We present the first spectropolarimetric observations of a candidate of super-Chandrasekhar mass Type Ia supernova ( SN ) : SN 2009dc .
The observations were performed at 5.6 and 89.5 days after the B -band maximum .
The data taken at the later epoch are used to determine the interstellar polarization .
Continuum polarization is found to be small ( < 0.3 \% ) , indicating that the explosion is nearly spherically symmetric .
This fact suggests that a very aspherical explosion is not a likely scenario for SN 2009dc .
Polarization at the Si ii and Ca ii lines clearly shows a loop in the Q - U plane , indicating a non-axisymmetric , clumpy distribution of intermediate-mass elements .
The degree of line polarization at the Si and Ca line is moderate ( 0.5 \% \pm 0.1 \% and 0.7 \% \pm 0.1 \% , respectively ) , but it is higher than expected from the trend of other Type Ia SNe .
This may suggest that there are thick enough , clumpy Si-rich layers above the thick ^ { 56 } Ni-rich layers ( \mathrel { \hbox to 0.0 pt { \lower 4.0 pt \hbox { $ \sim$ } } \raise 1.0 pt \hbox { $ > $ } } 1.2 M _ % { \odot } ) .
The observed spectropolarimetric properties , combined with the photometric and spectroscopic properties , suggest that the progenitor of SN 2009dc has a super-Chandrasekhar mass , and that the explosion geometry is globally spherically symmetric , with clumpy distribution of intermediate-mass elements .