Rest-Frame R-band Light Curve of a z ∼ 1.3 Supernova Obtained with Keck Laser Adaptive Optics

We present Keck diffraction-limited H-band photometry of a z ∼ 1.3 Type Ia supernova (SN) candidate, first identified in a Hubble Space Telescope search for SNe in massive high-redshift galaxy clusters. The adaptive optics (AO) data were obtained with the Laser Guide Star facility during four observing runs from 2005 September to November. In the analysis of data from the observing run nearest to maximum SN brightness, the SN was found to have a magnitude H = 23.9 ± 0.14 (Vega). We present the H-band (approximately rest-frame R) light curve and provide a detailed analysis of the AO photometric uncertainties. By constraining the aperture correction with a nearby (4″ separation) star we achieve 0.14 mag photometric precision, despite the spatially varying AO point-spread function.