Gorosabel 2008 SN2008D/XRF080109 polarization

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Title:		Simultaneous polarization monitoring of SN2007uy and the axisymmetric SN2008D/XRF080109: isolating geometry from dust
Authors:		Gorosabel, J.; de Ugarte Postigo, A.; Castro-Tirado, A. J.; Agudo, I.; Jelinek, M.; Leon, S.; Augusteijn, T.; Fynbo, J. P. U.; Hjorth, J.; Michalowski, M. J.; Xu, D.; Ferrero, P.; Kann, D. A.; Klose, S.; Rossi, A.; Madrid, J. P.; LLorente, A.; Bremer, M.; Winters, J. -M.
Publication:		eprint arXiv:0810.4333
Publication Date:		10/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		4 pages, 1 figure, submitted to ApJL. Comments welcome
Bibliographic Code:		2008arXiv0810.4333G

Abstract

We report the results of an optical linear polarization monitoring carried out simultaneously for SN2007uy and SN2008D. The observations span 74.9 days, starting 3.6 days after the X-ray outburst of SN2008D and are distributed in 11 visits. For both SNe the polarization is dominated by the host galaxy interstellar polarization (HGIP), especially for SN2007uy. This fact is supported by 1.2 millimeter (mm) observations of NGC2770, carried out at and around the SN2008D position. The 1.2 mm data are consistent with no intrinsic emission from SN2008D and can be entirely explained by the NGC2770 dust emission. Comparing spectroscopic extinction values reported in the literature with the extinction derived from the 1.2 mm data, we conclude that the NGC2770 extinction distribution is heterogeneous. We report also a 3.3 mm flux detection at the SN2008D position, possibly due to the intrinsic SN emission, and not due to the dust. Despite the dominant HGIP, a statistical analysis of the distribution of the SN2008D Stokes parameters strongly suggests an intrinsic variable polarization component. Moreover we show that the temporal evolution of the intrinsic SN2008D polarization agrees with an aspherical axisymmetric expansion with variable eccentricity, consistent with the Collapsar model. In contrast, the SN2007uy polarization can be described by the HGIP plus a constant eccentricity expansion. We conclude that the geometric evolution of the two SNe is intrinsically different.

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