Grefenstette, B.W. and Harrison, F.A. and Boggs, S.E. and Reynolds, S.P. and Fryer, C.L. and Madsen, K.K. and Wik, D.R. and Zoglauer, A. and Ellinger, C.I. and Alexander, D.M. and An, H. and Barret, D. and Christensen, F.E. and Craig, W.W. and Forster, K. and Giommi, P. and Hailey, C.J. and Hornstrup, A. and Kaspi, V.M. and Kitaguchi, T. and Koglin, J.E. and Mao, P.H. and Miyasaka, H. and Mori, K. and Perri, M. and Pivovaroff, M.J. and Puccetti, S. and Rana, V. and Stern, D. and Westergaard, N.J. and Zhang, W.W. (2014) 'Asymmetries in core-collapse supernovae from maps of radioactive 44Ti in CassiopeiaA.', Nature., 506 (7488). pp. 339-342.
Asymmetry is required by most numerical simulations of stellar core-collapse explosions, but the form it takes differs significantly among models. The spatial distribution of radioactive 44Ti, synthesized in an exploding star near the boundary between material falling back onto the collapsing core and that ejected into the surrounding medium1, directly probes the explosion asymmetries. Cassiopeia A is a young2, nearby3, core-collapse4 remnant from which 44Ti emission has previously been detected5, 6, 7, 8 but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed 44Ti emission to estimated 56Ni emission9, from optical light echoes10, and from jet-like features seen in the X-ray11 and optical12 ejecta. Here we report spatial maps and spectral properties of the 44Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the 44Ti and iron X-ray emission, the latter being visible only in shock-heated material. The observed spatial distribution rules out symmetric explosions even with a high level of convective mixing, as well as highly asymmetric bipolar explosions resulting from a fast-rotating progenitor. Instead, these observations provide strong evidence for the development of low-mode convective instabilities in core-collapse supernovae.
|Keywords:||High-energy astrophysics, Particle astrophysics.|
|Full text:||(AM) Accepted Manuscript|
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|Publisher Web site:||http://dx.doi.org/10.1038/nature12997|
|Date accepted:||No date available|
|Date deposited:||21 May 2015|
|Date of first online publication:||February 2014|
|Date first made open access:||No date available|
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