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SN 2017eaw, the tenth supernova observed in NGC 6946, was a normal Type II-Psupernova with an estimated 11 - 13 Msun supergiant progenitor. Here we presentnebular phase spectra of SN 2017eaw at +545 and +900 days post-max, extendingapproximately 50 - 400 days past the epochs of previously published spectra.While the +545 day spectra is similar to spectra taken between days +400 and+493, the +900 day spectrum shows dramatic changes both in spectral featuresand emission line profiles. The Halpha emission is flat-topped and box-likewith sharp blue and red profile velocities of ~ -8000 and +7500 km/s. Theselate-time spectral changes indicate strong circumstellar interaction with amass-loss shell, expelled ~ 1700 years before explosion. SN 2017eaw's +900 dayspectrum is similar to those seen for SN 2004et and SN 2013ej observed 2 - 3years after explosion. We discuss the importance of late-time monitoring ofbright SNe II-P and the nature of pre-supernova mass-loss events for SN II-Pevolution.

Detection of Late-Time Circumstellar Interaction of SN 2017eaw in NGC 6946