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Abstract The first few hours of a supernova (SN) contain significant information about the progenitor system. The most modern wide-field surveys that scan the sky repeatedly every few days can discover all kinds of transients in those early epochs.At such times, some progenitor footprints may be visible, elucidating critical explosion parameters and helping to distinguish between leading explosion models.A dedicated spectroscopic classification programme using the optical spectrograph OSIRIS mounted on the Gran Telescopio de Canarias was set up to try to obtain observations of supernovae (SNe) at those early epochs.With the time awarded, we obtained spectra of 10 SN candidates, which we present here. Half of them were thermonuclear SNe, while the other half were core-collapse SNe. Most (70%) were observed within the first six days of the estimated explosion, with two being captured within the first 48 hours. We present a characterization of the spectra, together with other public ancillary photometry from theZwicky Transient Facility (ZTF) and the Asteroid Terrestrial-impact Last Alert System (ATLAS).This project shows the need for an accompanying rapid-response spectroscopic programme for existing and future deep photometric wide-field surveys located at the right longitude to be able to trigger observations in a few hours after the discovery of the SN candidate.Both the future La Silla Southern Supernova Survey (LS4) and the Legacy Survey of Space and Time (LSST), both located in Chile, will be providing discovery and follow-up of most of the transients in the southern hemisphere. This paper demonstrates that with a rapid spectroscopic programme and stringent triggering criteria, obtaining a sample of SN with spectra within a day of the explosion is possible. 

Abstract Here we present 1701 light curves of 1550 unique, spectroscopically confirmed Type Ia supernovae (SNe Ia) that will be used to infer cosmological parameters as part of the Pantheon+ SN analysis and the Supernovae and H 0 for the Equation of State of dark energy distance-ladder analysis. This effort is one part of a series of works that perform an extensive review of redshifts, peculiar velocities, photometric calibration, and intrinsic-scatter models of SNe Ia. The total number of light curves, which are compiled across 18 different surveys, is a significant increase from the first Pantheon analysis (1048 SNe), particularly at low redshift ( z ). Furthermore, unlike in the Pantheon analysis, we include light curves for SNe with z < 0.01 such that SN systematic covariance can be included in a joint measurement of the Hubble constant ( H 0 ) and the dark energy equation-of-state parameter ( w ). We use the large sample to compare properties of 151 SNe Ia observed by multiple surveys and 12 pairs/triplets of “SN siblings”—SNe found in the same host galaxy. Distance measurements, application of bias corrections, and inference of cosmological parameters are discussed in the companion paper by Brout et al., and the determination of H 0 is discussed by Riess et al. These analyses will measure w with ∼3% precision and H 0 with ∼1 km s −1 Mpc −1 precision. 

Abstract We present constraints on cosmological parameters from the Pantheon+ analysis of 1701 light curves of 1550 distinct Type Ia supernovae (SNe Ia) ranging in redshift from z = 0.001 to 2.26. This work features an increased sample size from the addition of multiple cross-calibrated photometric systems of SNe covering an increased redshift span, and improved treatments of systematic uncertainties in comparison to the original Pantheon analysis, which together result in a factor of 2 improvement in cosmological constraining power. For a flat ΛCDM model, we find Ω M = 0.334 ± 0.018 from SNe Ia alone. For a flat w 0 CDM model, we measure w 0 = −0.90 ± 0.14 from SNe Ia alone, H 0 = 73.5 ± 1.1 km s −1 Mpc −1 when including the Cepheid host distances and covariance (SH0ES), and w 0 = − 0.978 − 0.031 + 0.024 when combining the SN likelihood with Planck constraints from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO); both w 0 values are consistent with a cosmological constant. We also present the most precise measurements to date on the evolution of dark energy in a flat w 0 w a CDM universe, and measure w a = − 0.1 − 2.0 + 0.9 from Pantheon+ SNe Ia alone, H 0 = 73.3 ± 1.1 km s −1 Mpc −1 when including SH0ES Cepheid distances, and w a = − 0.65 − 0.32 + 0.28 when combining Pantheon+ SNe Ia with CMB and BAO data. Finally, we find that systematic uncertainties in the use of SNe Ia along the distance ladder comprise less than one-third of the total uncertainty in the measurement of H 0 and cannot explain the present “Hubble tension” between local measurements and early universe predictions from the cosmological model.