EVLA Observations Constrain the Environment and Progenitor System of
  Type Ia Supernova 2011fe
  We report unique EVLA observations of SN 2011fe representing the most
sensitive radio study of a Type Ia supernova to date. Our data place direct
constraints on the density of the surrounding medium at radii ~10^15-10^16 cm,
implying an upper limit on the mass loss rate from the progenitor system of
Mdot <~ 6 x 10^-10 Msol/yr (assuming a wind speed of 100 km/s), or expansion
into a uniform medium with density n_CSM <~ 6 cm^-3. Drawing from the observed
properties of non-conservative mass transfer among accreting white dwarfs, we
use these limits on the density of the immediate environs to exclude a phase
space of possible progenitors systems for SN 2011fe. We rule out a symbiotic
progenitor system and also a system characterized by high accretion rate onto
the white dwarf that is expected to give rise to optically-thick accretion
winds. Assuming that a small fraction, 1%, of the mass accreted is lost from
the progenitor system, we also eliminate much of the potential progenitor
parameter space for white dwarfs hosting recurrent novae or undergoing stable
nuclear burning. Therefore, we rule out the most popular single degenerate
progenitor models for SN 2011fe, leaving a limited phase space inhabited by
some double degenerate systems and exotic progenitor scenarios.
