Unexpected gamma ray emissions by classical novae

Non classé

An international team of scientists, including researchers1 of French laboratories like the Institut de recherche en astrophysique et planétologie of Toulouse (CNRS/CNES/Université Paul Sabatier-Toulouse III) and the Laboratoire physique subatomique et cosmologie of Grenoble (CNRS/UJF/Grenoble INP), detected for the first time a gamma photon emission from three so-called classical novae, using the Fermi LAT telescope observatory (NASA). Such an emission of gamma radiation in a classical nova is a startling discovery that will provide information about the acceleration mechanisms within these objects and led to the identification of a new class of high-energy gamma emitters.

In 2010, the same collaboration had observed a high energy gamma-ray emission (2) from a symbiotic nova (v407 Cyg, Abdo et al., 2010) just as surprising. It then proposed a possible explanation lying on mechanisms specific to this kind of nova. With these new observations, the Fermi collaboration again confronts a surprising phenomenon of gamma-ray emission but this time coming from classical novae.

Classical novae are thermonuclear explosion phenomena occurring at the surface of a white dwarf that accretes matter from a main-sequence star in a very tight binary system. Symbiotic novae differ from classical novae in that they involve a red giant star rather than a main sequence star. In the last case, the gamma ray emission could result from the presence of accelerated particles in the shock between the ejecta and the dense wind of the secondary star. In the case of classical novae, secondary stars do not emit dense wind, which again raises the problem of the origin of the gamma ray emission. So this interesting result should lead us to better understand the acceleration mechanisms that occur in these objects.

Among the hypotheses considered, the one which assumes the existence of internal shocks in the envelope of the nova – which would accelerate the particles to relativistic speeds – seems favored. The nature of the high-energy particles (protons or electrons) which are at the origin of the gamma ray emission is not yet determined, the spectral analysis allowing the two types of particles at the origin of the observed radiation.

The gamma ray emissions of these four novae (the three classical ones and the symbiotic one) (3) are relatively similar. They have been detected for about twenty days. These observations suggest that all novae are emitting gamma photons of high energy during their explosion.

Note(s): 

  • 1 The Fermi collaboration includes the NASA and the DOE on the American side and institutes from six countries (USA, France, Italy, Japan, Sweden and Germany). Regarding the French participation, teams are associated with the CNRS-IN2P3, the INSU and the CEA-IRFU. Pierre Jean, CNRS researcher at the IRAP (CNRS / CNES / Toulouse III-Paul Sabatier University) is a lead author of this publication.
  • 2 Energy higher than 100 MeV.
  • 3 less than 4500 Parsec, i.e., 15 light-years.

Sources : 

IRAP Contact :

  • Pierre Jean, pierre.jean@irap.omp.eu

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