Evidence for multiple origins of fast declining Type II supernovae from spectropolarimetry of SN 2013ej and SN 2017ahn

ABSTRACT The origin of the diverse light-curve shapes Type II supernovae (SNe), and whether they come from similar or distinct progenitors, has been actively discussed for decades. Here, we report spectropolarimetry two fast declining (Type IIL) SNe: SN 2013ej 2017ahn. exhibited high continuum polarization very soon after explosion to radioactive tail phase with time-variable angles. this polarimetric behaviour can be interpreted as combination different aspherical structures, namely an interaction ejecta circumstellar matter (CSM) inherently explosion. Aspherical explosions are a common feature slowly IIP) SNe. By contrast, 2017ahn showed low not only in photospheric but also phase. This phase, which never before observed other IIP/L SNe, suggests that was nearly spherical. These observations imply IIL SNe have, at least, origins: result stars have properties and/or mass-loss processes. fact might indicate 13ej-like originate progenitor those IIP accompanied by CSM interaction, while 17ahn-like more massive less hydrogen its envelope.