A faint type of supernova from a white dwarf with a helium-rich companion

Creators: Perets, Hagai B.; Gal-Yam, A.; Mazzali, P. A.; Arnett, D.; Kagan, D.; Filippenko, A. V.; Li, W.; Arcavi, I.; Cenko, S. B.; Fox, D. B.; Leonard, D. C.; Moon, D.-S.; Sand, D. J.; Soderberg, A. M.; Anderson, J. P.; James, P. A.; Foley, R. J.; Ganeshalingam, M.; Ofek, E. O.; Bildsten, L.; Nelemans, G.; Shen, K. J.; Weinberg, N. N.; Metzger, B. D.; Piro, A. L.; Quataert, E.; Kiewe, M.; Poznanski, D.

Abstract

Supernovae are thought to arise from two different physical processes. The cores of massive, short-lived stars undergo gravitational core collapse and typically eject a few solar masses during their explosion. These are thought to appear as type Ib/c and type II supernovae, and are associated with young stellar populations. In contrast, the thermonuclear detonation of a carbon-oxygen white dwarf, whose mass approaches the Chandrasekhar limit, is thought to produce type Ia supernovae. Such supernovae are observed in both young and old stellar environments. Here we report a faint type Ib supernova, SN 2005E, in the halo of the nearby isolated galaxy, NGC 1032. The 'old' environment near the supernova location, and the very low derived ejected mass (~0.3 solar masses), argue strongly against a core-collapse origin. Spectroscopic observations and analysis reveal high ejecta velocities, dominated by helium-burning products, probably excluding this as a subluminous, or a regular type Ia supernova. We conclude that it arises from a low-mass, old progenitor, likely to have been a helium-accreting white dwarf in a binary. The ejecta contain more calcium than observed in other types of supernovae and probably large amounts of radioactive ^(44)Ti.

Additional Information

© 2010 Macmillan Publishers Limited. Received 17 May 2009; Accepted 23 March 2010. We thank P. Podsiadlowski, E. Nakar and D. Maoz for comments. We acknowledge observations with the Liverpool Telescope, and various telescopes at the Lick, Palomar and Keck Observatories. We are grateful to the staffs of these observatories, as well as to the institutions, agencies and companies funding these facilities. This research also made use of the NASA/IPAC Extragalactic Database (NED). H.B.P. acknowledges the ISF/FIRST and Ilan Ramon-Fulbright Fellowships, and is a Harvard-Smithsonian Center for Astrophysics Fellow. The collaborative work of A.G.-Y. and P.A.M. is supported by a Weizmann-Minerva grant. A.G.-Y. acknowledges further support by the Israeli Science Foundation, an EU Seventh Framework Programme Marie Curie IRG Fellowship, the Benoziyo Center for Astrophysics, and the Peter and Patricia Gruber Awards. A.V.F. is grateful for the support of the US National Science Foundation, the US Department of Energy, Gary and Cynthia Bengier, the Richard and Rhoda Goldman Fund, the Sylvia & Jim Katzman Foundation, and the TABASGO Foundation. R.J.F. is a Clay Fellow. Author Contributions: H.B.P. led the project, performed the calculations related to hyper-velocity stars, examined other putative SN 2005E-like events, collected and analysed archival data concerning supernova properties and their hosts, and wrote the manuscript. A.G.-Y. is the Principal Investigator of the CCCP programme and initiated the project, collected and analysed photometric and spectroscopic data, coordinated further observational and theoretical work, and managed the project. P.A.M. conducted the nebular spectral analysis and its interpretation, and determined the elemental abundances in the ejecta. D.A. determined that the measured composition requires He burning and performed nucleosynthesis calculations to confirm this. D.K. investigated local star-formation tracers at the location of SN 2005E. A.V.F. and W.L. contributed spectroscopic and photometric observations and reductions of SN 2005E and of similar Ca-rich objects, a class they originally identified, and provided most of the data on supernova host galaxies. A.V.F. also edited the paper. I.A. analysed the CCCP photometry of SN 2005E and cross-calibrated it with other data. S.B.C., D.B.F., D.C.L., D.-S.M., D.J.S. and A.M.S. are members of the CCCP and contributed to initial observations of SN 2005E. J.P.A. and P.A.J. obtained and analysed narrow-band images of NGC 1032 and the location of SN 2005E. R.J.F. and M.G. contributed to spectroscopic observations and reductions. E.O.O. obtained deep photometric observations of the location of SN 2005E. L.B., G.N., K.J.S. and N.N.W. investigated the relation of SN 2005E to .Ia models and contributed to the text. B.D.M., A.L.P. and E.Q. investigated the relation of SN 2005E to accretion-induced collapse models and contributed to the text. M.K. performed custom reductions of CCCP spectra. D.P. carried out synthetic photometry analysis.

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Supplemental Material - nature09056-s1.pdf

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