Spectropolarimetry of the Type Ib Supernova iPTF 13bvn: revealing the complex explosion geometry of a stripped-envelope core-collapse supernova. Issue 1 (20th January 2016)

• Record Type: Journal Article
• Authors: Reilly, Emma; Maund, Justyn R.; Baade, Dietrich; Wheeler, J. Craig; Silverman, Jeffrey M.; Clocchiatti, Alejandro; Patat, Ferdinando; Höflich, Peter; Spyromilio, Jason; Wang, Lifan; Zelaya, Paula
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 457:Issue 1(2016)
• Page Start: 288
• Page End: 303
• Publication Date: 2016-01-20
• Subjects: techniques: polarimetric -- supernovae: general -- supernovae: individual: iPTF 13bvn; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stv3005
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: We present six epochs of spectropolarimetric observations and one epoch of spectroscopy of the Type Ib SN iPTF 13bvn. The epochs of these observations correspond to −10 to +61 d with respect to the r -band light-curve maximum. The continuum is intrinsically polarized to the 0.2–0.4 per cent level throughout the observations, implying asphericities of ∼10 per cent in the shape of the photosphere. We observe significant line polarization associated with the spectral features of Ca ii ir3, He i /Na i d, He i λλ6678, 7065, Fe ii λ4924 and O i λ7774. We propose that an absorption feature at ∼6200 Å, usually identified as Si ii λ6355, is most likely to be high-velocity H α at −16 400 km s −1 . Two distinctly polarized components, separated in velocity, are detected for both He i /Na i d and Ca ii ir3 , indicating the presence of two discrete line-forming regions in the ejecta in both radial velocity space and in the plane of the sky. We use the polarization of He i λ5876 as a tracer of sources of non-thermal excitation in the ejecta; finding that the bulk of the radioactive nickel was constrained to lie interior to ∼50–65 per cent of the ejecta radius. The observed polarization is also discussed in the context of the possible progenitor system of iPTF 13bvn, with our observations favouring the explosion of a star with an extended, distorted envelope rather than a compact Wolf–Rayet star.