Final Spitzer IRAC Observations of the Rise and Fall of SN 1987A

TL;DR

This paper reports on final Spitzer IRAC observations of SN 1987A, showing the equatorial ring's infrared emission declining and evolving in morphology, with implications for dust and material destruction, and highlights a serendipitous discovery of a variable Be star.

Contribution

It provides detailed infrared imaging and analysis of SN 1987A's equatorial ring evolution, revealing brightness asymmetries and morphological changes, and discusses future JWST observations.

Findings

Infrared emission from the ring is dominated by the west side.

The IR morphological changes mirror those in X-ray and optical.

The ring's IR light curves resemble optical curves more than X-ray ones.

Abstract

Spitzer's final Infrared Array Camera (IRAC) observations of SN 1987A show the 3.6 and 4.5 $\mu$m emission from the equatorial ring (ER) continues a period of steady decline. Deconvolution of the images reveals that the emission is dominated by the ring, not the ejecta, and is brightest on the west side. Decomposition of the marginally resolved emission also confirms this, and shows that the west side of the ER has been brightening relative to the other portions of the ER. The infrared (IR) morphological changes resemble those seen in both the soft X-ray emission and the optical emission. The integrated ER light curves at 3.6 and 4.5 $\mu$m are more similar to the optical light curves than the soft X-ray light curve, though differences would be expected if dust is responsible for this emission and its destruction is rapid. Future observations with the James Webb Space Telescope will continue to monitor the ER evolution, and will reveal the true spectrum and nature of the material responsible for the broadband emission at 3.6 and 4.5 $\mu$m. The present observations also serendipitously reveal a nearby variable source, subsequently identified as a Be star, that has gone through a multi-year outburst during the course of these observations.