Double-Peaked Oxygen Lines Are Not Rare in Nebular Spectra of Core-Collapse Supernovae

Abstract

Double-peaked oxygen lines in the nebular spectra of two peculiar Type Ib/c supernovae (SNe Ib/c) have been interpreted as off-axis views of a GRB jet or unipolar blob ejections. Here we present late-time spectra of eight SNe IIb, Ib, and Ic and show that this phenomenon is common and should not be so firmly linked to extraordinary explosion physics. The line profiles are most likely caused by ejecta expanding with a torus- or disk-like geometry. Double-peaked oxygen profiles are not necessarily the indicator of a misdirected GRB jet.