We present optical light curves, redshifts, and classifications for 365 spectroscopically confirmed Type Ia supernovae (SNe Ia) discovered by the Pan-STARRS1 (PS1) Medium Deep Survey. We detail improvements to the PS1 SN photometry, astrometry and calibration that reduce the systematic uncertainties in the PS1 SN Ia distances. We combine the subset of 279 PS1 SN Ia (0.03 < z < 0.68) with useful distance estimates of SN Ia from SDSS, SNLS, various low-z and HST samples to form the largest combined sample of SN Ia consisting of a total of 1048 SN Ia ranging from 0.01 < z < 2.3, which we call the 'Pantheon Sample'. When combining Planck 2015 CMB measurements with the Pantheon SN sample, we find Ω m = 0.307±0.012 and w = −1.026±0.041 for the wCDM model. When the SN and CMB constraints are combined with constraints from BAO and local H 0 measurements, the analysis yields the most precise measurement of dark energy to date: w 0 = −1.007 ± 0.089 and w a = −0.222 ± 0.407 for the w 0 w a CDM model. Tension with a cosmological constant previously seen in an analysis of PS1 and low-z SNe has diminished after an increase of 2× in the statistics of the PS1 sample, improved calibration and photometry, and stricter light-curve quality cuts. We find the systematic uncertainties in our measurements of dark energy are almost as large as the statistical uncertainties, primarily due to limitations of modeling the low-redshift sample. This must be addressed for future progress in using SN Ia to measure dark energy.

The DESI Legacy Imaging Surveys (http://legacysurvey.org/) are a combination of three public projects (the Dark Energy Camera Legacy Survey, the Beijing-Arizona Sky Survey, and the Mayall z-band Legacy Survey) that will jointly image ≈14,000 deg 2 of the extragalactic sky visible from the northern hemisphere in three optical bands (g, r, and z) using telescopes at the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory. The combined survey footprint is split into two contiguous areas by the Galactic plane. The optical imaging is conducted using a unique strategy of dynamically adjusting the exposure times and pointing selection during observing that results in a survey of nearly uniform depth. In addition to calibrated images, the project is delivering a catalog, constructed by using a probabilistic inference-based approach to estimate source shapes and brightnesses. The catalog includes photometry from the grz optical bands and from four mid-infrared bands (at 3.4, 4.6, 12, and 22 μm) observed by the Wide-field Infrared Survey Explorer satellite during its full operational lifetime. The project plans two public data releases each year. All the software used to generate the catalogs is also released with the data. This paper provides an overview of the Legacy Surveys project.

We present constraints on the dark energy equation-of-state parameter, w ¼ P/( c 2 ), using 60 SNe Ia from the ESSENCE supernova survey. We derive a set of constraints on the nature of the dark energy assuming a flat universe. By including constraints on ( M , w) from baryon acoustic oscillations, we obtain a value for a static equation-of-state parameter w ¼ À1:05 þ0:13 À0:12 (stat 1 ) AE 0:13 (sys) and M ¼ 0:274 þ0:033 À0:020 (stat 1 ) with a bestfit 2 /dof of 0.96. These results are consistent with those reported by the Supernova Legacy Survey from the first year of a similar program measuring supernova distances and redshifts. We evaluate sources of systematic error that afflict supernova observations and present Monte Carlo simulations that explore these effects. Currently, the largest systematic with the potential to affect our measurements is the treatment of extinction due to dust in the supernova host galaxies. Combining our set of ESSENCE SNe Ia with the first-results Supernova Legacy Survey SNe Ia, we obtain a joint constraint of w ¼ À1:07 þ0:09 À0:09 (stat 1 ) AE 0:13 (sys), M ¼ 0:267 þ0:028 À0:018 (stat 1 ) with a best-fit 2 /dof of 0.91. The current global SN Ia data alone rule out empty ( M ¼ 0), matter-only M ¼ 0:3, and M ¼ 1 universes at >4.5 . The current SN Ia data are fully consistent with a cosmological constant.

The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant galaxies 1 . Previous candidate flares 2-6 have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two 'relativistic' candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet 7-10 . Here we report the discovery of a luminous ultraviolet-optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decline of its light curve follows the predicted mass accretion rate, and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about 2 million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core.When the pericenter of a star's orbit (R p ) passes within the tidal disruption radius of a massive black hole, R T ≈ R ⋆ (M BH /M ⋆ ) 1/3 , tidal forces overcome the binding energy of the 1 star, which breaks up with roughly half of the stellar debris remaining bound to the black hole and the rest being ejected at high velocity 1 . For black holes above a critical mass,, the star becomes trapped within the event horizon of the black hole before being disrupted. The mass accretion rate (Ṁ ) in a tidal disruption event (TDE) can be calculated directly from the orbital return-times of the bound debris 1,11,12 . For the simplest case of a star of uniform density this yields,Ṁ = 2 3 ( f M⋆ t min )( t t min ) −5/3 , where f is the fraction of the star accreted and t min is the orbital period of the most tightly bound debris and, therefore, the time delay between the time of disruption and the start of the flare, which scales asThe radiative output of the accreted debris is less certain, and depends on the ratio of the accretion rate to the Eddington rate 13 . Table 2). No source is detected in a deep coadd of all the TDS epochs in 2009, with a 3σ upper limit of > 25.6 mag implying a peak amplitude of variability in the NUV of > 6.4 mag. See the Supplementary Information for details on the PS1 and GALEX photometry. PS1-10jh is coincident with the centre of a galaxy within the 3σ positional uncertainty (0.036 arcsec; Supplementary Information) with rest-frame u, g, r, i, and z photometry from SDSS 16 and K photometry from UKIDSS 17 fitted with a galaxy template 18 with M stars = (3.6 ± 0.2) × 10 9 M ⊙ and M r = −18.7 mag, where M stars is the galaxy stellar mass and M r is the absolute r-band...