ROUGH DRAFT authorea.com/85775

# Pre-SN Mass-loss

Abstract

Our goal is to reconstruct pre-SN mass-loss history using radio variability observations and constrain the dominant mass-loss mechanism during the last few hundred years of massive star evolution. We will draw from existing observations to re-design the strategy for future observing campaigns.

# Introduction

Observations are painting a complex picture of massive stars at the end of their lives. Contrary to expectations, massive stars have been found to experience major eruptions in the years preceding their explosion as supernovae (SNe). This sequence of eruptions was not predicted on theoretical grounds and is not explained by our current understanding of the physical mechanisms that drive the mass loss in evolved massive stars (Smith 2014).

In this respect, two key observational findings are relevant: (i) The direct detection of luminous precursors in the month before the major explosion of the H-rich SN2009ip associated with the ejection of $$\sim0.1\,\rm{M_{\odot}}$$ of material (Margutti et al., 2014). (ii) Evidence for significant modulations in the radio light-curves of hydrogen-stripped SNe (e.g. SNe Ib/c; Wellons et al., 2012). This latter finding indicates that a complex environment, sculpted and enriched by a significantly non-steady mass loss of the progenitor system in the years before the explosion, surrounds some Type Ib/c SNe.

The two findings above suggest that massive stars might lose their hydrogen envelopes through eruptive mass ejections (instead of steady winds, as it has been assumed so far) on time scales of months to decades before the core-collapse (i.e. much shorter than previously thought). To test this idea here we propose a focused collaborative effort to probe the life of massive stars in the last centuries before death. Our goal is to reconstruct the density profile and mass-loss history of core-collapse SNe (i) using the entire sample of existing radio observations, (ii) treating the dynamics of the SN shock interaction with the complex medium in a self-consistent way and (iii) by finally connecting our findings to the physics that regulates the time-variable mass loss in massive stars.

\label{fig} The density profile around a nearby Ib SN as probed by recent radio observations (black solid line) [i] violates the expectations from the standard theory of line driven winds (orange line), [ii] requires a different physical explanation and [iii] motivates a deep and rigorous search for density enhancements in the environment of core-collapse SNe. The overarching goal of the project is to provide a state-of-the art view of our current understanding of mass-loss from massive stars. Using existing data we will design the strategy of future follow up in the non-thermal part of the spectrum based on the parts of the parameter space that has not been sampled so far.

To help constrain mass-loss theory, we first need to understand the mass-loss history of massive stars. In particular, we need to know the mass-loss rate ($$\dot{M}$$) and velocity as a function of time before explosion.
The mass loss rates during the last few hundred years of evolution of some core collapse supernova progenitors seem to violate the maximum values allowed by line-driven winds ($$\dot{M} \sim 10^{-4}$$M$$_\odot$$yr$$^{-1}$$, (Smith 2006), see also Fig. \ref{fig}).