# Signatures of Circumstellar Interaction in the Type IIL Supernova ASASSN-15oz

## TL;DR

This study investigates circumstellar interaction in the Type IIL supernova ASASSN-15oz, revealing evidence of significant pre-explosion mass loss through multi-wavelength observations and modeling, challenging traditional views on supernova classifications.

## Contribution

It provides the first detailed multi-wavelength analysis of a Type IIL supernova, demonstrating the role of circumstellar material and mass-loss history in its explosion characteristics.

## Key findings

- Evidence of intense mass loss 1800 R_sun from progenitor.
- Detection of radio emission indicating mass-loss rates of 10^{-6} to 10^{-7} M_sun/yr.
- Upper limit on mass-loss rate outside extreme period is <10^{-4} M_sun/yr.

## Abstract

Hydrogen-rich, core-collapse supernovae are typically divided into four classes: IIP, IIL, IIn, and IIb. In general, interaction with circumstellar material is only considered for Type IIn supernovae. However, recent hydrodynamic modeling of IIP and IIL supernovae requires circumstellar material to reproduce their early light curves. In this scenario, IIL supernovae experience large amounts of mass loss before exploding. We test this hypothesis on ASASSN-15oz, a Type IIL supernova. With extensive follow-up in the X- ray, UV, optical, IR, and radio we present our search for signs of interaction, and the mass-loss history indicated by their detection. We find evidence of short-lived intense mass-loss just prior to explosion from light curve modeling, amounting in 1.5 M$_{\odot}$ of material within 1800 R$_{\odot}$ of the progenitor. We also detect the supernova in the radio, indicating mass-loss rates of $10^{-6}-10^{-7}$ M$_{\odot}$ yr$^{-1}$ prior to the extreme mass-loss period. Our failure to detect the supernova in the X-ray and the lack of narrow emission lines in the UV, optical, and NIR do not contradict this picture and place an upper limit on the mass-loss rate outside the extreme period of $<10^{-4}$ M$_{\odot}$ yr$^{-1}$. This paper highlights the importance gathering comprehensive data on more Type II supernovae to enable detailed modeling of the progenitor and supernova which can elucidate their mass-loss histories and envelope structures and thus inform stellar evolution models.