Hubble Space Telescope spectra of the type Ia supernova SN2011fe: a tail of low-density, high-velocity material with Z<Zsolar

• Published in: arXiv.org 2014-01
• Main Authors: Mazzali, Paolo, Sullivan, Mark, Hachinger, Stephan, Ellis, Richard, Nugent, Peter E, Howell, D Andrew, Gal-Yam, Avishay, Maguire, Kate, Cooke, Jeff, Rollin, Thomas, Nomoto, Ken, Walker, Emma
• Format: Article
• Language: English
• Subjects: Computer simulation; Density distribution; Detonation; Ejecta; Explosions; Hubble Space Telescope; Light curve; Metallicity; Model matching; Model testing; Photometry; Radiative transfer; Space telescopes; Spectra; Stratification; White dwarf stars
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1305.2356

Hubble Space Telescope spectroscopic observations of the nearby type Ia supernova (SN Ia) SN2011fe, 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 SN2011fe the best-studied local SN Ia to date. SN2011fe 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 (Maguire et al. 2012). The near-UV to optical spectra of SN2011fe 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. SN2011fe 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). The derived Fe abundance in the outermost layer is consistent with the metallicity at the SN explosion site in M101 (~0.5 Zsolar). The spectroscopic rise time (~19 days) is significantly longer than that measured from the early optical light curve, implying a 'dark phase' of ~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.