range. Concerning the medium and long lived isotopes, the inclusion of the latest reaction rates available in the NeNa-MgAl cycles provides an enhanced [sup 22]Na production with respect to previous results, leading to a larger 1275 keV flux emitted through its decay. [sup 26]Al is practically unchanged. The implications of our new results for the observability of novae by CGRO and by the future INTEGRAL instruments are addressed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Detection of gamma-ray emission from classical novae, in the range between 30 and 511 keV, would provide a crucial test of the thermonuclear runaway (TNR) model. This emission results from the annihilation of positrons, emitted by some radioactive nuclei ([sup 13]N and [sup 18]F) synthesized during the TNR; it has a short duration and is produced before the optical maximum. Therefore, it can only be analyzed “a posteriori,” once the nova has been discovered optically. The capability to observe all the sky, together with its high sensitivity in the low-energy range, make BATSE an ideal instrument to detect this emission. Data analysis techniques previously applied for BATSE observations of 511 keV transients of short duration have been used. The first results from the systematic search in BATSE background data which is under way are presented, which include nearby novae that have exploded since CGRO launch. Comparison with recent updated theoretical models is made in each case. Although no positive detection has been obtained up to now, upper limits to the emitted flux are presented. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]