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

Abstract

Spitzer's final Infrared Array Camera observations of SN 1987A show the 3.6 and 4.5 μm 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 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 μm 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 μm. The present observations also serendipitously reveal a nearby variable source, subsequently identified as a Be star, that has gone through a multiyear outburst during the course of these observations.