Hubble Space Telescope spectroscopic observations of the nearby type Ia supernova ( SN Ia ) SN 2011fe , taken on 10 epochs from - 13.1 to + 40.8 days relative to B -band maximum light , and spanning the far-ultraviolet ( UV ) to the near-infrared ( IR ) are presented .
This spectroscopic coverage makes SN 2011fe the best-studied local SN Ia to date .
SN 2011fe is a typical moderately-luminous SN Ia with no evidence for dust extinction .
Its near-UV spectral properties are representative of a larger sample of local events ( 47 ) .
The near-UV to optical spectra of SN 2011fe are modelled with a Monte Carlo radiative transfer code using the technique of ‘ abundance tomography ’ , constraining the density structure and the abundance stratification in the SN ejecta .
SN 2011fe was a relatively weak explosion , with moderate Fe-group yields .
The density structures of the classical model W7 and of a delayed detonation model were tested .
Both have shortcomings .
An ad-hoc density distribution was developed which yields improved fits and is characterised by a high-velocity tail , which is absent in W7 .
However , this tail contains less mass than delayed detonation models .
This improved model has a lower energy than one-dimensional explosion models matching typical SNe Ia ( e.g .
W7 , WDD1 , 36 ) .
The derived Fe abundance in the outermost layer is consistent with the metallicity at the SN explosion site in M101 ( \sim 0.5 Z _ { \odot } ) .
The spectroscopic rise time ( \sim 19 days ) is significantly longer than that measured from the early optical light curve , implying a ‘ dark phase ’ of \sim 1 day .
A longer rise time has significant implications when deducing the properties of the white dwarf and binary system from the early photometric behaviour .