[en] 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 ($t_{B_{max}}$). Supplementary imaging at the earliest epochs reveals an initial slow and nearly linear rise in luminosity with a duration of ~2.5 days, followed by a faster rising phase that is well reproduced by an explosion model with a moderate amount of 56 Ni 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 (λ >1800) 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_⊙ of ⁵⁶Ni 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 λ6355 line at ~12,000 km s^-1 that began ~5 days before $t_{B_{max}}$. 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.

[en] We present a new photometric identification technique for SN 1991bg-like type Ia supernovae (SNe Ia), i.e., objects with light curve characteristics such as later primary maxima and the absence of a secondary peak in redder filters. This method is capable of selecting this sub-group from the normal type Ia population. Furthermore, we find that recently identified peculiar sub-types such as SNe Iax and super-Chandrasekhar SNe Ia have photometric characteristics similar to 91bg-like SNe Ia, namely, the absence of secondary maxima and shoulders at longer wavelengths, and can also be classified with our technique. The similarity of these different SN Ia sub-groups perhaps suggests common physical conditions. This typing methodology permits the photometric identification of peculiar SNe Ia in large upcoming wide-field surveys either to study them further or to obtain a pure sample of normal SNe Ia for cosmological studies.

[en] An analysis of the first set of low-redshift (z < 0.08) Type Ia supernovae (SNe Ia) monitored by the Carnegie Supernova Project between 2004 and 2006 is presented. The data consist of well-sampled, high-precision optical (ugriBV) and near-infrared (NIR; YJHK_s ) light curves in a well-understood photometric system. Methods are described for deriving light-curve parameters, and for building template light curves which are used to fit SN Ia data in the ugriBVYJH bands. The intrinsic colors at maximum light are calibrated using a subsample of supernovae (SNe) assumed to have suffered little or no reddening, enabling color excesses to be estimated for the full sample. The optical-NIR color excesses allow the properties of the reddening law in the host galaxies to be studied. A low average value of the total-to-selective absorption coefficient, R_V ∼ 1.7, is derived when using the entire sample of SNe. However, when the two highly reddened SNe (SN 2005A and SN 2006X) in the sample are excluded, a value R_V ∼ 3.2 is obtained, similar to the standard value for the Galaxy. The red colors of these two events are well matched by a model where multiple scattering of photons by circumstellar dust steepens the effective extinction law. The absolute peak magnitudes of the SNe are studied in all bands using a two-parameter linear fit to the decline rates and the colors at maximum light, or alternatively, the color excesses. In both cases, similar results are obtained with dispersions in absolute magnitudes of 0.12-0.16 mag, depending on the specific filter-color combination. In contrast to the results obtained from the comparison of the color excesses, these fits of absolute magnitude give R_V ∼ 1-2 when the dispersion is minimized, even when the two highly reddened SNe are excluded. This discrepancy suggests that, beyond the 'normal' interstellar reddening produced in the host galaxies, there is an intrinsic dispersion in the colors of SNe Ia which is correlated with luminosity but independent of the decline rate. Finally, a Hubble diagram for the best-observed subsample of SNe is produced by combining the results of the fits of absolute magnitude versus decline rate and color excess for each filter. The resulting scatter of 0.12 mag appears to be limited by the peculiar velocities of the host galaxies as evidenced by the strong correlation between the distance-modulus residuals observed in the individual filters. The implication is that the actual precision of SNe Ia distances is 3%-4%.

[en] In providing an independent measure of the expansion history of the universe, the Carnegie Supernova Project (CSP) has observed 71 high-z Type Ia supernovae (SNe Ia) in the near-infrared bands Y and J. These can be used to construct rest-frame i-band light curves which, when compared to a low-z sample, yield distance moduli that are less sensitive to extinction and/or decline-rate corrections than in the optical. However, working with NIR observed and i-band rest-frame photometry presents unique challenges and has necessitated the development of a new set of observational tools in order to reduce and analyze both the low-z and high-z CSP sample. We present in this paper the methods used to generate uBVgriYJH light-curve templates based on a sample of 24 high-quality low-z CSP SNe. We also present two methods for determining the distances to the hosts of SN Ia events. A larger sample of 30 low-z SNe Ia in the Hubble flow is used to calibrate these methods. We then apply the method and derive distances to seven galaxies that are so nearby that their motions are not dominated by the Hubble flow.

