On the nature of slowly rising interaction-powered supernovae

TL;DR

This paper explains that long rise times in interaction-powered supernovae are due to flat-density circumstellar matter, revealing insights into massive star mass loss through supernova observations.

Contribution

It demonstrates that flat CSM density profiles naturally produce long supernova rise times, offering a new perspective on supernova light curve modeling.

Findings

Long rise times are caused by flat CSM density profiles.

The rise time depends on the reverse shock propagation, not photon diffusion.

Long rise supernovae probe extensive non-steady mass loss in massive stars.

Abstract

Some interaction-powered supernovae have long rise times of more than 100 days. We show that such long rise times are naturally expected if circumstellar matters (CSM) have a flat density structure (s <~ 1.5, where rho_CSM ~ r^{-s}). In such cases, bolometric luminosities from the CSM interaction keep increasing as long as the CSM interacts with the outer layers of the SN ejecta. Thus, the rise time is determined by the dynamical timescale in which the reverse shock propagates the outer layers of the SN ejecta, not by the timescales in which photons diffuse in the CSM as often considered. Interaction-powered supernovae with very long rise times can be an important probe of extensive non-steady mass loss in massive stars.