title: Asphericity in supernova explosions from late-time spectroscopy.
abstract: Core-collapse supernovae (CC-SNe) are the explosions that announce the death of massive stars. Some CC-SNe are linked to long-duration gamma-ray bursts (GRBs) and are highly aspherical. One important question is to what extent asphericity is common to all CC-SNe. Here we present late-time spectra for a number of CC-SNe from stripped-envelope stars and use them to explore any asphericity generated in the inner part of the exploding star, near the site of collapse. A range of oxygen emission-line profiles is observed, including a high incidence of double-peaked profiles, a distinct signature of an aspherical explosion. Our results suggest that all CC-SNe from stripped-envelope stars are aspherical explosions and that SNe accompanied by GRBs exhibit the highest degree of asphericity.
authors.affiliation: Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, Kashiwa-no-ha 5-1-5, Kashiwa City, Chiba 277-8582, Japan. maeda@ea.c.u-tokyo.ac.jp
authors.forename: Keiichi
authors.initials: K
authors.lastname: Maeda
authors.forename: Koji
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authors.lastname: Kawabata
authors.forename: Paolo A
authors.initials: PA
authors.lastname: Mazzali
authors.forename: Masaomi
authors.initials: M
authors.lastname: Tanaka
authors.forename: Stefano
authors.initials: S
authors.lastname: Valenti
authors.forename: Ken'ichi
authors.initials: K
authors.lastname: Nomoto
authors.forename: Takashi
authors.initials: T
authors.lastname: Hattori
authors.forename: Jinsong
authors.initials: J
authors.lastname: Deng
authors.forename: Elena
authors.initials: E
authors.lastname: Pian
authors.forename: Stefan
authors.initials: S
authors.lastname: Taubenberger
authors.forename: Masanori
authors.initials: M
authors.lastname: Iye
authors.forename: Thomas
authors.initials: T
authors.lastname: Matheson
authors.forename: Alexei V
authors.initials: AV
authors.lastname: Filippenko
authors.forename: Kentaro
authors.initials: K
authors.lastname: Aoki
authors.forename: George
authors.initials: G
authors.lastname: Kosugi
authors.forename: Youichi
authors.initials: Y
authors.lastname: Ohyama
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Sasaki
authors.forename: Tadafumi
authors.initials: T
authors.lastname: Takata