Cosmological Constraints from Measurements of Type Ia Supernovae discovered during the first 1.5 years of the Pan-STARRS1 Survey

We present griz light curves of 146 spectroscopically confirmed Type Ia Supernovae ($0.03 < z <0.65$) discovered during the first 1.5 years of the Pan-STARRS1 Medium Deep Survey. The Pan-STARRS1 natural photometric system is determined by a combination of on-site measurements of the instrument response function and observations of spectrophotometric standard stars. We find that the systematic uncertainties in the photometric system are currently 1.2% without accounting for the uncertainty in the HST Calspec definition of the AB system. A Hubble diagram is constructed with a subset of 113 out of 146 SNe Ia that pass our light curve quality cuts. The cosmological fit to 310 SNe Ia (113 PS1 SNe Ia + 222 light curves from 197 low-z SNe Ia), using only SNe and assuming a constant dark energy equation of state and flatness, yields $w=-1.120^{+0.360}_{-0.206}textrm{(Stat)} ^{+0.269}_{-0.291}textrm{(Sys)}$. When combined with BAO+CMB(Planck)+$H_0$, the analysis yields $Omega_{rm M}=0.280^{+0.013}_{-0.012}$ and $w=-1.166^{+0.072}_{-0.069}$ including all identified systematics (see also Scolnic et al. 2014). The value of $w$ is inconsistent with the cosmological constant value of $-1$ at the 2.3$sigma$ level. Tension endures after removing either the BAO or the $H_0$ constraint, though it is strongest when including the $H_0$ constraint. If we include WMAP9 CMB constraints instead of those from Planck, we find $w=-1.124^{+0.083}_{-0.065}$, which diminishes the discord to $<2sigma$. We cannot conclude whether the tension with flat $Lambda$CDM is a feature of dark energy, new physics, or a combination of chance and systematic errors. The full Pan-STARRS1 supernova sample with $sim!!$3 times as many SNe should provide more conclusive results.

Systematic Uncertainties Associated with the Cosmological Analysis of the First Pan-STARRS1 Type Ia Supernova Sample

We probe the systematic uncertainties from 113 Type Ia supernovae (SNIa) 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. (2013) 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 0.037pm0.031 mag for host galaxies with high and low masses. Assuming flatness in our analysis of only SNe measurements, we find $w = {-1.120^{+0.360}_{-0.206}textrm{(Stat)} ^{+0.269}_{-0.291}textrm{(Sys)}}$. With additional constraints from BAO, CMB(Planck) and H0 measurements, we find $w = -1.166^{+0.072}_{-0.069}$ and $Omega_M=0.280^{+0.013}_{-0.012}$ (statistical and systematic errors added in quadrature). Significance of the inconsistency with $w=-1$ depends on whether we use Planck or WMAP measurements of the CMB: $w_{textrm{BAO+H0+SN+WMAP}}=-1.124^{+0.083}_{-0.065}$.