We study the optical light curve (LC) relations of Type Ia supernovae (SNe Ia) for their use in cosmology using high-quality photometry published by the Carnegie Supernova Project (CSP-I). We revisit the classical luminosity decline rate (Delta m(15)) relation and the Lira relation, as well as investigate the time evolution of the (B V) color and B(B - V), which serves as the basis of the color-stretch relation and Color-MAgnitude Intercept Calibrations (CMAGIC). Our analysis is based on explosion and radiation transport simulations for spherically symmetric delayed-detonation models (DDT) producing normal-bright and subluminous SNe. Ia. Empirical LC relations can be understood as having the same physical underpinnings, i.e., opacities, ionization balances in the photosphere, and radioactive energy deposition changing with time from below to above the photosphere. Some three to four weeks past maximum, the photosphere recedes to Ni-56-rich layers of similar density structure, leading to a similar color evolution. An important secondary parameter is the central density rho(c) of the WD because at higher densities, more electron-capture elements are produced at the expense of Ni-56 production. This results in a.m15 spread of 0.1 mag in normal-bright and 0.7 mag in subluminous SNe. Ia and approximate to 0.2 mag in the Lira relation. We show why color-magnitude diagrams emphasize the transition between physical regimes and enable the construction of templates that depend mostly on Delta(m15) with little dispersion in both the CSP-I sample and our DDT models. This allows intrinsic SN. Ia variations to be separated from the interstellar reddening characterized by E (B - V) and R-B. Invoking different scenarios causes a wide spread in empirical relations, which may suggest one dominant scenario.

We present final natural-system optical (ugriBV) and near-infrared (YJH) photometry of 134 supernovae (SNe) with probable white dwarf progenitors that were observed in 2004-2009 as part of the first stage of the Carnegie Supernova Project (CSP-I). The sample consists of 123 Type. Ia SNe, 5 Type. Iax SNe, 2 super-Chandrasekhar SN candidates, 2 Type. Ia SNe interacting with circumstellar matter, and 2 SN. 2006bt-like events. The redshifts of the objects range from z = 0.0037 to 0.0835; the median redshift is 0.0241. For 120 (90%) of these SNe, near-infrared photometry was obtained. Average optical extinction coefficients and color terms are derived and demonstrated to be stable during the five CSP-I observing campaigns. Measurements of the CSP-I near-infrared bandpasses are also described, and near-infrared color terms are estimated through synthetic photometry of stellar atmosphere models. Optical and near-infrared magnitudes of local sequences of tertiary standard stars for each supernova are given, and a new calibration of Y-band magnitudes of the Persson et al. standards in the CSP-I natural system is presented.

We present detailed ultraviolet, optical, and near-infrared light curves of the Type Ia supernova (SN) 2012fr, which exploded in the Fornax cluster member NGC 1365. These precise high-cadence light curves provide a dense coverage of the flux evolution from -12 to +140 days with respect to the epoch of B-band maximum (t(Bmax)). Supplementary imaging at the earliest epochs reveals an initial slow and nearly linear rise in luminosity with a duration of similar to 2.5 days, followed by a faster rising phase that is well reproduced by an explosion model with a moderate amount of Ni-56 mixing in the ejecta. From our analysis of the light curves, we conclude that: (i) the explosion occurred <22 hr before the first detection of the supernova, (ii) the rise time to peak bolometric (lambda > 1800 angstrom) luminosity was 16.5 +/- 0.6 days, (iii) the supernova suffered little or no host-galaxy dust reddening, (iv) the peak luminosity in both the optical and near-infrared was consistent with the bright end of normal Type Ia diversity, and (v) 0.60 +/- 0.15 M-circle dot of Ni-56 was synthesized in the explosion. Despite its normal luminosity, SN 2012fr displayed unusually prevalent high-velocity Ca II and Si II absorption features, and a nearly constant photospheric velocity of the Si II lambda 6355 line at similar to 12,000 km s(-1) that began similar to 5 days before t(Bmax) We also highlight some of the other peculiarities in the early phase photometry and the spectral evolution. SN 2012fr also adds to a growing number of Type Ia supernovae that are hosted by galaxies with direct Cepheid distance measurements.

