Author(s): Fakhouri, HK; Boone, K; Aldering, G; Antilogus, P; Aragon, C; Bailey, S; Baltay, C; Barbary, K; Baugh, D; Bongard, S; Buton, C; Chen, J; Childress, M; Chotard, N; Copin, Y; Fagrelius, P; Feindt, U; Fleury, M; Fouchez, D; Gangler, E; Hayden, B; Kim, AG; Kowalski, M; Leget, PF; Lombardo, S; Nordin, J; Pain, R; Pecontal, E; Pereira, R; Perlmutter, S; Rabinowitz, D; Ren, J; Rigault, M; Rubin, D; Runge, K; Saunders, C; Scalzo, R; Smadja, G; Sofiatti, C; Strovink, M; Suzuki, N; Tao, C; Thomas, RC; Weaver, BA | Abstract: We introduce a method for identifying "twin" Type Ia supernovae (SNe Ia) and using them to improve distance measurements. This novel approach to SN Ia standardization is madeossible by spectrophotometric time series observations from the Nearby Supernova Factory (SNfactory). We begin with a well-measured set of SNe, findairs whose spectra match well across the entire optical window, and then test whether this leads to a smaller dispersion in their absolute brightnesses. This analysis is completed in a blinded fashion, ensuring that decisions made in implementing the method do not inadvertently bias the result. We find thatairs of SNe with more closely matched spectra indeed have reduced brightness dispersion. We are able to standardize this initial set of SNfactory SNe to 0.083 0.012 mag, implying a dispersion of 0.072 0.010 mag in the absence ofeculiar velocities. We estimate that with larger numbers of comparison SNe, e.g., using the final SNfactory spectrophotometric data set as a reference, this method will be capable of standardizing high-redshift SNe to within 0.06-0.07 mag. These results imply that at least 3/4 of the variance in Hubble residuals in current SN cosmology analyses is due toreviously unaccounted-for astrophysical differences among the SNe.

/pdf/improving-cosmological-distance-measurements-using-twin-type-3mpyi2t80k.pdf

Improving Cosmological Distance Measurements Using Twin Type Ia Supernovae

We introduce a method for identifying "twin" Type Ia supernovae, and using them to improve distance measurements. This novel approach to Type Ia supernova standardization is made possible by spectrophotometric time series observations from the Nearby Supernova Factory (SNfactory). We begin with a well-measured set of supernovae, find pairs whose spectra match well across the entire optical window, and then test whether this leads to a smaller dispersion in their absolute brightnesses. This analysis is completed in a blinded fashion, ensuring that decisions made in implementing the method do not inadvertently bias the result. We find that pairs of supernovae with more closely matched spectra indeed have reduced brightness dispersion. We are able to standardize this initial set of SNfactory supernovae to 0.083 +/- 0.012 magnitudes, implying a dispersion of 0.072 +/- 0.010 magnitudes in the absence of peculiar velocities. We estimate that with larger numbers of comparison SNe, e.g, using the final SNfactory spectrophotometric dataset as a reference, this method will be capable of standardizing high-redshift supernovae to within 0.06-0.07 magnitudes. These results imply that at least 3/4 of the variance in Hubble residuals in current supernova cosmology analyses is due to previously unaccounted-for astrophysical differences among the supernovae

/pdf/improving-cosmological-distance-measurements-using-twin-type-91csm3e5e6.pdf

Over the last 20 years, supernovae have become a key tool to constrain the expansion history of the Universe through the construction of Hubble diagrams, using luminosity distances to supernovae belonging to the 'Ia' subtype. This technique was key for the discovery that the expansion of the Universe is now accelerating. We review the principle and difficulties of the measurements, the classification and diversity of supernovae, and the physics of explosion. We discuss the systematic uncertainties affecting the cosmological conclusions with some emphasis on photometric calibration. We describe the major supernova cosmology surveys, the presented analyses and their conclusions, together with the present status of the field. We conclude on the expectations for the near future.

