TYPE Ia SUPERNOVA LIGHT CURVE INFERENCE: HIERARCHICAL MODELS IN THE OPTICAL AND NEAR-INFRARED

Abstract

We have constructed a comprehensive statistical model for Type Ia supernova (SN Ia) light curves spanning optical through near infrared (NIR) data. A hierarchical framework coherently models multiple random and uncertain effects, including intrinsic supernova light curve covariances, dust extinction and reddening, and distances. An improved BayeSN MCMC code computes probabilistic inferences for the hierarchical model by sampling the global probability density of parameters describing individual supernovae and the population. We have applied this hierarchical model to optical and NIR data of 127 SN Ia from PAIRITEL, CfA3, CSP, and the literature. We find an apparent population correlation between the host galaxy extinction A V and the the ratio of total-to-selective dust absorption R V . For SN with low dust extinction, A V 0.4, we find R V ≈ 2.5 − 2.9, while at high extinctions, A V 1, low values of R V < 2 are favored. The NIR luminosities are excellent standard candles and are less sensitive to dust extinction. They exhibit low correlation with optical peak luminosities, and thus provide independent information on distances. The combination of NIR and optical data constrains the dust extinction and improves the predictive precision of individual SN Ia distances by about 60%. Using cross-validation, we estimate an rms distance modulus prediction error of 0.11 mag for SN with optical and NIR data versus 0.15 mag for SN with optical data alone. Continued study of SN Ia in the NIR is important for improving their utility as precise and accurate cosmological distance indicators.

Observational probes of cosmic acceleration

“…For the bulk of the population, the prevailing picture is that the progenitor explosions produce varying amounts of Ni 56 , whose radioactivity powers the optical luminosity, and that the correlation of peak luminosity with light curve shape arises from radiative transfer effects (Hoeflich et al 1996;Kasen and Woosley 2007). Recent studies suggest that SN Ia are truly standard candles in the near-IR, with peak luminosities at rest-frame H-band (1.6 µm) that have only ∼ 0.1 magnitude rms dispersion independent of light curve shape, and with little sensitivity to uncertain reddening laws (Mandel et al 2009(Mandel et al , 2011Barone-Nugent et al 2012). This small dispersion in near-IR peak luminosities relative to optical is consistent with theoretical expectations from radiative transfer models (Kasen, 2006).…”

“…An optimal approach should therefore allow for both effects. Bayesian fitting methods (e.g., Mandel et al 2009Mandel et al , 2011 can in principle incorporate a wide variety of parameterized relationships with explicit priors, including dependences on redshift or host galaxy parameters, which are then marginalized over in cosmological fits. At the level of precision of current SN samples, the differences in fitting methods do matter (e.g., Kessler et al 2009), so this remains an area of active research.…”

BAHAMAS: NEW ANALYSIS OF TYPE Ia SUPERNOVAE REVEALS INCONSISTENCIES WITH STANDARD COSMOLOGY

“…By contrast, the Multi-color Lightcurve Shape (Riess et al 1996;Jha et al 2007) approach simultaneously infers the Phillips corrections and the cosmological parameters of interest, while explicitly modeling the dust absorption and reddening in the host galaxy. Recently, a fully Bayesian, hierarchical model approach to LC fitting has emerged (Mandel et al 2009(Mandel et al , 2011, but this so-called BAYESN algorithm has not yet been applied for inferring cosmological parameters.…”

Testing supernovae Ia distance measurement methods with SN 2011fe

“…This is the major source of the relatively small, but still existing random and systematic errors that limit the precision and accuracy of the derived distances (see e.g. Mandel et al 2011, for further discussion and references). SN 2011fe (aka PTF11kly, Nugent et al 2011) is an excellent object in this respect, because this bright (m peak ∼ 10 mag), nearby (D ∼ 6.5 Mpc) SN Ia was discovered hours after explosion Bloom et al 2012) and suffered from very little interstellar reddening (A V ∼ 0.04 mag, Nugent et al 2011;Patat et al 2012).…”