Broad-band polarimetric investigation of the Type II-plateau supernova 2013ej

Abstract

We present results based on follow-up observations of the Type II-plateau supernova (SN) 2013ej at 6 epochs spanning a total duration of ∼37 d. The R c -band linear polarimetric observations were carried out between the end of the plateau and the beginning of the nebular phases as noticed in the photometric light curve. The contribution due to interstellar polarization (ISP) was constrained by using couple of approaches, i.e. based upon the observations of foreground stars lying within 5 ′ and 10• radius of the SN location and also investigating the extinction due to the Milky Way and host galaxy towards the SN direction. Our analysis revealed that in general the intrinsic polarization of the SN is higher than the polarization values for the foreground stars and exhibits an increasing trend during our observations. After correcting the ISP of ∼0.6 per cent, the maximum intrinsic polarization of SN 2013ej is found to be 2.14 ± 0.57 per cent. Such a strong polarization has rarely been seen in Type II-P SNe. If this is the case, i.e., the 'polarization bias' effect is still negligible, the polarization could be attributed to the asymmetry of the inner ejecta of the SN because the ISP towards the SN location is estimated to be, at most, 0.6 per cent.

Unifying Type II Supernova Light Curves with Dense Circumstellar Material

“…6 Broadband polarimetric analysis of the late (>100 days) phase of this SN performed by Kumar et al (2016) also shows unusually strong intrinsic polarization of up to 2.14%. This could be a signal of possible asymmetry in the ejecta, or could arise due to scattering of the SN light by a dusty CSM(e.g., Wang & Wheeler 1996).…”

Asphericity, Interaction, and Dust in the Type Ii-P/Ii-L Supernova 2013ej in Messier 74

“…The dust-scattering mode appears to become more influential in our last epoch at the end of the recombination phase (day 107), based on the increased amount of residual polarization for the Hα emission peak and on the reasonable match of our model. The continued increase in fractional polarization indicated by the late-time imaging polarimetry from Kumar et al (2016) could indicate that scattering by circumstellar dust continues beyond day 130, or that the asphericity in the inner electron-scattering environment becomes even more pronounced.…”

“…Narrowing the sample to four ISP probe stars within ¢ 5 of the SN, and after removing those that exhibited evidence for polarimetric variability, Kumar et al (2016) …”

“…As the light-curve plateau drops down to the radioactive decay tail, the continuum P also drops by several tenths of a percent, while θ shifts~ 14 back toward the values measured on day 73 and earlier. Figure 3 (right panel) shows the same data after subtracting the slightly larger value of ISP derived by Kumar et al (2016). As described in Section 2.3, we adopted their R-band ISP value and scaled to the V-band and continuum regions according to the functional form of Serkowski et al (1975) and Whittet et al (1992).…”

“…As described in Section 2.3, we adopted their R-band ISP value and scaled to the V-band and continuum regions according to the functional form of Serkowski et al (1975) and Whittet et al (1992). The R-band imaging polarimetry measurements from Kumar et al (2016) are also included in Figure 3 for comparison. We note that their first two epochs of polarimetry near day 100 are significantly below the persistently high polarization trend exhibited by our data, although the error bars associated with their second epoch overlap with our inferred trend.…”