Two birds with one stone: Simultaneous optical polarization monitoring of SN2007uy and XRF080109/SN2008D. Javier Gorosabel Consejo Superior de Investigaciones Científicas Instituto de Astrofísica de Andalucía, Granada, Spain

A. de Ugarte Postigo (ESO, Chile), A.J. Castro-Tirado (IAA-CSIC, Spain), M. Jelínek (IAA-CSIC, Spain), A. LLorente (ESAC, Spain), J. Fynbo (DARK, Denmark), J. Hjorth (DARK, Denmark), D. Malesani (DARK, Denmark), T. Augusteijn (NOT, Spain), S. Klose (TLS, Germany), A. Rossi (TLS, Germany), P. Ferrero (TLS, Germany), A. Kann (TLS, Germany), J. P. Madrid (Univ. of Mc. Master, Canada), S. Guziy (IAA-CSIC, Spain). Collaborators:

What is a Gamma-Ray Bursts (GRB)? Duration (seconds) Number of GRBs  Two main groups of GRBs (Kouvelioutou et al. 1993) : short and long GRBs.

Collapsar/Hypernova model 1 Collapse of a massive star via an accretion disk around a rotating black hole Collimated bipolar outflows drill the star Internal shocks in the jet produce the GRB Interaction with the interstellar medium originates the afterglow The star explodes as a Ib /c SN. 5 Hypernova  Is 5 spherical?  As for usual SN we assume that the observed optical light from 5 is dominated by Thomson scattering.  We aim to infer geometric information of 5 by means of optical linear polarization measurements.  Is the shape of 5 still influenced by the geometry of the previous non radial collapse?

The long GRB diversity Sollerman et al. (2006)  XRFs are detected at low redshift, specially the ones dominated by SNe.  Low detection rate of XRFs dominated by SNe. At most 5 well studied XRFs so far.

Polarization by Thomson scattering:  The stellar photospheres contain free electrons.  If the input radiation field is anisotropic linear polarization.  If the input radiation field is isotropic NO linear polarization.

Thomson scattering in SNe photospheres: P=0 Kasen et al P= Kasen et al We intend to obtain geometric information of the source well below our resolution.

Q U  The combined Stokes parameters should be constrained to a straight line offset from the origin (Wang et al. 2001). Axisymmetric SN embedded in a host galaxy: Measurements ISP

SN2008D/XRF080109: X-ray Flash, He-rich Ib/c-type SN. SN2007uy: no X-ray Flash. Ib-type SN. Hunting two birds with the same shot.  SN2008D/XRF and SN2007uy in NGC2770: SN2007uy SN2008D/XRF Unprecedented opportunity to compare the geometries of a standard SN and a hypernova

2.2m Calar Alto 2.5m NOT 8.2m VLT Observations and data analysis:  We carried out 11 polarimetric visits, from 5 to 78 days after the XRF of the visits covered both SNe at the same time.

SN2007uy SN2008D Gorosabel et al Main results on XRF080109/SN2008D  SN2007uy shows a probability of 0.56 that U and Q are constant 56%  SN2008D shows a probability of 4.3x10 -4 that both U and Q are constant 0.043%

SN2007uy SN2008D Gorosabel et al Main results on XRF080109/SN2008D  If we assume that the SN2007uy geometry is constant SN2008D shows variable axisymmetric geometry. SN2007uy SN2008D Gorosabel et al SN2007uy SN2008D Χ 2 /dof ~ 0.3

Summary  XRF080109/SN2008D vs. SN2007uy: First optical polarimetric monitoring done simultaneously for 2 SNe. The projected geometry on the sky plane of XRF080109/SN2008D and SN2007uy is statistically different. SN2007uy polarization is consistent with constant eccentricity. XRF080109/SN2008D polarization is NOT consistent with constant eccentricy. XRF080109/SN2008D geometry is consistent with axial symmetry. One of the most convincing evidences so far that SNe and hypernovae show different geometries. Results in Gorosabel et al. (2009), ApJ in press, arXiv )

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