SN2013fs and SN2013fr: Exploring the circumstellar-material diversity in Type II supernovae

TL;DR

This study analyzes two Type II supernovae, SN2013fs and SN2013fr, revealing diverse circumstellar material interactions that suggest a continuum between SNe IIn, II-L, and II-P, with implications for pre-supernova mass loss.

Contribution

It provides detailed photometric and spectroscopic observations of SN2013fs and SN2013fr, demonstrating the diversity of CSM interaction and proposing a continuum among different Type II supernovae.

Findings

SN2013fs showed early CSM interaction with dense material close to the progenitor.

SN2013fr transitioned from a SNIIn to a SNII-L, indicating variable CSM influence.

Both supernovae exhibited signs of pre-SN mass loss and dust formation.

Abstract

We present photometry and spectroscopy of SN2013fs and SN2013fr in the first 100 days post-explosion. Both objects showed transient, relatively narrow H$\alpha$ emission lines characteristic of SNeIIn, but later resembled normal SNeII-P or SNeII-L, indicative of fleeting interaction with circumstellar material (CSM). SN2013fs was discovered within 8hr of explosion. Its light curve exhibits a plateau, with spectra revealing strong CSM interaction at early times. It is a less luminous version of the transitional SNIIn PTF11iqb, further demonstrating a continuum of CSM interaction intensity between SNeII-P and IIn. It requires dense CSM within 6.5$\times$10$^{14}$~cm of the progenitor, from a phase of advanced pre-SN mass loss shortly before explosion. Spectropolarimetry of SN2013fs shows little continuum polarization, but noticeable line polarization during the plateau phase. SN2013fr morphed from a SNIIn at early times to a SNII-L. After the first epoch its narrow lines probably arose from host-galaxy emission, but the bright, narrow H$\alpha$ emission at early times may be intrinsic. As for SN2013fs, this would point to a short-lived phase of strong CSM interaction if proven to be intrinsic, suggesting a continuum between SNeIIn and II-L. It is a low-velocity SNII-L, like SN2009kr but more luminous. SN2013fr also developed an IR excess at later times, due to warm CSM dust that require a more sustained phase of strong pre-SN mass loss.