A strong ultraviolet pulse from a newborn type Ia supernova


  • An Erratum to this article was published on 24 June 2015


Type Ia supernovae1 are destructive explosions of carbon-oxygen white dwarfs2,3. Although they are used empirically to measure cosmological distances4,5,6, the nature of their progenitors remains mysterious3. One of the leading progenitor models, called the single degenerate channel, hypothesizes that a white dwarf accretes matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion3,7,8. Here we report observations with the Swift Space Telescope of strong but declining ultraviolet emission from a type Ia supernova within four days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the supernova and a companion star9, and therefore provides evidence that some type Ia supernovae arise from the single degenerate channel.

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Figure 1: Swift/UVOT lightcurves of iPTF14atg.
Figure 2: The spectral energy distribution of iPTF14atg.
Figure 3: The multi-colour lightcurve of iPTF14atg.
Figure 4: Spectral evolution of iPTF14atg.


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We thank A. L. Piro, M. Kromer and J. Cohen for discussions. We also thank A. Waszczak, A. Rubin, O. Yaron, A. De Cia, D. A. Perley, G. E. Duggan, O. Smirnova, S. Papadogiannakis, A. Nyholm, Y. F. Martinez and the staff at the Nordic Optical Telescope and Gemini for observation and data reduction. Some of the data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA. The observatory was made possible by the generous financial support of the W. M. Keck Foundation. Some data were obtained with the Nordic Optical Telescope, which is operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain. This work also makes use of observations from the Las Cumbres Observatory Global Telescope (LCOGT) network. Research at California Institute of Technology is supported by the National Science Foundation. D.A.H. acknowledges support from the National Science Foundation. A.G.-Y. acknowledges support from the EU/FP7 via an ERC grant, the “Quantum Universe” I-Core programme, the ISF, Minerva and Weizmann-UK grants, and the Kimmel Award. M.M.K. acknowledges generous support from the Carnegie-Princeton fellowship. Supernova research at the Oskar Klein Centre is supported by the Swedish Research Council and by the Knut and Alice Wallenberg Foundation. The National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US Department of Energy under contract number DE-AC02-05CH11231, provided staff, computational resources, and data storage for this project. The participation of the Los Alamos National Laboratory (LANL) in iPTF is supported by the US Department of Energy as part of the Laboratory Directed Research and Development programme. A portion of this work was carried out at the Jet Propulsion Laboratory under a Research and Technology Development Grant, under contract with the National Aeronautics and Space Administration.

Author information

Y.C. initiated the study, conducted analysis and wrote the manuscript. S.R.K. is the iPTF Principal Investigator, and contributed to Swift/UVOT data analysis and manuscript preparation. S.V. and D.A.H. contributed to LCOGT observation, data analysis and manuscript preparation. A.G.-Y. contributed to manuscript preparation. M.M.K. contributed to Swift, Apache Point Observatory and Gemini-North spectroscopic observations and manuscript preparation. J.J., A.G., J.S., F.T. and R.A. triggered early Nordic Optical Telescope observation and contributed to manuscript preparation. A.H. triggered the Jansky Very Large Array observation and analysed the data. I.S. found the supernova. S.B.C. reduced the P48 data and contributed to manuscript preparation. P.E.N. contributed to manuscript preparation. J.S. and I.A. contributed to building transient vetting and data archiving software. B.D.B., D.I.M., U.D.R. and P.R.W. contributed to the machine learning codes to search for young transients. N.G. is the Swift Principal Investigator.

Correspondence to Yi Cao.

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Extended data figures and tables

Extended Data Figure 1 Comparative analysis of iPTF14atg lightcurve.

The lightcurves of iPTF14atg are compared to the Nugent template light curves of SN 1991bg-like events, (the Nugent supernova template is available at https://c3.lbl.gov/nugent/nugent_templates.html), and observed lightcurves of a typical SN 2002cx-like event SN 2005hk and SN 2002es. The error bars denote 1σ uncertainties of magnitudes. The red triangles are upper limits at a 99.9999% CL for non-detections of iPTF14atg.

Extended Data Figure 2 Comparative analysis of iPTF14atg colour evolution.

The colour curves of iPTF14atg are compared to SN 1991bg, SN 2005hk, SN 2002es and a normal event SN 2011fe. The error bars denote 1σ uncertainties.

Extended Data Figure 3 The spectral evolution of iPTF14atg.

Ticks at the top of the figure label major absorption features.

Extended Data Figure 4 Comparative analysis of iPTF14atg spectra.

The spectra of iPTF14atg at different phases are compared with those of SN 1991bg, SN 2005bl (SN 1991bg-like), SN 2005hk, SN 2002es and PTF10ujn (SN 2002es-like) at similar phases.

Extended Data Table 1 Spectroscopic observation log
Extended Data Table 2 Swift Observation of iPTF14atg

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Cao, Y., Kulkarni, S., Howell, D. et al. A strong ultraviolet pulse from a newborn type Ia supernova. Nature 521, 328–331 (2015). https://doi.org/10.1038/nature14440

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