Abstract
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 0.037\pm0.031 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: $w_{\textrm{BAO+H0+SN+WMAP}}=-1.124^{+0.083}_{-0.065}$.
Highlights
One of the main goals of the Pan-STARRS1 (PS1) Medium Deep survey is to detect and monitor thousands of Type Ia supernovae (SN Ia) in order to measure the equation-of-state parameter of dark energy, w = P /ρc2
We remove any observations of Calspec standards where there is greater than a 0.03 mag difference between the aperture and pointspread function (PSF) photometry, as we found this adequately removes any saturated observations
We find that the change in w when the PS1 calibration system is chosen to be in agreement with Sloan Digital Sky Survey (SDSS) is Δw = +0.018 with constraints only from SN measurements, and Δw = −0.006 when including cosmic microwave background (CMB), Baryon acoustic oscillation (BAO), and H0 constraints
Summary
Since the initial discovery of cosmic acceleration (Riess et al 1998; Perlmutter et al 1999), there have been many supernova surveys utilizing multiple passbands and dense time-sampling at both low-z (e.g., CSP,CfA1-4, LOSS, SNFactory18) and at intermediate and higher-z (e.g., Sloan Digital Sky Survey (SDSS), ESSENCE, SNLS19). Most of the systematic uncertainties in the analysis of these samples fall into a small handful of categories: calibration, selection effects, correlated flows, extinction corrections and light curve modeling. The companion paper by R14 analyzes the photometry of the PS1 light curves, presents the light curve fit parameters and derives constraints on w from a combined data set of PS1 SNe and low-z SNe (hereafter PS1+lz).
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