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Researchers analyzed the Type Ic broad-line supernova 2026gzf using polarimetry techniques at two time points following its X-ray detection by the Einstein Probe satellite. They found that while the supernova's outer layers maintained a mostly spherical shape, the distribution of calcium and oxygen-burning products revealed an axisymmetric internal structure with a preferred axis. By modeling the observations, they determined the supernova is likely being viewed at approximately 40 degrees from this symmetry axis, providing direct insight into the three-dimensional geometry of the explosion.
Why it matters
This work helps constrain the explosion mechanisms of energetic supernovae by revealing their three-dimensional structure through polarization measurements. Understanding the geometry of these explosions is crucial for interpreting high-energy transient events and comprehending how massive stars end their lives.
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⚠️ Preprint – Noch nicht peer-reviewed
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Abstract: Type Ic broad-line supernovae (SNe Ic-BL) are often associated with energetic explosions that display a prompt outburst of high-energy emission. Since their progenitor lost the H and He envelopes before the explosion exposing the C/O core, their explosion dynamics and geometry can be seen in an unobscured and undistorted way. We present imaging polarimetry and spectropolarimetry of the Type Ic-BL SN 2026gzf obtained 4.6 and 16.5 days after the X-ray shock breakout, which was recorded by the Einstein Probe satellite as EP260321a, showing it to be one of the softest and intrinsically dimmest extragalactic fast X-ray transients. The persistent low continuum polarization indicates that the outer layer of SN 2026gzf is mostly spherical, suggesting the explosion did not significantly disrupt the progenitor envelope. At day 16.5, the calcium near-infrared triplet displays a peak polarization above 1.5%. The geometry of the associated line opacity is also compatible with an axisymmetric configuration. The spatial distribution of such oxygen-burning ashes thus indicates the presence of a symmetry axis of the excitation structure within the nearly spherical ejecta. The Ca II triplet profile is dominated by a primary component spanning ~25,000–40,000 km/s, alongside a distinct secondary component extending above 28,000 km/s whose polarization implies a non-axisymmetric, complex excitation geometry toward the outer ejecta By implementing a three-dimensional Monte-Carlo calculation, we infer that a viewing angle of ~40 degree from the symmetry axis of the excitation structure could plausibly reproduce the observed spectral and polarization profiles of the Ca II triplet.
Source: Pinning Down the Geometry of the Type Ic Broad-Line Supernova 2026gzf