OPTICAL OBSERVATIONS OF THE TYPE IA SUPERNOVA SN 2011fe IN M101 FOR NEARLY 500 DAYS
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ABSTRACTWe present well-sampled optical observations of the bright Type Ia supernova (SN Ia) SN 2011fe in M101. Our data, starting from 16 days before maximum light and extending to 463 days after maximum, provide an unprecedented time series of spectra and photometry for a normal SNIa. Fitting the early-time rising light curve, we find that the luminosity evolution of SN 2011fe follows a tn law, with the index n being close to 2.0 in the VRI bands but slightly larger in the U and B bands. Combining the published ultraviolet (UV) and near-infrared (NIR) photometry, we derive the contribution of UV/NIR emission relative to the optical. SN 2011fe is found to have stronger UV emission and reaches its UV peak a few days earlier than other SNeIa with similar m15(B), suggestive of less trapping of high-energy photons in the ejecta. Moreover, the U-band light curve shows a notably faster decline at late phases (t100300 days), which also suggests that the ejecta may be relatively transparent to UV photons. These results favor the notion that SN 2011fe might have a progenitor system with relatively lower metallicity. On the other hand, the early-phase spectra exhibit prominent high-velocity features (HVFs) of O i7773 and the Ca iiNIR triplet, but only barely detectable in Si ii6355. This difference can be caused byeitheran ionization/temperature effect or an abundance enhancement scenario for the formation of HVFs; it suggests that the photospheric temperature of SN 2011fe is intrinsically low, perhaps owing to incomplete burning during the explosion of the white dwarf.
