G. Smadja

NEARBY SUPERNOVA FACTORY OBSERVATIONS OF SN 2007if: FIRST TOTAL MASS MEASUREMENT OF A SUPER-CHANDRASEKHAR-MASS PROGENITOR

We present photometric and spectroscopic observations of SN 2007if, an overluminous (M_V = –20.4), red (B – V = 0.16 at B-band maximum), slow-rising (t_(rise) = 24 days) type Ia supernova (SN Ia) in a very faint (M_g = –14.10) host galaxy. A spectrum at 5 days past B-band maximum light is a direct match to the super-Chandrasekhar-mass candidate SN Ia 2003fg, showing Si II and C II at ~9000 km s^(–1). A high signal-to-noise co-addition of the SN spectral time series reveals no Na I D absorption, suggesting negligible reddening in the host galaxy, and the late-time color evolution has the same slope as the Lira relation for normal SNe Ia. The ejecta appear to be well mixed, with no strong maximum in I band and a diversity of iron-peak lines appearing in near-maximum-light spectra. SN 2007if also displays a plateau in the Si II velocity extending as late as +10 days, which we interpret as evidence for an overdense shell in the SN ejecta. We calculate the bolometric light curve of the SN and use it and the Si II velocity evolution to constrain the mass of the shell and the underlying SN ejecta, and demonstrate that SN 2007if is strongly inconsistent with a Chandrasekhar-mass scenario. Within the context of a tamped detonation model appropriate for double-degenerate mergers, and assuming no host extinction, we estimate the total mass of the system to be 2.4 ± 0.2 M_☉, with 1.6 ± 0.1 M_☉ of ^(56)Ni and with 0.3-0.5 M_☉ in the form of an envelope of unburned carbon/oxygen. Our modeling demonstrates that the kinematics of shell entrainment provide a more efficient mechanism than incomplete nuclear burning for producing the low velocities typical of super-Chandrasekhar-mass SNe Ia.

Constraining type Ia supernova models: SN 2011fe as A test case

The nearby supernova SN 2011fe can be observed in unprecedented detail. Therefore, it is an important test case for Type Ia supernova (SN Ia) models, which may bring us closer to understanding the physical nature of these objects. Here, we explore how available and expected future observations of SN 2011fe can be used to constrain SN Ia explosion scenarios. We base our discussion on three-dimensional simulations of a delayed detonation in a Chandrasekhar-mass white dwarf and of a violent merger of two white dwarfs (WDs)—realizations of explosion models appropriate for two of the most widely discussed progenitor channels that may give rise to SNe Ia. Although both models have their shortcomings in reproducing details of the early and near-maximum spectra of SN 2011fe obtained by the Nearby Supernova Factory (SNfactory), the overall match with the observations is reasonable. The level of agreement is slightly better for the merger, in particular around maximum, but a clear preference for one model over the other is still not justified. Observations at late epochs, however, hold promise for discriminating the explosion scenarios in a straightforward way, as a nucleosynthesis effect leads to differences in the 55Co production. SN 2011fe is close enough to be followed sufficiently long to study this effect.

Spectrophotometric time series of SN 2011fe from the Nearby Supernova Factory

We present 32 epochs of optical (3300‐9700 A) spectrophotometric observations of the nearby quintessential “normal” type Ia supernova (SN Ia) SN 2011fe in the galaxy M101, extending from 15 to + 97 d with respect to B-band maximum, obtained by the Nearby Supernova Factory collaboration. SN 2011fe is the closest ( = 29:04) and brightest (Bmax = 9:94 mag) SN Ia observed since the advent of modern large scale programs for the intensive periodic followup of supernovae. Both synthetic light curve measurements and spectral feature analysis attest to the normality of SN 2011fe. There is very little evidence for reddening in its host galaxy. The homogeneous calibration, intensive time sampling, and high signal-to-noise ratio of the data set make it unique. Thus it is ideal for studying the physics of SN Ia explosions in detail, and for furthering the use of SNe Ia as standardizable candles for cosmology. Several such applications are shown, from the creation of a bolometric light curve and measurement of the 56 Ni mass, to the simulation of detection thresholds for unburned carbon, direct comparisons with other SNe Ia, and existing spectral templates.

The reddening law of type Ia supernovae: separating intrinsic variability from dust using equivalent widths

We employ 76 type Ia supernovae (SNe Ia) with optical spectrophotometry within 2.5 days of B-band maximum light obtained by the Nearby Supernova Factory to derive the impact of Si and Ca features on the supernovae intrinsic luminosity and determine a dust reddening law. We use the equivalent width of Si II λ4131 in place of the light curve stretch to account for first-order intrinsic luminosity variability. The resulting empirical spectral reddening law exhibits strong features that are associated with Ca II and Si II λ6355. After applying a correction based on the Ca II H&K equivalent width we find a reddening law consistent with a Cardelli extinction law. Using the same input data, we compare this result to synthetic rest-frame UBVRI-like photometry to mimic literature observations. After corrections for signatures correlated with Si II λ4131 and Ca II H&K equivalent widths and introducing an empirical correlation between colors, we determine the dust component in each band. We find a value of the total-to-selective extinction ratio, R v = 2.8 ± 0.3. This agrees with the Milky Way value, in contrast to the low R v values found in most previous analyses. This result suggests that the long-standing controversy in interpreting SN Ia colors and their compatibility with a classical extinction law, which is critical to their use as cosmological probes, can be explained by the treatment of the dispersion in colors, and by the variability of features apparent in SN Ia spectra.

Using spectral flux ratios to standardize SN Ia luminosities

We present a new method to standardize typexa0Ia supernova (SNxa0Ia) luminosities to

Type Ia Supernova Carbon Footprints

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HOST GALAXY PROPERTIES AND HUBBLE RESIDUALS OF TYPE Ia SUPERNOVAE FROM THE NEARBY SUPERNOVA FACTORY

0.13xa0mag using flux ratios from a single flux-calibrated spectrum per SN. Using Nearby Supernova Factory spectrophotomery of 58xa0SNexa0Ia, we performed an unbiased search for flux ratios that correlate with SNxa0Ia luminosity. After developing the method and selecting the best ratios from a training sample, we verified the results on a separate validation sample and with data from the literature. We identified multiple flux ratios whose correlations with luminosity are stronger than those of light curve shape and color, previously identified spectral feature ratios, or equivalent width measurements. In particular, the flux ratio

Evidence of environmental dependencies of Type Ia supernovae from the Nearby Supernova Factory indicated by local H alpha

mathcal{R}_{642/443} = F(642~{rm nm}) / F(443~{rm nm})

Type Ia supernova bolometric light curves and ejected mass estimates from the Nearby Supernova Factory

has a correlation ofxa00.95 with SNxa0Ia absolute magnitudes. Using this single ratio as a correction factor produces a Hubble diagram with a residual scatter standard deviation of

Atmospheric extinction properties above Mauna Kea from the Nearby SuperNova Factory spectro-photometric data set

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