Abstract
The luminosity of stripped-envelope supernovae, a common type of stellar explosion, is believed to be mainly driven by the radioactive decay of the nickel synthesized in the explosion and carried in its ejecta. Additional possible energy sources have been previously suggested1,2,3,4,5, in which the two most observationally based results have been from a comparison of the observed time-weighted luminosity with the inferred radioactive power1 and from a comparison of the light curves with particular theoretical models3. However, the former result1 was not statistically significant, and the latter3 is highly dependent on the specific models assumed. Here we analyse the energy budget of a sample of 54 well-observed stripped-envelope supernovae of all sub-types and present statistically significant, largely model-independent, observational evidence for a non-radioactive power source in most of them (and possibly in all). We consider various energy sources, or alternatively, plausible systematic errors, that could drive this result, and conclude that the most likely option is the existence of a long-lived central engine, operating over ≈103–106 s after the explosion. We infer, from the observations, constraints on the engine properties. If, for example, the central engine is a magnetized neutron star, then the initial magnetic field is ≈1015 G and the initial rotation period is 1–100 ms, suggesting that stripped-envelope supernovae may constitute the formation events of the objects known as magnetars.
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Data availability
The data used to create the figures in this study, as well as the scripts used to generate the figures, are available online in Zenodo (https://doi.org/10.5281/zenodo.10550304). Source data are provided with this paper.
Code availability
We used Python 3.7.6 and the public Python packages NumPy 1.19.4, Matplotlib 3.4.1 and Pillow 7.0.0. The stellar-evolution code MESA is freely available and documented at https://docs.mesastar.org/en/release-r23.05.1/.
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Acknowledgements
We thank A. Sharon, D. Kushnir and A. Gilkis for their comments and discussions. This work was supported by grant nos. 818899 (E.N.) and 833031 (D.M.) from the European Research Council.
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Ó.R. and E.N. conceived the idea of measuring the Katz integral for these data. Ó.R. performed the data analysis, revealing the excess power source. E.N. led the theoretical analysis of the nature of the excess. All three authors took part in the discussions, analysis and writing of the paper. All collaborators of this study have fulfilled the criteria for authorship required by Nature Portfolio journals.
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Extended data figures and tables
Extended Data Fig. 1 Time-weighted luminosity light curves for the SNe in our sample.
Error bars are 1σ and include propagated uncertainties in distance, reddening, bolometric correction, and photometry. Solid segments from t = 0 to the first data point are extrapolations of L(t) ⋅ t to t = 0. Black solid lines are Qnuc(t) ⋅ t, namely, the time-weighted energy injection due to the radioactive decay chain 56Ni → 56Co → 56Fe, while dashed lines correspond to the 5th–95th percentile error range due to uncertainties in MNi and tesc.
Extended Data Fig. 2 The effect of change in the estimated explosion time.
Relative change in LT−nuc (a) and LT−nuc/LT100 (b) against change in explosion time. Negative (positive) \(\Delta {t}_{\exp }\) values are quantities computed using \({t}_{{\rm{non-det}}}\) (tdetect) as explosion time. Error bars are 1 σ. Solid lines are straight line fits and dashed lines are \(\pm 1\,\widehat{\sigma }\) limits, where \(\widehat{\sigma }\) is the sample standard deviation.
Extended Data Fig. 3 Correlations between the non-radioactive contribution and various quantities.
LT−nuc (a–f) and LT−nuc/LT100 (g–l) against peak luminosity (a,g), 56Ni mass (b,h), gamma-ray escape time (c,i), peak time (d,j), ejecta velocity at peak time (e,k), and decline rate (f,l). Error bars denote 1 σ errors.
Extended Data Fig. 4 Peak luminosity comparison of our sample to a volume-limited sample.
Cumulative distributions for the absolute r-band magnitudes at peak of the SNe IIb (a), Ib (b), and Ic (c) in our sample (solid lines) and in the volume-limited samples of ref. 7 (dashed lines). Shaded regions represent 68% confidence intervals computed by bootstrap resampling (10,000 samples). Numbers in parentheses are the sample sizes.
Extended Data Fig. 5 The effect of extinction.
LT−nuc (a) and LT−nuc/LT100 (b) against host galaxy reddening. Error bars are 1σ.
Extended Data Fig. 6 The effect of the radioactive energy deposition function.
a. LT−nuc computed with the deposition function of Sharon & Kushnir against the LT−nuc estimates reported in this work. The solid line is a one-to-one correspondence. Error bars are 1σ. b. Cumulative distribution for the ratio of LT−nuc computed with the deposition function of Sharon & Kushnir to LT−nuc reported in this work. Shaded regions represent 68% confidence intervals computed by bootstrap resampling (10,000 samples).
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Rodríguez, Ó., Nakar, E. & Maoz, D. Stripped-envelope supernova light curves argue for central engine activity. Nature 628, 733–735 (2024). https://doi.org/10.1038/s41586-024-07262-x
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DOI: https://doi.org/10.1038/s41586-024-07262-x
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