Keywords

Type Ia supernovae (SNe Ia) are powerful cosmological "standardizable candles" and the most precise distance indicators. However, a limiting factor in their use for precision cosmology rests on our ability to correct for the dust extinction toward them. SN 2014J in the starburst galaxy M82, the closest detected SN Ia in three decades, provides unparalleled opportunities to study the dust extinction toward an SN Ia. In order to derive the extinction as a function of wavelength, we model the color excesses toward SN 2014J, which are observationally derived over a wide wavelength range, in terms of dust models consisting of a mixture of silicate and graphite. The resulting extinction laws steeply, rise toward the far-ultraviolet, even steeper than that of the SMC. We infer a visual extinction of ${A}_{V}\approx 1.9\;\mathrm{mag}$, a reddening of $E(B-V)\approx 1.1\;\mathrm{mag}$, and a total-to-selective extinction ratio of R_V $\approx$ 1.7, consistent with that previously derived from photometric, spectroscopic, and polarimetric observations. The size distributions of the dust in the interstellar medium toward SN 2014J are skewed toward substantially smaller grains than that of the Milky Way and the SMC.

We present optical and near-infrared multi-band linear polarimetry of the highly reddened Type Ia supernova (SN) 2014J that appeared in M82. SN 2014J exhibits large polarization at shorter wavelengths, e.g., 4.8% in the B band, which decreases rapidly at longer wavelengths, while the position angle of the polarization remains at approximately 40° over the observed wavelength range. These polarimetric properties suggest that the observed polarization is likely predominantly caused by the interstellar dust within M82. Further analysis shows that the polarization peaks at a wavelengths much shorter than those obtained for the Galactic dust. The wavelength dependence of the polarization can be better described by an inverse power law rather than by the Serkowski law for Galactic interstellar polarization. These points suggest that the nature of the dust in M82 may be different from that in our Galaxy, with polarizing dust grains having a mean radius of <0.1 μm.

The wavelength dependence of the extinction of Type Ia SN 2014J in the nearby galaxy M82 has been measured using UV to near-IR photometry obtained with the Hubble Space Telescope, the Nordic Optical Telescope, and the Mount Abu Infrared Telescope. This is the first time that the reddening of an SN Ia is characterized over the full wavelength range of 0.2–2 μm. A total-to-selective extinction, R_V ⩾ 3.1, is ruled out with high significance. The best fit at maximum using a Galactic type extinction law yields R_V = 1.4 ± 0.1. The observed reddening of SN 2014J is also compatible with a power-law extinction, A_λ/A_V = (λ/λ_V)^p as expected from multiple scattering of light, with p = −2.1 ± 0.1. After correcting for differences in reddening, SN 2014J appears to be very similar to SN 2011fe over the 14 broadband filter light curves used in our study.

We report on the discovery of SN 2014J in the nearby galaxy M82. Given its proximity, it offers the best opportunity to date to study a thermonuclear supernova (SN) over a wide range of the electromagnetic spectrum. Optical, near-IR, and mid-IR observations on the rising light curve, orchestrated by the intermediate Palomar Transient Factory, show that SN 2014J is a spectroscopically normal Type Ia supernova (SN Ia), albeit exhibiting high-velocity features in its spectrum and heavily reddened by dust in the host galaxy. Our earliest detections start just hours after the fitted time of explosion. We use high-resolution optical spectroscopy to analyze the dense intervening material and do not detect any evolution in the resolved absorption features during the light curve rise. Similar to other highly reddened SNe Ia, a low value of total-to-selective extinction, R_V ≲ 2, provides the best match to our observations. We also study pre-explosion optical and near-IR images from Hubble Space Telescope with special emphasis on the sources nearest to the SN location.