ANALYSIS OF THE EARLY-TIME OPTICAL SPECTRA OF SN 2011fe IN M101

Parrent, J. T.; Howell, D. A.; Friesen, B.; Thomas, R. C.; Fesen, R. A.; Milisavljevic, D.; Bianco, F. B.; Dilday, B.; Nugent, P.; Baron, E.; Arcavi, I.; Ben-Ami, S.; Bersier, D.; Bildsten, L.; Bloom, J.; Cao, Y.; Cenko, S. B.; Filippenko, A. V.; Gal-Yam, A.; Kasliwal, M. M.; Konidaris, N.; Kulkarni, S. R.; Law, N. M.; Levitan, D.; Maguire, K.; Mazzali, P. A.; Ofek, E. O.; Pan, Y.; Polishook, D.; Poznanski, D.; Quimby, R. M.; Silverman, J. M.; Sternberg, A.; Sullivan, M.; Walker, E. S.; Xu, Dong; Buton, C.; Pereira, R.
2012
ASTROPHYSICAL JOURNAL LETTERS
DOI
10.1088/2041-8205/752/2/L26
The nearby Type Ia supernova (SN Ia) SN 2011fe in M101 (cz = 241 km s(-1)) provides a unique opportunity to study the early evolution of a "normal" SN Ia, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000 km s(-1). This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNe Ia. The observed evolution of the highlyDoppler-shifted OI lambda 7774 absorption features detected within 5 days post-explosion indicates the presence of OI with expansion velocities from 11,500 to 21,000 km s(-1). The fact that some OI is present above C II suggests that SN 2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta.