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A Nova Source of Gamma Rays
Novae are thermonuclear explosions that occur at the surface of a white dwarf when material is pulled onto it from a companion star in a binary system. They are different from supernovae because the explosion does not completely destroy the white dwarf. Novae have not been widely considered as high-energy gamma-ray sources. Using the Fermi Large Area Telescope, Abdo et al. (p. 817) now report the detection of a nova explosion in gamma rays. The observations provide evidence for the acceleration to relativistic energies of particles in the shock wave following the explosion.
Abstract
Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable γ-ray emission (0.1 to 10 billion electron volts) from the recently detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary and that particles can be accelerated effectively to produce π0 decay γ-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.
