Spectropolarimetry of the Type IIb SN 2008aq

TL;DR

This study presents optical spectropolarimetry of the Type IIb supernova 2008aq, revealing its spectral evolution, polarization levels, and asymmetries, providing insights into its progenitor's structure and explosion geometry.

Contribution

It provides the first detailed spectropolarimetric analysis of SN 2008aq, highlighting its spectral transition and asymmetry features compared to other Type IIb supernovae.

Findings

Helium features increased over time, indicating transition from Type IIb to Ib.

Continuum polarization levels increased from 0.70% to 1.21%.

Loops in q-u plane suggest departure from axial symmetry.

Abstract

We present optical spectroscopy and spectropolarimetry of the Type IIb SN 2008aq 16 days and 27 days post-explosion. The spectrum of SN 2008aq remained dominated by Halpha P Cygni profile at both epochs, but showed a significant increase in the strength of the helium features, which is characteristic of the transition undergone by supernovae between Type IIb and Type Ib. Comparison of the spectra of SN 2008aq to other Type IIb SNe (SN 1993J, SN 2011dh, and SN 2008ax) at similar epochs revealed that the helium lines in SN 2008aq are much weaker, suggesting that its progenitor was stripped to a lesser degree. SN 2008aq also showed significant levels of continuum polarisation at p_cont = 0.70 (+/- 0.22) % in the first epoch, increasing to p_cont = 1.21 (+/- 0.33) % by the second epoch. Moreover, the presence of loops in the q-u planes of Halpha and He I in the second epoch suggests a departure from axial symmetry.