CfA4: Light Curves for 94 Type Ia Supernovae
  We present multi-band optical photometry of 94 spectroscopically-confirmed
Type Ia supernovae (SN Ia) in the redshift range 0.0055 to 0.073, obtained
between 2006 and 2011. There are a total of 5522 light curve points. We show
that our natural system SN photometry has a precision of roughly 0.03 mag or
better in BVr'i', 0.06 mag in u', and 0.07 mag in U for points brighter than
17.5 mag and estimate that it has a systematic uncertainty of 0.014, 0.010,
0.012, 0.014, 0.046, and 0.073 mag in BVr'i'u'U, respectively. Comparisons of
our standard system photometry with published SN Ia light curves and comparison
stars reveal mean agreement across samples in the range of ~0.00-0.03 mag. We
discuss the recent measurements of our telescope-plus-detector throughput by
direct monochromatic illumination by Cramer et al (in prep.). This technique
measures the whole optical path through the telescope, auxiliary optics,
filters, and detector under the same conditions used to make SN measurements.
Extremely well-characterized natural-system passbands (both in wavelength and
over time) are crucial for the next generation of SN Ia photometry to reach the
0.01 mag accuracy level. The current sample of low-z SN Ia is now sufficiently
large to remove most of the statistical sampling error from the dark energy
error budget. But pursuing the dark-energy systematic errors by determining
highly-accurate detector passbands, combining optical and near-infrared (NIR)
photometry and spectra, using the nearby sample to illuminate the population
properties of SN Ia, and measuring the local departures from the Hubble flow
will benefit from larger, carefully measured nearby samples.