Radiative transfer models of two transitional type Ia supernova (SNe Ia) have been produced using the abundance stratification technique. These two objects - designated SN 2007on and SN 2011iv - both exploded in the same galaxy, NGC 1404, which allows for a direct comparison. SN 2007on synthesised 0.25 M-circle dot of Ni-56 and was less luminous than SN 2011iv, which produced 0.31 M-circle dot of Ni-56. SN 2007on had a lower central density (rho(c)) and higher explosion energy (E-kin similar to 1.3 +/- 0.3x10(51)erg) than SN 2011iv, and it produced less nuclear statistical equilibrium (NSE) elements (0.06 M-circle dot). Whereas, SN 2011iv had a larger rho(c), which increased the electron capture rate in the lowest velocity regions, and produced 0.35 M-circle dot of stable NSE elements. SN 2011iv had an explosion energy of similar to E-kin similar to 0.9 +/- 0.2x10(51)erg. Both objects had an ejecta mass consistent with the Chandrasekhar mass (Ch-mass), and their observational properties are well described by predictions from delayed-detonation explosion models. Within this framework, comparison to the sub-luminous SN 1986G indicates SN 2011iv and SN 1986G have different transition densities (rho(tr)) but similar rho(c). Whereas, SN 1986G and SN 2007on had a similar rho(tr) but different rho(c). Finally, we examine the colour-stretch parameter sBV vs. L-max relation and determine that the bulk of SNe Ia (including the sub-luminous ones) are consistent with Ch-mass delayed-detonation explosions, where the main parameter driving the diversity is rho(tr). We also find rho(c) to be driving the second order scatter observed at the faint end of the luminosity-width relationship.

We examine the early phase intrinsic (B - V)(0) color evolution of a dozen SNe Ia discovered within three days of the inferred time of first light (t(first)) and have (B - V)(0) color information beginning within five days of t(first). The sample indicates there are two distinct early populations. The first is a population exhibiting blue colors that slowly evolve, and the second population exhibits red colors and evolves more rapidly. We find that the early blue events are all 1991T/1999aa-like with more luminous, slower declining light curves than those exhibiting early red colors. Placing the first sample on the Branch diagram (i.e., ratio of Si II lambda lambda 5972, 6355 pseudo-Equivalent widths) indicates that all blue objects are of the Branch shallow silicon (SS) spectral type, while all early red events except for the 2000cx-like SN 2012fr are of the Branch Core Normal (CN) or CooL (CL) type. A number of potential processes contributing to the early emission are explored, and we find that, in general, the viewing-angle dependance inherent in the companion collision model is inconsistent with all of the SS objects with early-time observations being blue and exhibiting an excess. We caution that great care must be taken when interpreting early phase light curves as there may be a variety of physical processes that are possibly at play and significant theoretical work remains to be done.

We present an analysis of the final data release of the Carnegie Supernova Project I, focusing on the absolute calibration of the luminosity-decline rate relation for Type Ia supernovae (SNe Ia) using new intrinsic color relations with respect to the color-stretch parameter, s(BV), enabling improved dust extinction corrections. We investigate to what degree the so-called fast-declining SNe. Ia can be used to determine accurate extragalactic distances. We estimate the intrinsic scatter in the luminosity-decline rate relation and find it ranges from +/- 0.13 mag to +/- 0.18 mag with no obvious dependence on wavelength. Using the Cepheid variable star data from the SH0ES project, the SN. Ia distance scale is calibrated and the Hubble constant is estimated using our optical and near-infrared sample, and these results are compared to those determined exclusively from a near-infrared subsample. The systematic effect of the supernova's host galaxy mass is investigated as a function of wavelength and is found to decrease toward redder wavelengths, suggesting this effect may be due to dust properties of the host. Using estimates of the dust extinction derived from optical and near-infrared wavelengths and applying these to the H band, we derive a Hubble constant H-0 73.2+/-2.3 km s(-1) Mpc(-1) whereas using a simple B - V color correction applied to the B band yields H-0 72.7+/-2.1 km s(-1) Mpc(-1) Photometry of two calibrating SNe. Ia from the CSP-II sample, SN. 2012ht and SN. 2015F, is presented and used to improve the calibration of the SN. Ia distance ladder.