https://iopscience.iop.org/article/10.1088/0034-4885/75/11/116901/pdf

The expansion of the universe observed with supernovae

L'etalonnage photometrique des imageurs grand champ est a ce jour la principale limitation pour plusieurs mesures de cosmologie, parmi lesquelles celle des parametres cosmologiques a l'aide des supernovae de type Ia Afin d'obtenir l'exactitude de l'ordre de 01% necessaire pour les releves futurs, les collaborations actives dans ce domaine explorent la possibilite de nouvelles techniques de calibration a l'aide d'instruments dedies comme alternative a celle traditionnelle a l'aide d'etoiles standard spectrophotometriques Le groupe du LPNHE a concu SnDICE, un systeme d'illumination innovant et tres stable qui a ete installe dans la dome du telescope Canada-France-Hawaii pour calibrer l'imageur MegaCam et en suivre les performances Le but est de demontrer la faisabilite d'une calibration instrumentale absolue exacte a 01% ou mieux Dans la premiere partie de la these, un bref apercu du modele standard de la cosmologie et des principales sondes etudiees pour en contraindre les parametres est suivi par la description de MegaCam et SnDICE La seconde partie s'attache a presenter la construction d'un modele optique de MegaCam et d'une modelisation geometrique permettant de connaitre les attitudes de MegaCam et SnDICE dans le dome Ces deux modeles ont ete implementes dans un logiciel traceur de rayons, cree a l'aide des librairies ROOT, de facon a simuler l'eclairement du plan focal Cette simulation permet de distin- guer l'illumination directe des contributions dues aux reflexions issues des surfaces du correcteur grand champ Enfin, est presentee l'application de ces outils pour la premiere analyse des poses de calibration SnDICE : la determination de la bande passante rM de MegaCam

Calibration photométrique de l'imageur MegaCam. Analyse des données SnDICE.

Observational cosmology employing optical surveys often require precise flux calibration. In this context we present SNIFS Calibration Apparatus (SCALA), a flux calibration system developed for the SuperNova Integral Field Spectrograph (SNIFS), operating at the University of Hawaii 2.2 m telescope. SCALA consists of a hexagonal array of 18 small parabolic mirrors distributed over the face of, and feeding parallel light to, the telescope entrance pupil. The mirrors are illuminated by integrating spheres and a wavelength-tunable (from UV to IR) light source, generating light beams with opening angles of 1 degree. These nearly parallel beams are flat and flux-calibrated at a subpercent level, enabling us to calibrate our "telescope + SNIFS system" at the required precision.

A flux calibration device for the SuperNova Integral Field Spectrograph (SNIFS)

We present the first results of the SuperNova Direct Illumination Calibration Experiment (SNDICE), installed
in January 2008 at the Canada France Hawaii Telescope SNDICE is designed for the absolute calibration of
the instrumental response of a telescope in general, and for the control of systematic errors in the SuperNova
Legacy Survey (SNLS) on Megacam in particular Since photometric calibration will a critical ingredient for
the cosmological results of future experiments involving instruments with large focal planes (like SNAP, LSST
and DUNE), SNDICE functions also as a real-size demonstrator for such a system of instrumental calibration
SNDICE includes a calibrated source of 24 LEDs, chosen for their stability, spectral coverage, and their power,
sufficient for a flux of at least 100 electron/s/pixel on the camera It includes also Cooled Large Area Photodiode
modules (CLAPs), which give a redundant measurement of the flux near the camera focal plane Before installing
SNDICE on CFHT, we completed a full calibration of both subsystems, including a spectral relative calibration
and a 3D mapping of the beam emitted by each LED At CFHT, SNDICE can be operated both to obtain a
complete one-shot absolute calibration of telescope transmission in all wavelengths for all filters with several
incident angles, and to monitor variations on different time scales

SNDICE: a direct illumination calibration experiment at CFHT

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SNDICE: a direct illumination calibration experiment at CFHT