2021/10/21 by Douglas C. Leonard, Luc Dessart, D. John Hillier +11
Physics and Astronomy · #Astronomy #Astrophysics #Ejecta #Flux (metallurgy) #Galaxy #Gamma-ray bursts and supernovae #Neutrino Physics Research #Opacity #Optics #Physics #Radiative transfer #Redshift #Scattering #Stellar, planetary, and galactic studies #Supernova #astro-ph.HE #astro-ph.SR
paper · pdf · doi:10.3847/2041-8213/ac31bf
published in The Astrophysical Journal Letters 921(2), L35 (IOP Publishing) · Accepted for publication in The Astrophysical Journal Letters
arxiv created 2021/10/21 · openalex publication_date 2021/11/01 · arxiv updated 2021/11/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Abstract We present deep, nebular-phase spectropolarimetry of the Type II-P/L SN 2013ej, obtained 167 days after explosion with the European Southern Observatory’s Very Large Telescope. The polarized flux spectrum appears as a nearly perfect (92% correlation), redshifted (by ∼4000 km s −1 ) replica of the total flux spectrum. Such a striking correspondence has never been observed before in nebular-phase supernova spectropolarimetry, although data capable of revealing it have heretofore been only rarely obtained. Through comparison with 2D polarized radiative transfer simulations of stellar explosions, we demonstrate that localized ionization produced by the decay of a high-velocity, spatially confined clump of radioactive 56 Ni—synthesized by and launched as part of the explosion with final radial velocity exceeding 4500 km s −1 —can reproduce the observations through enhanced electron scattering. Additional data taken earlier in the nebular phase (day 134) yield a similarly strong correlation (84%) and redshift, whereas photospheric-phase epochs that sample days 8 through 97 do not. This suggests that the primary polarization signatures of the high-velocity scattering source only come to dominate once the thick, initially opaque hydrogen envelope has turned sufficiently transparent. This detection in an otherwise fairly typical core-collapse supernova adds to the growing body of evidence supporting strong asymmetries across nature’s most common types of stellar explosions, and establishes the power of polarized flux—and the specific information encoded by it in line photons at nebular epochs—as a vital tool in such investigations going forward.