Coronal lines and dust formation in SN 2005ip: Not the brightest, but the hottest Type IIn supernova

TL;DR

SN2005ip, a Type IIn supernova, exhibited unique coronal lines and dust formation in both ejecta and post-shock gas, revealing complex CSM interaction and dust processes over three years.

Contribution

This study provides the first detailed optical photometry and spectroscopy of SN2005ip over three years, highlighting unprecedented coronal lines and evidence of dust formation in multiple regions.

Findings

Presence of high-ionization coronal lines in late spectra

Evidence of dust formation in both ejecta and post-shock gas

Rejuvenated CSM interaction with clumpy stellar wind

Abstract

We present optical photometry and spectroscopy of SN2005ip for the first 3yr after discovery, showing an underlying Type II-L SN interacting with a steady wind to yield an unusual Type IIn spectrum. For the first 160d, it had a fast linear decline from a modest peak absolute magnitude of about -17.4 (unfiltered), followed by a plateau at roughly -14.8 for more than 2yr. Initially having a normal broad-lined spectrum superposed with sparse narrow lines from the photoionized CSM, it quickly developed signs of strong CSM interaction with a spectrum similar to that of SN1988Z. As the underlying SNII-L faded, SN2005ip exhibited a rich high-ionization spectrum with a dense forest of narrow coronal lines, unprecedented among SNe but reminiscent of some active galactic nuclei. The line-profile evolution of SN 2005ip confirms that dust formation caused its recently reported infrared excess, but these lines reveal that it is the first SN to show clear evidence for dust in both the fast SN ejecta and the slower post-shock gas. SN2005ip's complex spectrum confirms the origin of the strange blue continuum in SN2006jc, which also had post-shock dust formation. We suggest that SN2005ip's late-time plateau and coronal spectrum result from rejuvenated CSM interaction between a sustained fast shock and a clumpy stellar wind, where X-rays escape through the optically thin interclump regions to heat the pre-shock CSM to coronal temperatures.