Late-Time Infrared Cooling in Magnetar-Driven Supernovae

TL;DR

This study investigates late-time infrared cooling in magnetar-driven supernovae, showing that infrared emission, especially from Ne II, dominates cooling after several years and can be detected with JWST out to redshift 0.1.

Contribution

It provides detailed models of infrared cooling processes in magnetar-driven supernovae, highlighting the transition from optical to infrared dominance over time and the observability with JWST.

Findings

Infrared cooling dominates after 6 years post-explosion.

[Ne II] 12.8μm is the strongest coolant at late times.

Infrared emission can be detected with JWST out to z~0.1.

Abstract

A central magnetar engine is commonly invoked to explain energetic supernovae, which should have multiple signals in multiwavelength emission. Photoionization from the pulsar wind nebula (PWN) can create distinct spectroscopic signals in the nebular phase. Recent models suggest infrared emission, particularly from Ne II, can be prominent at late times. This work examines the cooling power of optical and infrared transitions to determine which lines contribute strongly to cooling and on what timescale. The models show infrared cooling becomes strong at $\sim$ 3 years post-explosion and dominates by 6 years, with [Ne II] 12.8$\mu$m being the strongest coolant. The fraction of total cooling in the infrared increases sharply once the PWN luminosity decreases below 10$^{40}$ erg s$^{-1}$, and this fraction also increases with increasing ejecta mass and decreasing average PWN photon energy. However, the emission from [Ne II] 12.8$\mu$m increases with increasing PWN luminosity and increasing ejecta mass. Cooling at 1 year is dominated by optical O and S lines, with infrared Ar, Ni, and Ne lines becoming strong at 3 years. Optical cooling is almost negligible at 6 years, with the supernova cooling almost entirely through mid- and far-infrared transitions. JWST spectroscopy with MIRI should be able to detect these lines out to $z \sim 0.1$. Supernovae with higher magnetic fields transition to infrared cooling on earlier timescales, while infrared-dominated supernovae should have strong emission from neutral atoms and emit strongly in radio at sub-decade timescales.