SN 2015ba: A type IIP supernova with a long plateau

TL;DR

SN 2015ba is a luminous Type IIP supernova with an unusually long plateau, providing insights into massive progenitors and circumstellar interaction through detailed photometric and spectroscopic analysis.

Contribution

This study presents comprehensive photometry, spectroscopy, and modeling of SN 2015ba, revealing its long plateau and challenging existing correlations between progenitor mass and oxygen core mass.

Findings

Long 123-day plateau observed in SN 2015ba

High-velocity H-Balmer components suggest circumstellar interaction

Nebular spectra show low oxygen levels despite massive progenitor

Abstract

We present optical photometry and spectroscopy from about a week after explosion to $\sim$272 d of an atypical Type IIP supernova, SN 2015ba, which exploded in the edge-on galaxy IC 1029. SN 2015ba is a luminous event with an absolute V-band magnitude of -17.1$\pm$0.2 mag at 50 d since explosion and has a long plateau lasting for $\sim$123 d. The distance to the SN is estimated to be 34.8$\pm$0.7 Mpc using the expanding photosphere and standard candle methods. High-velocity H-Balmer components constant with time are observed in the late-plateau phase spectra of SN 2015ba, which suggests a possible role of circumstellar interaction at these phases. Both hydrodynamical and analytical modelling suggest a massive progenitor of SN 2015ba with a pre-explosion mass of 24-26 M$_\odot$. However, the nebular spectra of SN 2015ba exhibit insignificant levels of oxygen, which is otherwise expected from a massive progenitor. This might be suggestive of the non-monotonical link between O-core masses and the zero-age main-sequence mass of pre-supernova stars and/or uncertainties in the mixing scenario in the ejecta of supernovae.