The Study Of γ-Ray Sources In Novae

The symbiotic recurrent nova V407 Cyg is the first nova detected by Fermi/LAT in2010 at ≥ 100 MeV γ-ray emissions. subsequently, there are another four classical novae and one symbiotic recurrent nova detected by the same telescope at γ-rays. Due to the dense ambient medium formed by the thick stellar wind from red giants, the symbiotic recurrent novae are well explained by the diffusive shock acceleration(DSA) mechanism.Unfortunately, there are not the dense ambient medium in classical novae like symbiotic recurrent novae. The γ-ray emissions from classical novae are still under debate.Considering that the spectra properties of the observed classical novae are very similar to the symbiotic recurrent novae at γ-rays, and the observational fact that not all classical nova can generate γ-rays, we think they have the same mechanism to generateγ-rays. In this paper, we investigate the interplay between novae ejecta and accretion disks around white dwarfs or circumbinary(CB) disks surrounding nova systems. After discussing the donors, the accretion disks and the CB disks, we suggest that the interplay between novae ejecta and CB disks is most probable to produce γ-rays.We calculate a grid model to discuss the γ-ray sources in classical novae, and find that the mass of white dwarf and the orbit period in classical novae can greatly affect the production of γ-rays. Using our grid model and synthesis population method, we estimate that about 18% of classical novae can produce γ-rays, and the occurrence rate of γ-ray classical novae is about 9.7 yr-1in the Galaxy.