[en] We present optical photometry and spectroscopy of the Type Ia supernova SN2018cqj/ATLAS18qtd. The supernova exploded in an isolated region at ∼65 kpc from the S0 galaxy IC 550 at z = 0.0165 (D ≈ 74 Mpc) and has a redshift consistent with a physical association to this galaxy. Multicolor photometry show that SN2018cqj/ATLAS18qtd is a low-luminosity ($M_{B_{max}}\approx <!--\; ???\; -->-<!--\; ???\; -->17.9$ mag), fast-declining Type Ia, with color stretch s _BV ≈ 0.6 and B-band decline rate Δm ₁₅(B) ≈ 1.77 mag. Two nebular-phase spectra obtained as part of the 100IAS survey at +193 and +307 days after peak show the clear detection of a narrow Hα line in emission that is resolved in the first spectrum with FWHM ≈ 1200 km s⁻¹ and L _Hα ≈ 3.8 × 10³⁷ erg s⁻¹. The detection of a resolved Hα line with a declining luminosity is broadly consistent with recent models where hydrogen is stripped from the nondegenerate companion in a single-degenerate progenitor system. However, the amount of hydrogen consistent with the luminosities of the Hα line would be ∼10⁻³ M _⊙, which is significantly less than theoretical model predictions in the classical single-degenerate progenitor systems. SN2018cqj/ATLAS18qtd is the second low-luminosity, fast-declining SN Ia after SN2018fhw/ASASSN-18tb that shows narrow Hα in emission in its nebular-phase spectra.

[en] The Carnegie Supernova Project (CSP) is a five-year survey being carried out at the Las Campanas Observatory to obtain high-quality light curves of ∼100 low-redshift Type Ia supernovae (SNe Ia) in a well-defined photometric system. Here we present the first release of photometric data that contains the optical light curves of 35 SNe Ia, and near-infrared light curves for a subset of 25 events. The data comprise 5559 optical (ugriBV) and 1043 near-infrared (Y JHK_s ) data points in the natural system of the Swope telescope. Twenty-eight SNe have pre-maximum data, and for 15 of these, the observations begin at least 5 days before B maximum. This is one of the most accurate data sets of low-redshift SNe Ia published to date. When completed, the CSP data set will constitute a fundamental reference for precise determinations of cosmological parameters, and serve as a rich resource for comparison with models of SNe Ia.

[en] Ultraviolet, optical, and near-infrared photometry and optical spectroscopy of the broad-lined Type Ic supernova (SN) 2009bb are presented, following the flux evolution from -10 to +285 days past B-band maximum. Thanks to the very early discovery, it is possible to place tight constraints on the SN explosion epoch. The expansion velocities measured from near maximum spectra are found to be only slightly smaller than those measured from spectra of the prototype broad-lined SN 1998bw associated with GRB 980425. Fitting an analytical model to the pseudobolometric light curve of SN 2009bb suggests that 4.1 ± 1.9 M_sun of material was ejected with 0.22 ± 0.06 M_sun of it being ⁵⁶Ni. The resulting kinetic energy is 1.8 ± 0.7 x 10⁵² erg. This, together with an absolute peak magnitude of M_B = -18.36 ± 0.44, places SN 2009bb on the energetic and luminous end of the broad-lined Type Ic (SN Ic) sequence. Detection of helium in the early time optical spectra accompanied with strong radio emission and high metallicity of its environment makes SN 2009bb a peculiar object. Similar to the case for gamma-ray bursts (GRBs), we find that the bulk explosion parameters of SN 2009bb cannot account for the copious energy coupled to relativistic ejecta, and conclude that another energy reservoir (a central engine) is required to power the radio emission. Nevertheless, the analysis of the SN 2009bb nebular spectrum suggests that the failed GRB detection is not imputable to a large angle between the line-of-sight and the GRB beamed radiation. Therefore, if a GRB was produced during the SN 2009bb explosion, it was below the threshold of the current generation of γ-ray instruments.

