SN 2023xwi: Forbidden line emission in the peak spectrum of a Ca-strong transient

TL;DR

This paper presents detailed observations of the Ca-rich supernova SN2023xwi, highlighting its unique early appearance of forbidden calcium emission in the peak spectrum, challenging existing models and suggesting a novel progenitor environment.

Contribution

It reports the earliest detection of forbidden [Ca II] emission in a Ca-rich supernova's peak spectrum and proposes a new progenitor scenario involving a He-nova polluted environment.

Findings

Forbidden [Ca II] emission observed in peak spectrum earlier than expected.

Spectral velocity evolution inconsistent with conventional progenitors.

Proposed progenitor embedded in a He-nova polluted environment.

Abstract

We present an extensive optical photometric and spectroscopic investigation into the calcium-rich supernova (SN) - SN2023xwi. Observations from a variety of ground-based telescopes follow the SN from 8 days pre-peak brightness to 87 days post-peak, covering both early-time (photospheric) and late-time (nebular) phases of the supernova. Objects of this class are characterised by nebular spectra that are dominated by [Ca II] $\lambda \lambda$ 7291, 7324 emission. SN 2023xwi displays a unique peculiarity in that its forbidden [Ca II] feature is visible in its peak photospheric spectrum - far earlier than expected in current models. This is one of the strongest and earliest detections of this feature in Ca-rich SNe in photospheric-phase spectra. We investigate the velocity evolution of this spectral feature and show that it cannot be easily explained by conventional progenitor systems. From our observations, we propose a SN progenitor embedded in an environment polluted by a recurrent He-nova AM CVn system.