Evidence of Asymmetry in SN 2007rt, a Type IIn Supernova

TL;DR

This study presents optical observations of SN 2007rt, revealing asymmetries, dense circumstellar interaction, and evidence of dust formation, suggesting a high He/H progenitor star with asymmetric mass-loss history.

Contribution

It provides detailed spectroscopic and photometric analysis of SN 2007rt, highlighting asymmetries and unique spectral features not commonly seen in Type IIn supernovae.

Findings

Presence of dense circumstellar medium interacting with ejecta

Detection of broad He I 5875 line indicating high He/H ratio

Evidence of newly formed dust at late times

Abstract

An optical photometric and spectroscopic analysis of the slowly-evolving Type IIn SN2007rt is presented, covering a duration of 481 days after discovery. Its earliest spectrum, taken approximately 100 days after the explosion epoch, indicates the presence of a dense circumstellar medium, with which the supernova ejecta is interacting. This is supported by the slowly-evolving light curve. A notable feature in the spectrum of SN 2007rt is the presence of a broad He I 5875 line, not usually detected in Type IIn supernovae. This may imply that the progenitor star has a high He/H ratio, having shed a significant portion of its hydrogen shell via mass-loss. An intermediate resolution spectrum reveals a narrow Halpha P-Cygni profile, the absorption component of which has a width of 128 km/s. This slow velocity suggests that the progenitor of SN 2007rt recently underwent mass-loss with wind speeds comparable to the lower limits of those detected in luminous blue variables. Asymmetries in the line profiles of H and He at early phases bears some resemblance to double-peaked features observed in a number of Ib/c spectra. These asymmetries may be indicative of an asymmetric or bipolar outflow or alternatively dust formation in the fast expanding ejecta. In addition, the late time spectrum, at over 240 days post-explosion, shows clear evidence for the presence of newly formed dust.