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Spectropolarimetry of SN2014J in M82: another low R(V) event

ATel #5830; F. Patat (ESO), S. Taubenberger (MPA), D. Baade (ESO), P. Hoeflich (FSU), J. Maund (QUB), E. Reilly (QUB), J. Spyromilio (ESO), L. Wang (TAMU), J. C. Wheeler (Texas University - Austin) and P. Zelaya (PUC)
on 29 Jan 2014; 16:19 UT
Credential Certification: Ferdinando Patat (fpatat@eso.org)

Subjects: Supernovae

Referred to by ATel #: 5840, 5851, 5965

We obtained linear spectro-polarimetry of SN2014J in M82 using CAFOS mounted at the 2.2-m telescope at Calar Alto (Spain) on January 28.16 UT. The spectrum covers the wavelength range 3800-8800A, with a resolution of 14A (FWHM). A preliminary analysis of the data shows a marked continuum polarization, reaching about 6.5% in the blue and decreasing to about 2% in the red. We identify the bulk of this polarization as arising in the inter-stellar (IS) medium. Similarly to what was observed for two other significantly reddened Type Ia SN2006X and SN2008fp, there are no signs of a maximum polarization peak in the wavelength range covered by our data. This indicates that the dust grains along the line-of-sight to SN2014J are significantly smaller than what is typical in the Galaxy. In turn, it implies a small value for the total-to-selective extinction ratio. The absence of a maximum polarization peak above 3800A suggests that R(V)<2. This confirms rough R(V) estimates based on the E(B-V) derived from high-resolution spectroscopy (e.g. ATEL#5797), the distance modulus to M82 and the brightness reached by the object. A very preliminary subtraction of the IS polarization reveals an intrinsic polarization of 0.5 +/- 0.1% coinciding with the SiII absorption. This value is typical of Type Ia Supernovae at maximum light. Polarization at a similar level (although less statistically significant) is present in the CaII NIR triplet.