We present the first cosmological parameter constraints using measurements of type Ia supernovae (SNe Ia) from the Dark Energy Survey Supernova Program (DES-SN). The analysis uses a subsample of 207 spectroscopically confirmed SNe Ia from the first three years of DES-SN, combined with a low-redshift sample of 122 SNe from the literature. Our “DES-SN3YR” result from these 329 SNe Ia is based on a series of companion analyses and improvements covering SN Ia discovery, spectroscopic selection, photometry, calibration, distance bias corrections, and evaluation of systematic uncertainties. For a flat ΛCDM model we find a matter density . For a flat wCDM model, and combining our SN Ia constraints with those from the cosmic microwave background (CMB), we find a dark energy equation of state , and . For a flat w 0 w a CDM model, and combining probes from SN Ia, CMB and baryon acoustic oscillations, we find and . These results are in agreement with a cosmological constant and with previous constraints using SNe Ia (Pantheon, JLA).

We present the analysis underpinning the measurement of cosmological parameters from 207 spectroscopically classified SNe Ia from the first 3 years of the Dark Energy Survey Supernova Program (DES-SN), spanning a redshift range of 0.017<z<0.849. We combine the DES-SN sample with an external sample of 122 low-redshift (z < 0.1) SNeIa, resulting in a "DES-SN3YR" sample of 329 SNeIa. Our cosmological analyses are blinded: after combining our DES-SN3YR distances with constraints from the Cosmic Microwave Background, our uncertainties in the measurement of the dark energy equation-of-state parameter, w, are 0.042(stat) and 0.059(stat+syst) at 68% confidence. We provide a detailed systematic uncertainty budget, which has nearly equal contributions from photometric calibration, astrophysical bias corrections, and instrumental bias corrections. We also include several new sources of systematic uncertainty. While our sample is less than one-third the size of the Pantheon sample, our constraints on w are only larger by 1.4×, showing the impact of the DES-SNIa light-curve quality. We find that the traditional stretch and color standardization parameters of the DES-SNeIa are in agreement with earlier SNIa samples such as Pan-STARRS1 and the Supernova Legacy Survey. However, we find smaller intrinsic scatter about the Hubble diagram (0.077 mag). Interestingly, we find no evidence for a Hubble residual step (0.007 ± 0.018 mag) as a function of host-galaxy mass for the DES subset, in 2.4σ tension with previous measurements. We also present novel validation methods of our sample using simulated SNeIa inserted in DECam images and using large catalog-level simulations to test for biases in our analysis pipelines.

The Wide Field InfraRed Survey Telescope (WFIRST) was the highest ranked large space-based mission of the 2010 New Worlds, New Horizons decadal survey. It is now a NASA mission in formulation with a planned launch in the mid-2020's. A primary mission objective is to precisely constrain the nature of dark energy through multiple probes, including Type Ia supernovae. Here, we present the first realistic simulations of the WFIRST SN survey based on current hardware specifications and using open-source tools. We simulate SN light curves and spectra as viewed by the WFIRST wide-field channel (WFC) imager and integral field channel (IFC) spectrometer, respectively. We examine 11 survey strategies with different time allocations between the WFC and IFC, two of which are based upon the strategy described by the WFIRST Science Definition Team, which measures SN distances exclusively from IFC data. We apply selection criteria and analysis methods based on recent SN cosmological analyses. We propagate statistical and, crucially, systematic uncertainties to predict the dark energy task force figure of merit (DETF FoM) for each strategy. The increase in FoM values with SN search area is limited by the overhead times for each exposure, and the dependence of the FoM on the maximum redshift is limited by the parameterisation of dark energy. For IFC-focused strategies the largest individual systematic uncertainty is the wavelength-dependent calibration uncertainty, whereas for WFC-focused strategies, it is the intrinsic scatter uncertainty. We consider the impact of potential reductions to each systematic uncertainty before launch, resulting in a range of FoMs for each strategy. We find that the best IFC-focused and WFCexclusive strategies have comparable FoM values. Even without improvements to other cosmological probes, the WFIRST SN survey has the potential to increase the FoM by more than an order of magnitude from the current values. Although the survey strategies presented here have not been fully optimised, these initial investigations are an important step in the development of the final hardware design and implementation of the WFIRST mission.

We test a cosmological model which the only component is a pressureless fluid with a constant bulk viscosity as an explanation for the present accelerated expansion of the universe. We classify all the possible scenarios for the universe predicted by the model according to their past, present and future evolution and we test its viability performing a Bayesian statistical analysis using the SCP "Union" data set (307 SNe Ia), imposing the second law of thermodynamics on the dimensionless constant bulk viscous coefficientζ and comparing the predicted age of the universe by the model with the constraints coming from the oldest globular clusters.The best estimated values found forζ and the Hubble constant H 0 are:ζ = 1.922 ± 0.089 and H 0 = 69.62 ± 0.59 (km/s)Mpc −1 with a χ 2 min = 314 (χ 2 d.o.f = 1.031). The age of the universe is found to be 14.95 ± 0.42 Gyr. We see that the estimated value of H 0 as well as of χ 2 d.o.f are very similar to those obtained from ΛCDM model using the same SNe Ia data set. The estimated age of the universe is in agreement with the constraints coming from the oldest globular clusters. Moreover, the estimated value ofζ is positive in agreement with the second law of thermodynamics (SLT).On the other hand, we perform different forms of marginalization over the parameter H 0 in order to study the sensibility of the results to the way how H 0 is marginalized. We found that it is almost negligible the dependence between the best estimated values of the free parameters of this model and the way how H 0 is marginalized in the present work.Therefore, this simple model might be a viable candidate to explain the present acceleration in the expansion of the universe.PACS numbers: 95.36.+x, 98.80.Es

We describe the simulated data sample for the "Photometric LSST Astronomical Time Series Classification Challenge" (PLAsTiCC), a publicly available challenge to classify transient and variable events that will be observed by the Large Synoptic Survey Telescope (LSST), a new facility expected to start in the early 2020s. The challenge was hosted by Kaggle, ran from 2018 September 28 to 2018 December 17, and included 1,094 teams competing for prizes. Here we provide details of the 18 transient and variable source models, which were not revealed until after the challenge, and release the model libraries at https://doi.org/10.5281/zenodo.2612896. We describe the LSST Operations Simulator used to predict realistic observing conditions, and we describe the publicly available SNANA simulation code used to transform the models into observed fluxes and uncertainties in the LSST passbands (ugrizy). Although PLAsTiCC has finished, the publicly available models and simulation tools are being used within the astronomy community to further improve classification, and to study contamination in photometrically identified samples of type Ia supernova used to measure properties of dark energy. Our simulation framework will continue serving as a platform to improve the PLAsTiCC models, and to develop new models.