A team of researchers, including scientists from the Institut de recherche en astrophysique et planétologie in Toulouse (CNRS / Université Paul Sabatier, Observatoire Midi-Pyrénées), discovered a low energy (1) gamma ray emission coming from the Type Ia supernova SN2014J by analyzing the observations made by the SPI spectrometer and the ISGRI / IBIS imager INTEGRAL space observatory (International Gamma-Ray Laboratory of the European Space Agency). This is the first time that such a radiation is observed from this type of supernova.
The SN2014J supernova was discovered in optics on January 21, 2014 in the galaxy M82, at a distance of 3.5 megaparsec (2). It was quickly identified as a Type Ia supernova, issued from the thermonuclear explosion of a white dwarf in a close binary system. This is the closest supernova of type Ia detected in almost 40 years.
By analyzing the data acquired by the INTEGRAL observatory between 50 and 100 days after the explosion, the researchers observed nuclear gamma rays at 847 keV and 1238 keV which are the signature of the radioactive decay of 56Co nuclei whose half-life is 77 days. This observation is direct evidence of the nucleosynthesis production of a significant amount of 56Ni nuclei during the explosion of the star. The 56Ni decreases rapidly, with a half-life of 6 days, into 56Co, which in turn decreases into iron core (56Fe) by emitting the nuclear gamma rays observed. The INTEGRAL observatory also detected the gamma (continuum) emission due to the Compton scattering of these gamma rays with the expanding matter.
The observations made by INTEGRAL suggest that a mass of 0.6 solar mass of radioactive 56Ni was synthesized during the explosion. The spectral analysis of gamma rays were used to estimate the speed of the ejecta to about 10000 km/s. The properties of the observed radiation are consistent with a scenario according to which a massive white dwarf exploded after it had accreted enough matter from a companion star to become gravitationally unstable. It is however not possible to exclude scenarios which suggest that this type of supernova is due to the merger of two white dwarfs.
Depending on the nucleosynthesis odels, supernova explosions are the main source of iron in the Universe. The observations made by INTEGRAL have now confirmed this hypothesis. They also provide valuable information to understand the physics of the explosion of the supernovae of type Ia.
1 photons between 100 keV and 10 MeV
2 11.5 millions light-years
- Article : “Cobalt-56 gamma-ray emission lines from the type Ia supernova 2014J“, Churazov et al., Nature, 28 Août 2014.
- CNRS-INSU Press Release : http://www.insu.cnrs.fr/node/4973
- ESA Press Release : http://www.esa.int/Our_Activities/Space_Science/Integral_catches_dead_star_exploding_in_a_blaze_of_glory
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