Very late photometry of SN 2011fe

TL;DR

This study presents extremely late-time photometry of SN 2011fe, revealing that its optical light curve continues to be powered by decay positrons, challenging some theoretical expectations of rapid dimming due to energy loss mechanisms.

Contribution

First to provide photometric data of SN 2011fe at over 900 days, demonstrating continued positron thermalization contrary to some models predicting rapid fading.

Findings

Optical light curve consistent with full positron thermalization.

No evidence of infrared catastrophe or significant positron escape.

Supernova remains luminous at 930 days, longer than expected.

Abstract

The Type Ia supernova SN 2011fe is one of the closest supernovae of the past decades. Due to its proximity and low dust extinction, this object provides a very rare opportunity to study the extremely late time evolution ($>900$ days) of thermonuclear supernovae. In this Letter, we present our photometric data of SN 2011fe taken at an unprecedented late epoch of $\approx 930$ days with GMOS-N mounted on the Gemini North telescope ($g=23.43 \pm 0.28$, $r=24.14 \pm 0.14$, $i=23.91 \pm 0.18$, and $z=23.90 \pm 0.17$) to study the energy production and retention in the ejecta of SN 2011fe. Together with previous measurements by other groups, our result suggests that the optical supernova light curve can still be explained by the full thermalization of the decay positrons of Co56. This is in spite of theoretical predicted effects (e.g. infrared catastrophe, positron escape, and dust) that advocate a substantial energy redistribution and/or loss via various processes that result in a more rapid dimming at these very late epochs.