Double-peaked Oxygen Lines Are not Rare in Nebular Spectra of   Core-Collapse Supernovae
  Double-peaked oxygen lines in the nebular spectra of two peculiar Type Ib/c Supernovae (SN Ib/c) have been interpreted as off-axis views of a GRB-jet or unipolar blob ejections. Here we present late-time spectra of 8 SN 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 mis-directed GRB jet. 
Maryam Modjaz (1,2), R. P. Kirshner (2), S. Blondin (2), P. Challis   (2), T. Matheson (3) ((1) UC Berkeley, (2) Harvard-Smi...