# The Nearby Type Ibn Supernova 2015G: Signatures of Asymmetry and Progenitor Constraints

## TL;DR

This paper reports extensive multi-wavelength observations of the nearby Type Ibn supernova 2015G, revealing asymmetry, hydrogen-free circumstellar material, and constraints on the progenitor's mass-loss history.

## Contribution

It provides detailed observational evidence of asymmetry and circumstellar environment in SN 2015G, offering new insights into the progenitor's mass-loss and explosion characteristics.

## Key findings

- SN 2015G was asymmetric with redshifted nebular lines.
- The circumstellar medium was hydrogen-free and moving at ~1000 km/s.
- Progenitor luminosity constraints suggest recent mass loss.

## Abstract

We present the results of an extensive observational campaign on the nearby Type Ibn SN 2015G, including data from radio through ultraviolet wavelengths. SN 2015G was asymmetric, showing late-time nebular lines redshifted by ~1000 km/s. It shared many features with the prototypical SN In 2006jc, including extremely strong He I emssion lines and a late-time blue pseudocontinuum. The young SN 2015G showed narrow P-Cygni profiles of He I, but never in its evolution did it show any signature of hydrogen - arguing for a dense, ionized, and hydrogen-free circumstellar medium moving outward with a velocity of ~1000 km/s and created by relatively recent mass loss from the progenitor star. Ultraviolet through infrared observations show that the fading SN 2015G (which was probably discovered some 20 days post-peak) had a spectral energy distribution that was well described by a simple, single-component blackbody. Archival HST images provide upper limits on the luminosity of SN 2015G's progenitor, while nondetections of any luminous radio afterglow and optical nondetections of outbursts over the past two decades provide constraints upon its mass-loss history.