Uniform Recalibration of Common Spectrophotometry Standard Stars onto
  the CALSPEC System using the SuperNova Integral Field Spectrograph
  We calibrate spectrophotometric optical spectra of 32 stars commonly used as
standard stars, referenced to 14 stars already on the HST-based CALSPEC flux
system. Observations of CALSPEC and non-CALSPEC stars were obtained with the
SuperNova Integral Field Spectrograph over the wavelength range 3300 A to 9400
A as calibration for the Nearby Supernova Factory cosmology experiment. In
total, this analysis used 4289 standard-star spectra taken on photometric
nights. As a modern cosmology analysis, all pre-submission methodological
decisions were made with the flux scale and external comparison results
blinded. The large number of spectra per star allows us to treat the
wavelength-by-wavelength calibration for all nights simultaneously with a
Bayesian hierarchical model, thereby enabling a consistent treatment of the
Type Ia supernova cosmology analysis and the calibration on which it critically
relies. We determine the typical per-observation repeatability (median 14 mmag
for exposures >~ 5 s), the Maunakea atmospheric transmission distribution
(median dispersion of 7 mmag with uncertainty 1 mmag), and the scatter internal
to our CALSPEC reference stars (median of 8 mmag). We also check our standards
against literature filter photometry, finding generally good agreement over the
full 12-magnitude range. Overall, the mean of our system is calibrated to the
mean of CALSPEC at the level of ~ 3 mmag. With our large number of
observations, careful crosschecks, and 14 reference stars, our results are the
best calibration yet achieved with an integral-field spectrograph, and among
the best calibrated surveys.
