Spitzer Mid-Infrared Detections of Neutron Star Merger GW170817 Suggests Synthesis of the Heaviest Elements

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We report our Spitzer Space Telescope observations and detections of the binary neutron star merger GW170817.

• At 4.5um, GW170817 is detected at 21.9 mag AB at +43 days and 23.9 mag AB at +74 days after merger.
• At 3.6um, GW170817 is not detected to a limit of 23.2 mag AB at +43 days and 23.1 mag AB at +74 days.
• Our detections constitute the latest and reddest constraints on the kilonova/macronova emission and composition of heavy elements.