2020ApJ...888...93G

Observations toward type Ia supernovae (SNe Ia) frequently report an unusually low total-to-selective extinction ratio (R_V < 2) and a small peak wavelength of polarization (λ_max < 0.4 µm). Hoang et al. proposed that the dominance of small grains near SNe Ia due to RAdiative Torque Disruption (RATD) can explain the puzzle. To test this scenario, we model the dust extinction and polarization of SNe Ia, accounting for grain disruption and alignment by radiative torques and different grain tensile strengths from S_{max}=10⁷–10¹⁰ergcm^–3. We find that R_V decreases from ∼3.1 to ∼1.5 after disruption time t_disr < 40 days for clouds at a distance d < 4 pc from SNe Ia. We then calculate the observed lightcurves of SNe Ia and find that their colors change with time, due to varying dust extinction. The peak wavelength λ_max also decreases from ∼0.55 to ∼0.15 µm over an alignment time of t_align < 10 days, due to the enhanced alignment of small grains. By fitting the theoretical polarization with the Serkowski law characterized by the K and λ_max parameters, we find that K increases when large grains are disrupted by RATD, which is consistent with the unusual K versus λ_max relationship of SNe Ia. Nevertheless, an accurate measurement of K and λ_max is challenging, due to atmospheric effects and potential contamination of polarization by Rayleigh scattering by circumstellar matter. Our results demonstrate the importance of RATD for time-dependent extinction, polarization, and colors of SNe Ia.