Optical Cross Correlation Filters: An Economical Approach for
  Identifying SNe Ia and Estimating their Redshifts
  Large photometric surveys of transient phenomena, such as Pan-STARRS and
LSST, will locate thousands to millions of type Ia supernova candidates per
year, a rate prohibitive for acquiring spectroscopy to determine each
candidate's type and redshift. In response, we have developed an economical
approach to identifying SNe Ia and their redshifts using an uncommon type of
optical filter which has multiple, discontinuous passbands on a single
substrate. Observation of a supernova through a specially designed pair of
these `cross-correlation filters' measures the approximate amplitude and phase
of the cross-correlation between the spectrum and a SN Ia template, a quantity
typically used to determine the redshift and type of a high-redshift SN Ia.
Simulating the use of these filters, we obtain a sample of SNe Ia which is ~98%
pure with individual redshifts measured to 0.01 precision. The advantages of
this approach over standard broadband photometric methods are that it is
insensitive to reddening, independent of the color data used for subsequent
distance determinations which reduces selection or interpretation bias, and
because it makes use of the spectral features its reliability is greater. A
great advantage over long-slit spectroscopy comes from increased throughput,
enhanced multiplexing and reduced set-up time resulting in a net gain in speed
of up to ~30 times. This approach is also insensitive to host galaxy
contamination. Prototype filters were built and successfully used on Magellan
with LDSS-3 to characterize three SNLS candidates. We discuss how these filters
can provide critical information for the upcoming photometric supernova
surveys.
