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An examination of late-time, optical spectra of type Ia supernovae revealedsurprisingly narrow absorption features which only become visible a few monthsafter maximum light. These features, most clearly seen in the late-time spectraof the bright, recent type Ia supernovae ASASSN-14lp and SN 2017bzc, appear asnarrow absorptions at ~4840 A, ~5000 A, and as a sharp inflection at ~4760 A onthe red side of the prominent late-time 4700 A feature. A survey of on-linearchival data revealed similar features present in the spectra of ten othernormal and 91T-like SNe Ia, including SN 2011fe. Unlike blue spectral featureswhich exhibit progressive red-ward shifts, these narrow absorptions remain atthe same wavelength from epoch to epoch for an individual SN, but can appear atslightly different wavelengths for each object. These features are alsotransient, appearing and then fading in one to three months. After ruling outinstrumental, data reduction, and atmospheric affects, we discuss possibleexplanations including progenitor mass-loss material, interaction with materialfrom previous novae events, and absorption by large discrete clumps ofhigh-velocity Fe-rich ejecta.

Narrow Transient Absorptions in Late-Time Optical Spectra of Type Ia Supernovae: Evidence for Large Clumps of Iron-Rich Ejecta?