We aim to improve upon contemporary methods to estimate host-galaxy reddening of stripped-envelope (SE) supernovae (SNe). To this end the Carnegie Supernova Project (CSP-I) SE SN photometry data release, consisting of nearly three dozen objects, is used to identify a minimally reddened sub-sample for each traditionally defined spectroscopic sub-type (i.e., SNe IIb, SNe Ib, SNe Ic). Inspection of the optical and near-infrared (NIR) colors and color evolution of the minimally reddened sub-samples reveals a high degree of homogeneity, particularly between 0 d to +20 d relative to B-band maximum. This motivated the construction of intrinsic color-curve templates, which when compared to the colors of reddened SE SNe, yields an entire suite of optical and NIR color excess measurements. Comparison of optical/optical vs. optical/NIR color excess measurements indicates the majority of the CSP-I SE SNe suffer relatively low amounts of reddening (i.e., E(B - V)(host) < 0.20 mag) and we find evidence for different R-host(V) values among di ff erent SE SN. Fitting the color excess measurements of the seven most reddened (i. e., E(B - V)(host) > 0.20 mag) objects with the Fitzpatrick (1999, PASP, 111, 63) reddening law model provides robust estimates of the host visual-extinction A(host)(V) and R-host(V). In the case of the SE SNe with relatively low amounts of reddening, a preferred value of R-host(V) is adopted for each sub-type, resulting in estimates of A(V)(host) through Fitzpatrick (1999) reddening law model fits to the observed color excess measurements. Our analysis suggests SE SNe reside in galaxies characterized by a range of dust properties. We also find evidence that SNe Ic are more likely to occur in regions characterized by larger A(V)(host) values compared to SNe IIb/Ib and they also tend to suffer more extinction. The later finding is consistent with work in the literature suggesting SNe Ic tend to occur in regions of on-going star formation.

Stripped-envelope (SE) supernovae (SNe) include H-poor (Type IIb), H-free (Type Ib), and He-free (Type Ic) events thought to be associated with the deaths of massive stars. The exact nature of their progenitors is a matter of debate with several lines of evidence pointing towards intermediate mass (M-init < 20 M-circle dot) stars in binary systems, while in other cases they may be linked to single massiveWolf-Rayet stars. Here we present the analysis of the light curves of 34 SE SNe published by the Carnegie Supernova Project (CSP-I) that are unparalleled in terms of photometric accuracy and wavelength range. Light-curve parameters are estimated through the fits of an analytical function and trends are searched for among the resulting fit parameters. Detailed inspection of the dataset suggests a tentative correlation between the peak absolute B-band magnitude and Delta m(15)(B), while the post maximum light curves reveals a correlation between the late-time linear slope and Delta m(15). Making use of the full set of optical and near-IR photometry, combined with robust host-galaxy extinction corrections, comprehensive bolometric light curves are constructed and compared to both analytic and hydrodynamical models. This analysis finds consistent results among the two different modeling techniques and from the hydrodynamical models we obtained ejecta masses of 1.1-6.2 M-circle dot, Ni-56 masses of 0.03-0.35 M fi, and explosion energies (excluding two SNe Ic-BL) of 0.25-3.0 x 10(51) erg. Our analysis indicates that adopting kappa = 0.07 cm(2) g(-1) as the mean opacity serves to be a suitable assumption when comparing Arnett-model results to those obtained from hydrodynamical calculations. We also find that adopting He I and O I line velocities to infer the expansion velocity in He-rich and He-poor SNe, respectively, provides ejecta masses relatively similar to those obtained by using the Fe II line velocities, although the use of Fe II as a diagnostic does imply higher explosion energies. The inferred range of ejecta masses are compatible with intermediate mass (M-ZAMS <= 20 M-circle dot) progenitor stars in binary systems for the majority of SE SNe. Furthermore, our hydrodynamical modeling of the bolometric light curves suggests a significant fraction of the sample may have experienced significant mixing of 56Ni, particularly in the case of SNe Ic.

The type. Ia supernova (SN) 2012fr displayed an unusual combination of its Si II lambda lambda 5972, 6355 features. This includes the ratio of their pseudo-equivalent widths, placing it at the border of the shallow silicon (SS) and core normal (CN) spectral subtype in the Branch diagram, while the Si II lambda 6355 expansion velocities place it as a high-velocity (HV) object in the Wang et al. spectral type that most interestingly evolves slowly, placing it in the low-velocity gradient (LVG) typing of Benetti et al. Only 5% of SNe. Ia are HV and located in the SS+CN portion of the Branch diagram, and fewer than 10% of SNe. Ia are both HV and LVG. These features point toward SN. 2012fr being quite unusual, similar in many ways to the peculiar SN 2000cx. We modeled the spectral evolution of SN 2012fr to see if we could gain some insight into its evolutionary behavior. We use the parameterized radiative transfer code SYNOW to probe the abundance stratification of SN. 2012fr at pre-maximum, maximum, and post-maximum light epochs. We also use a grid of W7 models in the radiative transfer code PHOENIX to probe the effect of different density structures on the formation of the Si II lambda 6355 absorption feature at post-maximum epochs. We find that the unusual features observed in SN 2012fr are likely due to a shell-like density enhancement in the outer ejecta. We comment on possible reasons for atypical Ca II absorption features, and suggest that they are related to the Si II features.