2014ApJ...795...45S

We probe the systematic uncertainties from the 113 Type Ia supernovae (SN Ia) in the Pan-STARRS1 (PS1) sample along with 197 SN Ia from a combination of low-redshift surveys. The companion paper by Rest et al. describes the photometric measurements and cosmological inferences from the PS1 sample. The largest systematic uncertainty stems from the photometric calibration of the PS1 and low-z samples. We increase the sample of observed Calspec standards from 7 to 10 used to define the PS1 calibration system. The PS1 and SDSS-II calibration systems are compared and discrepancies up to ∼0.02 mag are recovered. We find uncertainties in the proper way to treat intrinsic colors and reddening produce differences in the recovered value of w up to 3%. We estimate masses of host galaxies of PS1 supernovae and detect an insignificant difference in distance residuals of the full sample of 0.037±0.031 mag for host galaxies with high and low masses. Assuming flatness and including systematic uncertainties in our analysis of only SNe measurements, we find ω = -1.120_–0.206^+0.360(Stat)_–0.291^+0.296(Sys). With additional constraints from Baryon acoustic oscillation, cosmic microwave background (CMB) (Planck) and H₀measurements, we find ω = -1.166_0.069^+0.072 and Ω = 0.280_–0.012^+0.013 (statistical and systematic errors added in quadrature). The significance of the inconsistency with ω = -1 depends on whether we use Planck or Wilkinson Microwave Anisotropy Probe measurements of the CMB: ω_{BAO+H0+SN+WMAP}=-1.124_–0.065^+0.083.