title: Asymmetries in core-collapse supernovae from maps of radioactive 44Ti in Cassiopeia A.
abstract: 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 (44)Ti, synthesized in an exploding star near the boundary between material falling back onto the collapsing core and that ejected into the surrounding medium, directly probes the explosion asymmetries. Cassiopeia A is a young, nearby, core-collapse remnant from which (44)Ti emission has previously been detected but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed (44)Ti emission to estimated (56)Ni emission, from optical light echoes, and from jet-like features seen in the X-ray and optical ejecta. Here we report spatial maps and spectral properties of the (44)Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the (44)Ti 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.
authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
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authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
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authors.lastname: Harrison
authors.affiliation: Space Sciences Laboratory, University of California, Berkeley, California 94720, USA.
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authors.affiliation: Physics Department, North Carolina State University, Raleigh, North Carolina 27695, USA.
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authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
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authors.affiliation: Space Sciences Laboratory, University of California, Berkeley, California 94720, USA.
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authors.lastname: Ellinger
authors.affiliation: Department of Physics, Durham University, Durham DH1 3LE, UK.
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authors.affiliation: Department of Physics, McGill University, Rutherford Physics Building, Montreal, Quebec H3A 2T8, Canada.
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authors.affiliation: 1] Université de Toulouse, UPS-OMP, IRAP, 9 Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France [2] CNRS, Institut de Recherche en Astrophysique et Planétologie, 9 Avenue colonel Roche, BP 44346, F-31028 Toulouse Cedex 4, France.
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authors.affiliation: DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark.
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authors.affiliation: 1] Space Sciences Laboratory, University of California, Berkeley, California 94720, USA [2] Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
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authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
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authors.affiliation: Department of Physics, McGill University, Rutherford Physics Building, Montreal, Quebec H3A 2T8, Canada.
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authors.affiliation: Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
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authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
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authors.affiliation: Columbia Astrophysics Laboratory, Columbia University, New York, New York 10027, USA.
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authors.affiliation: 1] Agenzia Spaziale Italiana (ASI) Science Data Center, Via del Politecnico snc, I-00133 Roma, Italy [2] INAF - Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio, Italy.
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authors.forename: S
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authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
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authors.affiliation: DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark.
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