The See Change survey was designed to make $z>1$ cosmological
measurements by efficiently discovering high-redshift Type Ia supernovae
(SNe Ia) and improving cluster mass measurements through weak lensing.
This survey observed twelve galaxy clusters with the Hubble Space
Telescope spanning the redshift range $z=1.13$ to $1.75$, discovering 57
likely transients and 27 likely SNe Ia at $z\sim 0.8-2.3$. As in similar
previous surveys (Dawson et al. 2009), this proved to be a highly
efficient use of HST for SN observations; the See Change survey
additionally tested the feasibility of maintaining, or further
increasing, the efficiency at yet higher redshifts, where we have less
detailed information on the expected cluster masses and star-formation
rates. We find that the resulting number of SNe Ia per orbit is a factor
of $\sim 8$ higher than for a field search, and 45% of our orbits
contained an active SN Ia within 22 rest-frame days of peak, with one of
the clusters by itself yielding 6 of the SNe Ia. We present the survey
design, pipeline, and SN discoveries. Novel features include fully
blinded SN searches, the first random forest candidate classifier for
undersampled IR data (with a 50% detection threshold within 0.05
magnitudes of human searchers), real-time forward-modeling photometry of
candidates, and semi-automated photometric classifications and follow-up
forecasts. We also describe the spectroscopic follow-up, instrumental in
measuring host-galaxy redshifts. The cosmology analysis of our sample
will be presented in a companion paper.
This is an author-created, un-copyedited version of an article accepted for publication/published in The Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi:10.3847/1538-4357/abed4d