Asymmetries in the type IIn SN 2010jl

Abstract

Aims. We study possible signs of asymmetry in the luminous type IIn SN 2010jl, to obtain independent information about its explosion geometry. Methods. We performed optical linear spectropolarimetry of SN 2010jl two weeks after the discovery, in the spectral range 3700-8800 Å.Results. The object exhibits a continuum polarization at a very significant and almost constant level (1.7-2.0%). Distinctive line depolarization is seen at the positions of the strongest emission features, such as Hα and Hβ. This implies that the line forming region is well above the photosphere. The continuum polarization level (1.7-2.0%) indicates a substantial asphericity, of axial ratio ≤0.7. The almost complete depolarization seen at Hα is indicative of a very low level of interstellar polarization (≤0.3%). This rules out the presence of relevant amounts of dust in the progenitor environment at the time of our observations. From a polarimetric point of view, SN 2010jl appears to be very similar to the two other well-studied type IIn SNe 1997eg and 1998S, establishing a strong link between members of this class of objects.

Numerical simulations of superluminous supernovae of type IIn

“…Our results for a prolate morphology with a pole-to-equator density ratio of ∼ 3 yield a maximum ∼ < 2% continuum polarisation compatible with the value observed for SN 2010jl (Patat et al 2011). In this context, the asymmetry may stem only from the CSM, although both inner and outer shells may be asymmetric.…”

“…Along this direction, the continuum polarisation has its maximum value, reaching about 1.6% for A1 = 1.6. As we progress towards the Hα rest wavelength from continuum regions (i.e., ∼ > 3000 km s −1 from line centre), the polarisation decreases steadily, as observed in SN 2010jl (Patat et al 2011;Williams et al 2014) and in some Wolf-Rayet Figure 16. left: Illustration of the wavelength (λ) and depth (R) dependence of the quantity R>R 15 δF (R, λ), where δF (R, λ) = (2π/D 2 ) ∆R ∆z η(p, z, λ) e −τ (p,z,λ) pdp, and R 15 is R in units of 10 15 cm.…”

“…(Patat et al 2011), which is within a few days of our model time (left panel). In the context of our model, the observed polarisation may be interpreted as arising from a prolate CSM with a pole-to-equator density ratio of ∼ 3.…”

“…There is, however, observational evidence from spectropolarimetric observations that some SNe IIn are asymmetric on large scale (Leonard et al 2000;Wang et al 2001;Hoffman et al 2008;Patat et al 2011). This we try to address in this section by performing 2-D polarisation calculations.…”

“…Two good examples of such SNe IIn are SN 2006gy ) and more recently SN 2010jl (Stoll et al 2011). The latter has extensive photometric and spectroscopic observations (Stoll et al 2011;Zhang et al 2012;Ofek et al 2014;Fransson et al 2014) and also has spectropolarimetric data (Patat et al 2011;Williams et al 2014). How stars produce the outer shell is unclear -it may be material ejected by the pair-production instability (Barkat et al 1967;Woosley et al 2007) or it may be material ejected via a superEddington wind (Owocki et al 2004).…”