A Spectropolarimetric Comparison of the Type II-Plateau Supernovae SN 2008bk and SN 2004dj
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Fecha
2011
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Facultad/escuela
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en
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Resumen
The Type II-Plateau supernova (SN II-P) SN 2004dj was the first SN II-P for which
spectropolarimetry
data were obtained with fine temporal sampling before, during, and after its fall off of the
photometric plateau – the point that marks the transition from the photospheric to the nebular phase in
SNe II-P. Unpolarized during the plateau, SN 2004dj showed a dramatic spike in polarization during the
descent off of the plateau, and then exhibited a smooth polarization decline over the next two
hundred days. This behavior was interpreted by Leonard et al. (2006) as evidence for a strongly
non-spherical explosion mechanism that had imprinted asphericity only in the innermost ejecta. In this brief
report, we compare nine similarly well-sampled epochs of spectropolarimetry of the Type II-P SN
2008bk to those of SN 2004dj. In contrast to SN 2004dj, SN 2008bk became polarized well before the end
of the plateau and also retained a nearly constant level of polarization through the early nebular
phase. Curiously, although the onset and persistence of polarization differ between the
two objects, the detailed spectropolarimetric characteristics at the epochs of recorded maximum
polarization for the two objects are extremely similar, feature by feature. We briefly interpret the
data in light of non-Local-Thermodynamic Equilibrium, time-dependent radiative-transfer simulations
specifically crafted for SN II-P ejecta.
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Palabras clave
Supernovae, Individual (SN 2004dj, SN 2008bk), Techniques: polarimetric PACS: 97.60.Bw, 97.10.Ld