[en] We present an updated analysis of the intrinsic colors of Type Ia supernova (SNe Ia) using the latest data release of the Carnegie Supernova Project. We introduce a new light-curve parameter very similar to stretch that is better suited for fast-declining events, and find that these peculiar types can be seen as extensions to the population of 'normal' SNe Ia. With a larger number of objects, an updated fit to the Lira relation is presented along with evidence for a dependence on the late-time slope of the B – V light-curves with stretch and color. Using the full wavelength range from u to H band, we place constraints on the reddening law for the sample as a whole and also for individual events/hosts based solely on the observed colors. The photometric data continue to favor low values of R_V , though with large variations from event to event, indicating an intrinsic distribution. We confirm the findings of other groups that there appears to be a correlation between the derived reddening law, R_V , and the color excess, E(B – V), such that larger E(B – V) tends to favor lower R_V . The intrinsic u-band colors show a relatively large scatter that cannot be explained by variations in R_V or by the Goobar power-law for circumstellar dust, but rather is correlated with spectroscopic features of the supernova and is therefore likely due to metallicity effects.

[en] The Carnegie Supernova Project (CSP) is designed to measure the luminosity distance for Type Ia supernovae (SNe Ia) as a function of redshift, and to set observational constraints on the dark energy contribution to the total energy content of the universe. The CSP differs from other projects to date in its goal of providing an I-band rest-frame Hubble diagram. Here, we present the first results from near-infrared observations obtained using the Magellan Baade telescope for SNe Ia with 0.1 < z < 0.7. We combine these results with those from the low-redshift CSP at z < 0.1. In this paper, we describe the overall goals of this long-term program, the observing strategy, data reduction procedures, and treatment of systematic uncertainties. We present light curves and an I-band Hubble diagram for this first sample of 35 SNe Ia, and we compare these data to 21 new SNe Ia at low redshift. These data support the conclusion that the expansion of the universe is accelerating. When combined with independent results from baryon acoustic oscillations, these data yield Ω _m = 0.27 ± 0.02(statistical) and Ω_DE = 0.76 ± 0.13(statistical) ± 0.09(systematic), for the matter and dark energy densities, respectively. If we parameterize the data in terms of an equation of state, w (with no time dependence), assume a flat geometry, and combine with baryon acoustic oscillations, we find that w = -1.05 ± 0.13(statistical) ± 0.09(systematic). The largest source of systematic uncertainty on w arises from uncertainties in the photometric calibration, signaling the importance of securing more accurate photometric calibrations for future supernova cosmology programs. Finally, we conclude that either the dust affecting the luminosities of SNe Ia has a different extinction law (R_V = 1.8) than that in the Milky Way (where R_V = 3.1), or that there is an additional intrinsic color term with luminosity for SNe Ia, independent of the decline rate. Understanding and disentangling these effects is critical for minimizing the systematic uncertainties in future SN Ia cosmology studies.

[en] We present near-infrared (NIR) spectroscopic and photometric observations of the nearby Type Ia SN 2014J. The 17 NIR spectra span epochs from +15.3 to +92.5 days after B-band maximum light, while the ${JHK}_s$ photometry include epochs from −10 to +71 days. These data are used to constrain the progenitor system of SN 2014J utilizing the Paβ line, following recent suggestions that this phase period and the NIR in particular are excellent for constraining the amount of swept-up hydrogen-rich material associated with a non-degenerate companion star. We find no evidence for Paβ emission lines in our post-maximum spectra, with a rough hydrogen mass limit of $\lesssim <!--\; ???\; -->0.1$ M _⊙, which is consistent with previous limits in SN 2014J from late-time optical spectra of the Hα line. Nonetheless, the growing data set of high-quality NIR spectra holds the promise of very useful hydrogen constraints.