### Abstract

We present griz_{P1} light curves of 146 spectroscopically confirmed Type Ia supernovae (SNe Ia; 0.03 < z < 0.65) discovered during the first 1.5 yr 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 Hubble Space Telescope 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 supernovae (SNe) and assuming a constant dark energy equation of state and flatness, yields w = -1.120^{+0.360}_{-0.206}(Stat)^{+0.269}_{0.291}(Sys). When combined with BAO+CMB(Planck)+H_{0}, the analysis yields Ω_{M} = 0.280^{+0.013}_{0.012} and w = -1.166^{+0.072}_{-0.069} including all identified systematics. The value of w is inconsistent with the cosmological constant value of -1 at the 2.3σ level. Tension endures after removing either the baryon acoustic oscillation (BAO) or the H_{0} constraint, though it is strongest when including the H_{0} constraint. If we include WMAP9 cosmic microwave background (CMB) constraints instead of those from Planck, we find w = -1.124^{+0.083}_{-0.065}, which diminishes the discord to <2σ. We cannot conclude whether the tension with flat ΛCDM is a feature of dark energy, new physics, or a combination of chance and systematic errors. The full Pan-STARRS1 SN sample with ∼three times as many SNe should provide more conclusive results.

Original language | English |
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Article number | 44 |

Journal | Astrophysical Journal |

Volume | 795 |

Issue number | 1 |

DOIs | |

Publication status | Published - 01 Nov 2014 |

### Keywords

- cosmological parameters
- cosmology: observations
- dark energy
- supernovae: general

### ASJC Scopus subject areas

- Space and Planetary Science
- Astronomy and Astrophysics

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## Cite this

*Astrophysical Journal*,

*795*(1), [44]. https://doi.org/10.1088/0004-637X/795/1/44