Properties and Alignment of Interstellar Dust Grains toward Type Ia Supernovae with Anomalous Polarization Curves

Abstract

Recent photometric and polarimetric observations of type Ia supernovae (SNe Ia) show unusually low total-to-selective extinction ratio (R V < 2) and wavelength of maximum polarization (λ max < 0.4 µm) for several SNe Ia, which indicates peculiar properties of interstellar (IS) dust in the SN hosted galaxies and/or the presence of circumstellar (CS) dust. In this paper, we use inversion technique to infer bestfit grain size distribution and alignment function of interstellar grains along the lines of sight toward four SNe Ia with anomalous extinction and polarization data (SNe 1986G, 2006X, 2008fp, and 2014J). We find that to reproduce low values of R V , a significant enhancement in the mass of small grains of radius a < 0.1 µm is required. For SN 2014J, a simultaneous fit to its observed extinction and polarization is unsuccessful if the entire data are attributed to IS dust (model 1), but a good fit is obtained when accounting for the contribution of CS dust (model 2). For SN 2008fp, our best-fit results for model 1 show that, to reproduce an extreme value of λ max ∼ 0.15 µm, small silicate grains must be aligned as efficiently as big grains. For this case, we suggest that strong radiation from the SN can induce efficient alignment of small grains in a nearby intervening molecular cloud via radiative torque mechanism. The resulting time dependence polarization from this RAT alignment model can be tested by observing at ultraviolet wavelengths.

On the Time Variation of Dust Extinction and Gas Absorption for Type Ia Supernovae Observed through a Nonuniform Interstellar Medium

“…As is well known, for molecules and small dust particles ( 10 nm for optical wavelengths; Kruegel 2003), the scattering cross section depends on the wavelength as λ −4 . Contribution from Rayleigh scattering has been invoked as a possible explanation for the sharp blue rise in spectropolarimetry for sight lines toward certain stars (Andersson et al 2013) in the MW (scattering by a reflection nebula) and toward SN 2014J (Patat et al 2015;Hoang 2017), respectively. In the limit of Rayleigh scattering, R V would be given by R , Bessell 1990).…”

“…Indeed, for most SNe Ia, observational evidence points in the direction of interstellar dust being at least the dominant cause for extinction, including those that are highly reddened (e.g., Patat et al 2007;Chotard et al 2011;Phillips et al 2013;Patat et al 2015;Maeda et al 2016;Zelaya et al 2017;Huang et al 2017;Bulla et al 2017). The low values of R V and λ max for some SNe Ia may then be the result of the dust grain size distribution in some of the host galaxies being different from the MW and/or possibly having been altered by SN radiation (e.g., Hoang 2017). In short, the nature and properties of extragalactic dust toward SNe Ia have been a long standing puzzle, and a deeper understanding is important for cosmology, SN progenitor (for a recent review, see, e.g., Maoz et al 2014), and ISM studies.…”

“…To account for the "peculiar" dust properties for SNe Ia, it has been suggested that scattered light by dust in a circumstellar medium (CSM) associated with an SN Ia may provide an explanation for both the low values of R V (Wang 2005;Patat et al 2006;Goobar 2008) and λ max (Patat et al 2015;Hoang 2017). Observationally, CSM indeed seems to be present for at least some SNe Ia, as evidenced by the detection of SN-CSM interactions (e.g, Hamuy et al 2003;Aldering et al 2006;Dilday et al 2012), blueshifted and time-varying Na I or K I absorption features (e.g., Patat et al 2007;Simon et al 2009;Fox & Filippenko 2013;Sternberg et al 2014;Graham et al 2015), and the imbalance between the blue-and redshifted Na I absorption components (Sternberg et al 2011;Foley et al 2012;Maguire et al 2013;Phillips et al 2013).…”

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

“…Dust along the line of sight toward SNe Ia absorbs, scatters, and polarizes the SNe radiation in the UV-NIR wavelength range (see, e.g., Hoang 2017). Photometric observations of SNe Ia show that the total-to-selective extinction ratio R V = A V /E(B − V ), with A V the optical extinction and E(B − V ) = A B − A V the color excess, is much lower than the typical value of interstellar dust in the Milky Way of R V ∼ 3.1.…”

Properties of interstellar dust responsible for extinction laws with unusually low total-to-selective extinction ratios of R=1−2

“…The extensive observations have revealed that the extinction curve derived for SN 2014J is highly steep with a very low value of R V ≃ 1.5 (e.g., Goobar et al, 2014;Amanullah et al, 2014;Foley et al, 2014;Marion et al, 2015). From a simultaneous fit to the extinction and polarization data, Hoang (2015) claim that both interstellar and circumstellar dust are responsible for the anomalous extinction property toward SN 2014J. However, the time invariability of the color (Brown et al, 2015) and polarization (Kawabata et al, 2014;Patet et al, 2015) indicates that its peculiar extinction is mainly of interstellar-dust origin.…”