Spectroscopy of the Type Ia supernova 2011fe past 1000 days

Abstract

In this letter we present an optical spectrum of SN 2011fe taken 1034 d after the explosion, several hundred days later than any other spectrum of a Type Ia supernova (disregarding light-echo spectra and local-group remnants). The spectrum is still dominated by broad emission features, with no trace of a light echo or interaction of the supernova ejecta with surrounding interstellar material. Comparing this extremely late spectrum to an earlier one taken 331 d after the explosion, we find that the most prominent feature at 331 d - [Fe III] emission around 4700 A - has entirely faded away, suggesting a significant change in the ionisation state. Instead, [Fe II] lines are probably responsible for most of the emission at 1034 d. An emission feature at 6300-6400 A has newly developed at 1034 d, which we tentatively identify with Fe I λ6359, [Fe I] λλ6231, 6394 or [O I] λλ6300, 6364. Interestingly, the features in the 1034-d spectrum seem to be collectively redshifted, a phenomenon that we currently have no convincing explanation for. We discuss the implications of our findings for explosion models, but conclude that sophisticated spectral modelling is required for any firm statement.

6 pages, 3 figures, MNRAS Letters accepted

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• Extremely late photometry of SN~2011fe
• Confirmation of Hostless Type Ia Supernovae Using Hubble Space Telescope Imaging
• A Rapid Ionization Change in the Nebular-Phase Spectra of the Type Ia SN 2011fe
• A year-long plateau in the late-time near-infrared light curves of Type Ia supernovae
• The Whisper of a Whimper of a Bang: 2400 Days of the Type Ia SN 2011fe Reveals the Decay of ${}^{55}$Fe
• The intermediate nebular phase of SN 2014J: onset of clumping as the source of recombination
• Near-infrared and Optical Nebular-phase Spectra of Type Ia Supernovae SN 2013aa and SN 2017cbv in NGC 5643
• Searching for late-time interaction signatures in Type Ia supernovae from the Zwicky Transient Facility
• The HST Non-Detection of SN Ia 2011fe 11.5yr After Explosion Further Restricts Single-Degenerate Progenitor Systems
• Including a Luminous Central Remnant in Radiative Transfer Simulations for Type Iax Supernovae
• Building spectral templates and reconstructing parameters for core collapse supernovae with CASTOR