Spectropolarimetry of the Thermonuclear Supernova SN 2021rhu: High Calcium Polarization 79 Days after Peak Luminosity

Abstract We report spectropolarimetric observations of the Type Ia supernova (SN) SN 2021rhu at four epochs: ?7, +0, +36, and +79 days relative to its B -band maximum luminosity. A wavelength-dependent continuum polarization peaking 3890 ± 93 Å reaching a level p max = 1.78 % ± 0.02 % was found. The peak curve is bluer than typical in Milky Way, indicating larger proportion small dust grains along sight line SN. After removing interstellar polarization, we found pronounced increase Ca ii near-infrared triplet, from ?0.3% day ?7 ?2.5% +79. No temporal evolution high-resolution flux spectra across Na i D H K features seen +39 +74, that late-time intrinsic as opposed being caused by scattering photons circumstellar or matter. suggest an explanation for rise triplet may be alignment calcium atoms weak magnetic field through optical excitation/pumping anisotropic radiation