DEVIATIONS FROM AXISYMMETRY REVEALED BY LINE POLARIZATION IN THE NORMAL TYPE Ia SUPERNOVA 2004S

Spectropolarimetry is one of the most powerful methods to study the multi-dimensional geometry of extragalactic supernovae (SNe). We have performed spectropolarimetric observations of Type Ib/c SNe with the Subaru telescope. The data clearly show the "loop" in the Stokes Q − U plane. By performing 3D radiative transfer simulations, we show that the loop is clear evidence for 3D, non-axisymmetric geometry of SNe. We also summarize the properties of the line polarization of Type Ib/c SNe. We find that a stronger line tends to show a higher line polarization. This effect must be corrected to compare the polarization of different lines or different objects.

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“…Fig. 1, and as suggested by these authors [3,4,5,6,7,8], this loop clearly indicates that these SNe have 3D, non-axisymmetric geometry.…”

Section: Introductionsupporting

confidence: 78%

Subaru spectropolarimetry of supernovae

Tanaka

Kawabata

Hattori

et al. 2012

AIP Conference Proceedings

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“…There is a correlation between the velocity gradient and the Si ii line polarization (Leonard et al 2005; Chornock & Filippenko 2008; Maund et al 2010). This may indicate that the viewing direction is indeed controlling the line polarization level, if the velocity gradient is determined by the viewing angle effect (M10b).…”

Section: Discussionmentioning

confidence: 99%

Effects of the explosion asymmetry and viewing angle on the Type Ia supernova colour and luminosity calibration★

Maeda

Leloudas

Taubenberger

et al. 2011

Monthly Notices of the Royal Astronomical Society

126

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Phenomenological relations exist between the peak luminosity and other observables of type Ia supernovae (SNe Ia) that allow one to standardize their peak luminosities. However, several issues are yet to be clarified: SNe Ia show colour variations after the standardization. Also, individual SNe Ia can show residuals in their standardized peak absolute magnitude at the level of ∼0.15 mag. In this paper, we explore how the colour and luminosity residual are related to the wavelength shift of nebular emission lines observed at ≳150 d after the maximum light. A sample of 11 SNe Ia which likely suffer from little host extinction indicates a correlation (3.3σ) between the peak B−V colour and the late‐time emission‐line shift. Furthermore, a nearly identical relation applies for a larger sample in which only three SNe with B−V≳ 0.2 mag are excluded. Following the interpretation that the late‐time emission‐line shift is a tracer of the viewing direction from which an off‐centre explosion is observed, we suggest that the viewing direction is a dominant factor controlling the SN colour and that a large part of the colour variations is intrinsic, rather than due to the host extinction. We also investigate a relation between the peak luminosity residuals and the wavelength shift in nebular emission lines in a sample of 20 SNe. We thereby found a hint of a correlation (at ∼1.6σ level). The confirmation of this will require a future sample of SNe with more accurate distance estimates. Radiation transfer simulations for a toy explosion model where different viewing angles cause the late‐time emission‐line shift are presented, predicting a strong correlation between the colour and shift, and a weaker one for the luminosity residual.

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“…Given a common origin of the HV absorption from the aspherical ejecta (e.g., a torus or clumps), the diversity in strength of the HV features could be interpreted as a line-of-sight effect (see also Tanaka et al 2006). Aspherical structure of the ejecta is favored by the evidence that the degree of polarization for the line features in SN 2001el is much higher than that for the continuum (Wang et al 2003b;Kasen et al 2003; see also Chornock & Filippenko 2008. It is thus interesting to examine whether the strength of the HV line features correlates, at least for a subset of SNe Ia, with that of the line polarization.…”

Section: Discussionmentioning

confidence: 99%

THE GOLDEN STANDARD TYPE Ia SUPERNOVA 2005cf: OBSERVATIONS FROM THE ULTRAVIOLET TO THE NEAR-INFRARED WAVEBANDS

Wang

Filippenko

et al. 2009

ApJ

161

160

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We present extensive photometry at ultraviolet (UV), optical, and near-infrared (NIR) wavelengths, as well as dense sampling of optical spectra, for the normal Type Ia supernova (SN Ia) 2005cf. The optical photometry, performed at eight different telescopes, shows a 1σ scatter of 0.03 mag after proper corrections for the instrument responses. From the well-sampled light curves, we find that SN 2005cf reached a B-band maximum at 13.63 ± 0.02 mag, with an observed luminosity decline rate Δm 15 (B) = 1.05 ± 0.03 mag. The correlations between the decline rate and various color indexes, recalibrated on the basis of an expanded SN Ia sample, yield a consistent estimate for the host-galaxy reddening of SN 2005cf, E(B − V ) host = 0.10 ± 0.03 mag. The UV photometry was obtained with the Hubble Space Telescope and the Swift Ultraviolet/Optical Telescope, and the results match each other to within 0.1-0.2 mag. The UV light curves show similar evolution to the broadband U, with an exception in the 2000-2500 Å spectral range (corresponding to the F220W/uvm2 filters), where the light curve appears broader and much fainter than that on either side (likely owing to the intrinsic spectral evolution). Combining the UV data with the ground-based optical and NIR data, we establish the generic UVoptical-NIR bolometric light curve for SN 2005cf and derive the bolometric corrections in the absence of UV and/or NIR data. The overall spectral evolution of SN 2005cf is similar to that of a normal SN Ia, but with variety in the strength and profile of the main feature lines. The spectra at early times displayed strong, high-velocity (HV) features in the Ca ii H&K doublet and NIR triplet, which were distinctly detached from the photosphere (v ≈ 10,000 km s −1 ) at a velocity ranging from 20,000 to 25,000 km s −1 . One interesting feature is the flatbottomed absorption observed near 6000 Å in the earliest spectrum, which rapidly evolved into a triangular shape and then became a normal Si ii λ6355 absorption profile at about one week before maximum brightness. This premaximum spectral evolution is perhaps due to the blending of the Si iiλ6355 at photospheric velocity and another HV absorption component (e.g., an Si ii shell at a velocity ∼18,000 km s −1 ) in the outer ejecta, and may be common in other normal SNe Ia. The possible origin of the HV absorption features is briefly discussed.

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DEVIATIONS FROM AXISYMMETRY REVEALED BY LINE POLARIZATION IN THE NORMAL TYPE Ia SUPERNOVA 2004S

Cited by 25 publications

References 57 publications

Subaru spectropolarimetry of supernovae

Subaru spectropolarimetry of supernovae

Effects of the explosion asymmetry and viewing angle on the Type Ia supernova colour and luminosity calibration★

THE GOLDEN STANDARD TYPE Ia SUPERNOVA 2005cf: OBSERVATIONS FROM THE ULTRAVIOLET TO THE NEAR-INFRARED WAVEBANDS

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