Double-peaked Oxygen Lines Are not Rare in Nebular Spectra of Core-Collapse Supernovae

TL;DR

Double-peaked oxygen emission lines are common in nebular spectra of various core-collapse supernovae and are likely caused by torus- or disk-like ejecta geometries, not necessarily indicating off-axis gamma-ray bursts.

Contribution

This study demonstrates that double-peaked oxygen lines are prevalent in nebular spectra of multiple supernova types, challenging previous links to unusual explosion physics.

Findings

Double-peaked oxygen lines are common in nebular spectra.

Ejecta geometry is likely torus- or disk-shaped.

Such profiles are not exclusive indicators of off-axis GRB jets.

Abstract

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.