Abstract.
Classical novae produce radioactive nuclei which are emitters of γ-rays in the MeV range.
Some examples are the lines at 478 and
1275 keV (from 7Be and 22Na and the positron-electron annihilation emission (511 keV line and a continuum below this energy,
with a cut-off at 20-30 keV). The analysis of γ-ray spectra and light curves is potentially a unique and powerful tool both to trace the
corresponding isotopes and to give insights on the properties of the expanding envelope determining its transparency. Another possible origin
of γ-rays is the acceleration of particles up to very high energies, so that either neutral pions or inverse Compton processes produce
γ-rays of energies larger than 100 MeV. MeV photons during nova explosions have not been detected yet, although several attempts
have been made in the last decades; on the other hand, GeV photons from novae have been detected in some particular novae, in symbiotic binaries,
where the companion is a red giant with a wind, instead of a main sequence star
as in the cataclysmic variables hosting classical novae. Both mechanisms of γ-ray production in
novae are reviewed, with more emphasis on the one related to radioactivities.
Keywords: stars: novae, cataclysmic variables -- white dwarfs -- gamma-rays: observations -- instrumentation: miscellaneous