Spectropolarimetry of Type II supernovae

Nagao, Takashi; Mattila, S.; Kotak, R.; Kuncarayakti, H.

doi:10.1051/0004-6361/202346713

Cited by 3 publications

(2 citation statements)

References 71 publications

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“…The spectropolarimetric observations and their analysis are similar to those reported in Nagao et al (2023). We observed SN 2021yja using the low-resolution G300V grism and a halfwave retarder plate (HWP) with the optimal set of HWP angles of 0 • , 22.5 • , 45 • , and 67.5 • .…”

Section: Observationssupporting

confidence: 59%

“…When calculating the polarization degrees, we subtracted the polarization bias, following Wang et al (1997). As the polarization degrees on the Hα emission line -where the intrinsic polarization is supposed to be depolarized and thus the interstellar polarization (ISP) should be dominant (e.g., Nagao et al 2023)-are close to zero, we assume that the ISP in SN 2021yja is negligibly small, which is also adopted by Vasylyev et al (2024).…”

Section: Observationsmentioning

confidence: 99%

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Evidence for bipolar explosions in Type IIP supernovae

Nagao,

Maeda,

Mattila

et al. 2024

A&A

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Recent observations of core-collapse supernovae (SNe) suggest aspherical explosions. Globally, aspherical structures in SN explosions are thought to encode information regarding the underlying explosion mechanism. However, the exact explosion geometries from the inner cores to the outer envelopes are poorly understood. Here, we present photometric, spectroscopic, and polarimetric observations of the Type IIP SN 2021yja and discuss its explosion geometry in comparison to those of other Type IIP SNe that show large-scale aspherical structures in their hydrogen envelopes (SNe 2012aw, 2013ej and 2017gmr). During the plateau phase, SNe 2012aw and 2021yja exhibit high continuum polarization characterized by two components with perpendicular polarization angles. This behavior can be interpreted as being due to a bipolar explosion, where the SN ejecta is composed of a polar (energetic) component and an equatorial (bulk) component. In such a bipolar explosion, an aspherical axis created by the polar ejecta would dominate at early phases, while the perpendicular axis along the equatorial ejecta would emerge at late phases after the photosphere in the polar ejecta has receded. Our interpretation of the explosions in SNe 2012aw and 2021yja as bipolar is also supported by other observational properties, including the time evolution of the line velocities and the line shapes in the nebular spectra. The polarization of other Type IIP SNe that show large-scale aspherical structures in the hydrogen envelope (SNe 2013ej and 2017gmr) is also consistent with the bipolar-explosion scenario, although this is not conclusive.

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Section: Observationssupporting

confidence: 59%

Section: Observationsmentioning

confidence: 99%

Evidence for bipolar explosions in Type IIP supernovae

Nagao,

Maeda,

Mattila

et al. 2024

A&A

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Spectropolarimetry of Type II supernovae

Nagao,

Patat,

Cikota

et al. 2024

A&A

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The explosion processes of supernovae (SNe) are imprinted in their explosion geometries. The recent discovery of several highly aspherical core-collapse SNe is significant, and studying these is regarded as being crucial in order to understand the underlying explosion mechanism. Here, we study the intrinsic polarization of 15 hydrogen-rich core-collapse SNe and explore the relation between polarization and the photometric and spectroscopic properties of these objects. Our sample shows diverse properties of the continuum polarization. Most SNe show a low degree of polarization at early phases but a sudden rise to ∼1% at certain points during the photospheric phase followed by a slow decline during the tail phase, with a constant polarization angle. The variation in the timing of peak polarization values implies diversity in the explosion geometry: some SNe have aspherical structures only in their helium cores, while in other SNe such structures reach out to a significant part of the outer hydrogen envelope with a common axis from the helium core to the hydrogen envelope. Other SNe show high polarization from early phases and a change in polarization angle around the middle of the photospheric phase. This implies that the ejecta are significantly aspherical out to the outermost layer and have multi-directional aspherical structures. Exceptionally, the Type IIL SN 2017ahn shows low polarization at both the photospheric and tail phases. Our results show that the timing of the polarization rise in Type IIP SNe is likely correlated with their brightness, velocity, and the amount of radioactive Ni produced: brighter SNe with faster ejecta velocity and a larger 56Ni mass have more extended aspherical explosion geometries. In particular, there is a clear correlation between the timing of the polarization rise and the explosion energy; that is, the explosion asphericity is proportional to the explosion energy. This implies that the development of a global aspherical structure, such as a jet, might be the key for the realisation of an energetic SN in the mechanism of SN explosions.

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Intermediate-luminosity Type IIP SN 2021gmj: a low-energy explosion with signatures of circumstellar material

Murai,

Tanaka,

Kawabata

et al. 2024

Monthly Notices of the Royal Astronomical Society

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We present photometric, spectroscopic and polarimetric observations of the intermediate-luminosity Type IIP supernova (SN) 2021gmj from 1 to 386 days after the explosion. The peak absolute V-band magnitude of SN 2021gmj is −15.5 mag, which is fainter than that of normal Type IIP SNe. The spectral evolution of SN 2021gmj resembles that of other sub-luminous supernovae: the optical spectra show narrow P-Cygni profiles, indicating a low expansion velocity. We estimate the progenitor mass to be about 12 $\rm M_{\odot }$ from the nebular spectrum and the 56Ni mass to be about 0.02 $\rm M_{\odot }$ from the bolometric light curve. We also derive the explosion energy to be about 3 × 1050 erg by comparing numerical light curve models with the observed light curves. Polarization in the plateau phase is not very large, suggesting nearly spherical outer envelope. The early photometric observations capture the rapid rise of the light curve, which is likely due to the interaction with a circumstellar material (CSM). The broad emission feature formed by highly-ionized lines on top of a blue continuum in the earliest spectrum gives further indication of the CSM at the vicinity of the progenitor. Our work suggests that a relatively low-mass progenitor of an intermediate-luminosity Type IIP SN can also experience an enhanced mass loss just before the explosion, as suggested for normal Type IIP SNe.

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Spectropolarimetry of Type II supernovae

Cited by 3 publications

References 71 publications

Evidence for bipolar explosions in Type IIP supernovae

Evidence for bipolar explosions in Type IIP supernovae

Spectropolarimetry of Type II supernovae

Intermediate-luminosity Type IIP SN 2021gmj: a low-energy explosion with signatures of circumstellar material

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