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Cobalt-56 γ-ray emission lines from the type Ia supernova 2014J


A type Ia supernova is thought to be a thermonuclear explosion of either a single carbon–oxygen white dwarf or a pair of merging white dwarfs. The explosion fuses a large amount of radioactive 56Ni (refs 1–3). After the explosion, the decay chain from 56Ni to 56Co to 56Fe generates γ-ray photons, which are reprocessed in the expanding ejecta and give rise to powerful optical emission. Here we report the detection of 56Co lines at energies of 847 and 1,238 kiloelectronvolts and a γ-ray continuum in the 200–400 kiloelectronvolt band from the type Ia supernova 2014J in the nearby galaxy M82. The line fluxes suggest that about 0.6 ± 0.1 solar masses of radioactive 56Ni were synthesized during the explosion. The line broadening gives a characteristic mass-weighted ejecta expansion velocity of 10,000 ± 3,000 kilometres per second. The observed γ-ray properties are in broad agreement with the canonical model of an explosion of a white dwarf just massive enough to be unstable to gravitational collapse, but do not exclude merger scenarios that fuse comparable amounts of 56Ni.

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Figure 1: Gamma-ray lines from Co decay at 847 and 1,238 keV in the spectrum of SN 2014J.
Figure 2: Signatures of 56Co lines at 847 and 1,238 keV in SPI images.
Figure 3: Appearance of a new hard (100–600 keV) X-ray source at the position of SN 2014J.
Figure 4: Broadening of the 847 and 1,238 keV lines.

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This work was based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the principal investigator countries: Denmark, France, Germany, Italy, Switzerland and Spain) and with the participation of Russia and the United States. We are grateful to the ESA INTEGRAL team and E. Kuulkers for their prompt reaction to the SN 2014J event. E.C., R.S. and S.G. wish to thank the Russian INTEGRAL advisory committee for allocating an additional 106 s of time from a regular programme to SN 2014J observations. R.S., S.G. and S.S. are partly supported by grant no. 14-22-00271 from the Russian Scientific Foundation. J.I. is supported by MINECO-FEDER and Generalitat de Catalunya grants. The SPI project has been completed under the responsibility and leadership of CNES, France. ISGRI has been realized by CEA with the support of CNES. We thank P. Höflich, K. Nomoto and S. Woosley for making available their supernova explosion models HED6, W7 and DD4.

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Authors and Affiliations



E.C.: reduction and modelling of the INTEGRAL observations, simulations of the emerging γ-ray emission, interpretation, manuscript preparation; R.S.: principal investigator of one of the observations, observation planning, interpretation and manuscript preparation; J.I.: principal investigator of one of the observation proposals, observation planning, modelling of observations, interpretation and manuscript preparation; J.K.: reduction and analysis of SPI data, manuscript review; P.J.: reduction and spectral analysis of SPI observations, manuscript review; F.L.: reduction of the IBIS/ISGRI observations, manuscript preparation; N.C.: determination of 56Ni mass from the optical data, manuscript review; S.G.: reduction of the IBIS/ISGRI observations, manuscript review; E.B.: theoretical modelling, manuscript review; S.S.: principal investigator of the M82 observations, manuscript review; M.R.: reduction of the IBIS/ISGRI observations, manuscript review.

Corresponding author

Correspondence to E. Churazov.

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Extended data figures and tables

Extended Data Figure 1 Variations in the particle background during INTEGRAL observations.

Anti-coincidence-system count rate is shown as a function of time, expressed through the revolution number. One revolution lasts about 3 days. Periods of very high and variable background (shown in blue) due to solar flares were omitted from the analysis. Periods of quiescent background (red) were used to derive the spectrum of SN 2014J.

Extended Data Figure 2 Comparison of the SPI background spectrum and the expected type Ia supernova emission.

Typical quiescent background (black) and supernova model (red, convolved with SPI energy resolution) spectra.

Extended Data Figure 3 Predicted spectra for days 50, 75 and 100 after explosion.

The 3PAR model spectrum calculated for day 75 is used for comparison with the INTEGRAL data obtained between day 50 and 100 since the explosion. Weak lines below 200 keV correspond to 56Ni (day 50) and 57Co (day 100).

Extended Data Figure 4 Contributions of various components to the model spectrum.

The lines are formed by γ-rays escaping the ejecta without interactions. The low-energy tail of each line is due to Compton down-scattering of the photons because of the recoil effect. The ‘humps’ in the tails correspond to the scattering by 180°. The magenta line shows the contribution of the ortho-positronium annihilation. Annihilation of para-positronium contributes to 511 keV line.

Extended Data Figure 5 Confidence contours for our three-parameter model.

The cross shows the best-fit values. Contours are plotted at Δχ2 = 1 with respect to the best-fit value and characterize the 1 s.d. confidence interval for a single parameter of interest.

Extended Data Table 1 Parameters of the observed gamma-ray lines of 56Co
Extended Data Table 2 Comparison of typical type Ia supernova explosion models with the data

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Churazov, E., Sunyaev, R., Isern, J. et al. Cobalt-56 γ-ray emission lines from the type Ia supernova 2014J. Nature 512, 406–408 (2014).

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