VLT spectropolarimetry of the fast expanding type Ia SN 2006X

F. Patat; D. Baade; P. HoflichJ. R. MaundL.WangJ. C. Wheeler

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VLT spectropolarimetry of the fast expanding type Ia SN 2006X

机译：VLT spectropolarimetry of the fast expanding type Ia SN 2006X

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Aims. The main goal of this study is to probe the ejecta geometry and to get otherwise unobtainable information about the explosionmechanism of type Ia Supernovae (SNe).Methods. Using VLT-FORS1 we performed optical spectropolarimetric observations of the type Ia SN 2006X on 7 pre-maximumepochs (day 10 to day 1) and one post-maximum epoch (+39 days).Results. The SN shows strong continuum interstellar polarization reaching about 8 at 4000 A, characterized by a wavelengthdependency that is substantially different from that of the Milky-Way dust mixture. Several SN features, like Si II 6355 A and theCa II IR triplet, present a marked evolution. The Ca II near-IR triplet shows a pronounced polarization (1.4) already on day 10in correspondence with a strong high-velocity feature (HVF). The Si II polarization peaks on day 6 at about 1.1 and decreasesto 0.8 on day 1. By day +39 no polarization signal is detected for the Si II line, while the Ca II IR triplet shows a marked repolarizationat the level of 1.2. As in the case of another strongly polarized SN (2004dt), no polarization was detected across theO I 7774 A absorption.Conclusions. The fast-expanding SN 2006X lies on the upper edge of the relation between peak polarization and decline rate, andit confirms previous speculations about a correlation between degree of polarization, expansion velocity, and HVF strength. Thepolarization of Ca II detected in our last epoch, the most advanced ever obtained for a type Ia SN, coincides in velocity with theouter boundary of the Ca synthesized during the explosion (15 000–17 000 km s1) in delayed-detonation models. This suggests alarge scale chemical inhomogeneity as produced by off-center detonations, a rather small amount of mixing, or a combination ofboth effects. In contrast, the absence of polarization at the inner edge of the Ca-rich layer (8000–10 000 km s1) implies a substantialamount of mixing in these deeper regions.

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《Astronomy and astrophysics》 |2009年第1期|229-246|共18页
作者
F. Patat; D. Baade; P. HoflichJ. R. MaundL.WangJ. C. Wheeler;
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作者单位

European Organization for Astronomical Research in the Southern Hemisphere (ESO), K. Schwarzschild-str. 2,85748 Garching b. München, Germany;

Department of Physics, Florida State University, Tallahassee, Florida 32306-4350, USA;

Department of Astronomy and McDonald Observatory, The University of Texas at Austin, Austin, TX 78712, USADark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark;

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正文语种英语
中图分类天文学;
关键词
stars; upernovae; general – stars; ndividual; 2006X – ISM; general – dust; extinction;

VLT spectropolarimetry of the fast expanding type Ia SN 2006X

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