%AHoeflich, Peter%AYang, Yi%ABaade, Dietrich%ACikota, Aleksandar%AMaund, Justyn%AMishra, Divya%APatat, Ferdinando%APatra, Kishore%AWang, Lifan%AWheeler, J.%AFilippenko, Alexei%AGal-Yam, Avishay%ASchulze, Steven%BJournal Name: Monthly Notices of the Royal Astronomical Society; Journal Volume: 520; Journal Issue: 1; Related Information: CHORUS Timestamp: 2024-01-16 01:18:43 %D2023%IOxford University Press %JJournal Name: Monthly Notices of the Royal Astronomical Society; Journal Volume: 520; Journal Issue: 1; Related Information: CHORUS Timestamp: 2024-01-16 01:18:43 %K %MOSTI ID: 10394865 %PMedium: X; Size: p. 560-582 %TThe core normal Type Ia supernova 2019np – an overall spherical explosion with an aspherical surface layer and an aspherical 56Ni core %XABSTRACT

Optical spectropolarimetry of the normal thermonuclear supernova (SN) 2019np from −14.5 to +14.5 d relative to B-band maximum detected an intrinsic continuum polarization (pcont) of 0.21 ± 0.09 per cent at the first epoch. Between days −11.5 and  +0.5, pcont remained ∼0 and by day +14.5 was again significant at 0.19 ± 0.10 per cent. Not considering the first epoch, the dominant axis of ${\rm Si\, {\small II}}$ λ6355 was roughly constant staying close the continuum until both rotated in opposite directions on day  +14.5. Detailed radiation-hydrodynamical simulations produce a very steep density slope in the outermost ejecta so that the low first-epoch pcont ≈ 0.2 per cent nevertheless suggests a separate structure with an axis ratio ∼2 in the outer carbon-rich (3.5–4) × 10−3 M⊙. Large-amplitude fluctuations in the polarization profiles and a flocculent appearance of the polar diagram for the ${\rm Ca\, {\small II}}$ near-infrared triplet (NIR3) may be related by a common origin. The temporal evolution of the polarization spectra agrees with an off-centre delayed detonation. The late-time increase in polarization and the possible change in position angle are also consistent with an aspherical 56Ni core. The pcont and the absorptions due to ${\rm Si\, {\small II}}$ λ6355 and ${\rm Ca\, {\small II}}$ NIR3 form in the same region of the extended photosphere, with an interplay between line occultation and thermalization producing p. Small-scale polarization features may be due to small-scale structures, but many could be related to atomic patterns of the quasi-continuum; they hardly have an equivalent in the total-flux spectra. We compare SN 2019np to other SNe and develop future objectives and strategies for SN Ia spectropolarimetry.

%0Journal Article