Time-varying Extinction, Polarization, and Colors of Type Ia Supernovae due to Rotational Disruption of Dust Grains

Abstract

Abstract 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 . 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.