Examinando por Autor "Dessart, Luc"

Mostrando 1 - 2 de 2
  • No hay miniatura disponible
    Ítem
    A high-velocity scatterer revealed in the thinning ejecta of a type II supernova
    (American Astronomical Society, 2021-11-10) Leonard, Douglas C.; Dessart, Luc; Hillier, D. John; Pignata, Giuliano; Williams, G. Grant; Hoffman, Jennifer L.; Milne, Peter; Smith, Nathan; Smith, Paul S.; Khandrika, Harish G.
    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 56Ni—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. © 2021. The Author(s). Published by the American Astronomical Society.
  • Miniatura
    Ítem
    A Spectropolarimetric Comparison of the Type II-Plateau Supernovae SN 2008bk and SN 2004dj
    (2011) Leonard, Douglas; Dessart, Luc; Hillier, Jhon; Pignata, Guiliano
    The Type II-Plateau supernova (SN II-P) SN 2004dj was the first SN II-P for which spectropolarimetry data were obtained with fine temporal sampling before, during, and after its fall off of the photometric plateau – the point that marks the transition from the photospheric to the nebular phase in SNe II-P. Unpolarized during the plateau, SN 2004dj showed a dramatic spike in polarization during the descent off of the plateau, and then exhibited a smooth polarization decline over the next two hundred days. This behavior was interpreted by Leonard et al. (2006) as evidence for a strongly non-spherical explosion mechanism that had imprinted asphericity only in the innermost ejecta. In this brief report, we compare nine similarly well-sampled epochs of spectropolarimetry of the Type II-P SN 2008bk to those of SN 2004dj. In contrast to SN 2004dj, SN 2008bk became polarized well before the end of the plateau and also retained a nearly constant level of polarization through the early nebular phase. Curiously, although the onset and persistence of polarization differ between the two objects, the detailed spectropolarimetric characteristics at the epochs of recorded maximum polarization for the two objects are extremely similar, feature by feature. We briefly interpret the data in light of non-Local-Thermodynamic Equilibrium, time-dependent radiative-transfer simulations specifically crafted for SN II-P ejecta.