To read:
\citet{Mauerhan_2017}: SN 2013ej
Review papers:
\citet{Wang_2008}: Spectropolarimetry of Supernovae
This is a very observation oriented review covering specpol of both Ia and CCSNe. It has an exhaustive list of all SNe with polarimetric observations, both photometric and spectroscopic. For CC, it went through all the subtypes, and conclude that all CCSNe are significantly polarized. The common II-P events have small polarization during the plateau then experience a jump in polarization as the SN enters the nebular phase. The interpretation for this observation is that the asymmetric inner core region is revealed. The best observation of this is from SN 2004dj (Leonard+ 2006). This interpretation is corroborated by the fact that IIb and Ib/c are polarized early on since the core is already revealed, although observations for these are sparse.
Morphology of the polarimetric spectra on the qu plane can be helpful. Recall that the angle of polarization is 0.5 arctan(u/q), so if a SN is axisymmetric, its specpol will fall into a line in the qu plane (constant PA, thus constant u/q). Any scatter perpendicular to that is a sign of deviation from axisymmetry. Varying PA across a line can produce a loop in the qu plane.
\citet{Mauerhan_2015}
IIn
\citet{Reilly_2017} FORS2 Optical specpol for SN 2009ip during the 2012 outbursts.
About SN 2009ip
- First detected in 2009 August, before reclassified as an LBV outburst
- Preexplosion HST image -> 50-60 solar mass start
- Two spectacular outbursts in 2012, July 24 at M = -14 and Sep 23 at M = -18.5
- The 2012b outburst is believed to be terminal, but it's still under debate.
Polarimetric observations by FORS2 on the VLT, 35, 42, 64, 68, 73, and 83 days after the 2012b outburst
- ISP determined by assuming that the core of H\(\alpha\) emission line is unpolarized since the opacity is high and the emission comes from outside.
- Continuum polarization (bands without lines): 0.7% at 45\(^{\circ}\) at 35-64d, then ~60\(^{\circ}\) rotation around ~70d, which is also when the bolometric lightcurve dips. (Though they didn't say why)
- Broad line polarization, focused on H\(\alpha\): depolarization (found by removing continuum contribution by fitting 2nd order polynomial to cont. flux to then remove cont. polarization)
- Low-velocity narrow lines polarization (low v = not far from main peak): H\(\alpha\), \(\beta\) and He I have absorption component at -1500 km/s. Generally 0.5-1% polarized at 30-40\(^{\circ}\). All lines seem to come from the same line forming region.
- Intermediate and high-velocity narrow lines polarization: similar degree of polarization, but different angle (~100-120\(^{\circ}\)). Lines at similar velocity from different lines share similar polarimetry, again, these share the same line forming region, which is different from the low velocity one.
Interpretation of polarimetry
II-P