Progenitors of type Ia supernovae

Type Ia supernovae (SNe Ia) play an important role in astrophysics and are crucial for the studies of stellar evolution, galaxy evolution and cosmology. They are generally thought to be thermonuclear explosions of accreting carbon–oxygen white dwarfs (CO WDs) in close binaries, however, the nature of the mass donor star is still unclear. In this article, we review various progenitor models proposed in the past years and summarize many observational results that can be used to put constraints on the nature of their progenitors. We also discuss the origin of SN Ia diversity and the impacts of SN Ia progenitors on some fields. The currently favourable progenitor model is the single-degenerate (SD) model, in which the WD accretes material from a non-degenerate companion star. This model may explain the similarities of most SNe Ia. It has long been argued that the double-degenerate (DD) model, which involves the merger of two CO WDs, may lead to an accretion-induced collapse rather than a thermonuclear explosion. However, recent observations of a few SNe Ia seem to support the DD model, and this model can produce normal SN Ia explosion under certain conditions. Additionally, the sub-luminous SNe Ia may be explained by the sub-Chandrasekhar mass model. At present, it seems likely that more than one progenitor model, including some variants of the SD and DD models, may be required to explain the observed diversity of SNe Ia.     

ROSAT observations of recent supernovae

Results from ROSAT observations of recent supernova events are discussed in the light of a model, where the soft X-rays originate in the shock interaction of the expanding supernova ejecta with the circumstellar material, left from heavy mass loss of the progenitor object. Special attention is given to the observations of SN1993J in M81, where lightcurves and spectral measurements allow a more detailed analysis and comparison to numerical model calculations.     

Constraints on cosmological anisotropy out to z= 1 from Type Ia supernovae

A combined sample of 79 high- and low-redshift Type Ia supernovae (SNe) is used to set constraints on the degree of anisotropy in the Universe out to z ≃1. First, we derive the global most probable values of matter density Ω_M, the cosmological constant Ω_Λ and the Hubble constant H ₀, and find them to be consistent with the published results from the two data sets of Riess et al. and Perlmutter et al. We then examine the Hubble diagram (HD, i.e., the luminosity–redshift relation) in different directions on the sky by utilizing spherical harmonic expansion. In particular, via the analysis of the dipole anisotropy, we divide the sky into the two hemispheres that yield the most discrepant of the three cosmological parameters, and the scatter χ _HD² in each case. The most discrepant values roughly move along the locus −4Ω_M+3Ω_Λ=1 (cf. Perlmutter et al.), but by no more than Δ≈2.5 along this line. For a perfect Friedmann–Robertson–Walker universe, Monte Carlo realizations that mimic the current set of SNe yield values higher than the measured Δ in ∼1/5 of the cases (for Ω_M). We discuss implications for the validity of the Cosmological Principle, and possible calibration problems in the SNe data sets.     

Investigation of burning in type Ia supernovae

Type Ia supernovae are important cosmological objects that have played a major role in determining the composition of the Universe. Despite four decades of studies, there is no complete understanding of the explosion mechanism. One of the main problems consists in describing the burning wave propagation through the presupernova, a white dwarf. It is well known from observations that an initially slow flame accelerates and transforms into detonation as it moves. The acceleration mechanism realized in supernovae is not yet known, but it is believed to occur through various instabilities. The Landau-Darrieus instability of a thin deflagration thermonuclear burning front propagating through the presupernova is investigated. Direct numerical simulations of burning by the level-set method are presented. Small perturbations at the front are shown to merge into one large cusp after some time. As a flame with limited sizes moves, this leads only to a slight increase in the velocity, which does not allow it to accelerate to the speed of sound.     

Mass-accreting white dwarfs and type Ia supernovae

Type Ia supernovae(SNe Ia) play a prominent role in understanding the evolution of the Universe. They are thought to be thermonuclear explosions of mass-accreting carbon-oxygen white dwarfs(CO WDs) in binaries, although the mass donors of the accreting WDs are still not well determined. In this article, I review recent studies on mass-accreting WDs, including H-and He-accreting WDs. I also review currently most studied progenitor models of SNe Ia, i.e., the single-degenerate model(including the WD+MS channel, the WD+RG channel and the WD+He star channel), the doubledegenerate model(including the violent merger scenario) and the sub-Chandrasekhar mass model.Recent progress on these progenitor models is discussed, including the initial parameter space for producing SNe Ia, the binary evolutionary paths to SNe Ia, the progenitor candidates for SNe Ia, the possible surviving companion stars of SNe Ia, some observational constraints, etc. Some other potential progenitor models of SNe Ia are also summarized, including the hybrid CONe WD model, the core-degenerate model, the double WD collision model, the spin-up/spin-down model and the model of WDs near black holes. To date, it seems that two or more progenitor models are needed to explain the observed diversity among SNe Ia.     

The cooling time of white dwarfs produced from type Ia supernovae

Type Ia supernovae(SNe Ia)play a key role in measuring cosmological parameters,in which the Phillips relation is adopted.However,the origin of the relation is still unclear.Several parameters are suggested,e.g.the relative content of carbon to oxygen(C/O)and the central density of the white dwarf(WD)at ignition.These parameters are mainly determined by the WD's initial mass and its cooling time,respectively.Using the progenitor model developed by Meng & Yang,we present the distributions of the initial WD mass and the cooling time.We do not find any correlation between these parameters.However,we notice that as the range of the WD's mass decreases,its average value increases with the cooling time.These results could provide a constraint when simulating the SN Ia explosion,i.e.the WDs with a high C/O ratio usually have a lower central density at ignition,while those having the highest central density at ignition generally have a lower C/O ratio.The cooling time is mainly determined by the evolutionary age of secondaries,and the scatter of the cooling time decreases with the evolutionary age.Our results may indicate that WDs with a long cooling time have more uniform properties than those with a short cooling time,which may be helpful to explain why SNe Ia in elliptical galaxies have a more uniform maximum luminosity than those in spiral galaxies.     

The absolute infrared magnitudes of type Ia supernovae

The absolute luminosities and homogeneity of early-time infrared (IR) light curves of type Ia supernovae are examined. Eight supernovae are considered. These are selected to have accurately known epochs of maximum blue light as well as having reliable distance estimates and/or good light curve coverage. Two approaches to extinction correction are considered. Owing to the low extinction in the IR, the differences in the corrections via the two methods are small. Absolute magnitude light curves in the J , H and K bands are derived. Six of the events, including five established 'branch-normal' supernovae, show similar coeval magnitudes. Two of these, supernovae (SNe) 1989B and 1998bu, were observed near maximum infrared light. This occurs about 5 d before maximum blue light. Absolute peak magnitudes of about −19.0, −18.7 and −18.8 in J , H and K respectively were obtained. The two spectroscopically peculiar supernovae in the sample, SNe 1986G and 1991T, also show atypical IR behaviour. The light curves of the six similar supernovae can be represented fairly consistently with a single light curve in each of the three bands. In all three IR bands the dispersion in absolute magnitude is about 0.15 mag, and this can be accounted for within the uncertainties of the individual light curves. No significant variation of absolute IR magnitude with B -band light curve decline rate, Δ m ₁₅( B ), is seen over the range 0.87<Δ m ₁₅( B )<1.31. However, the data are insufficient to allow us to decide whether or not the decline rate relation is weaker in the IR than in the optical region. IR light curves of type Ia supernovae should eventually provide cosmological distance estimates that are of equal, or even superior, quality to those obtained in optical studies.     

Double-detonation model of type Ia supernovae with a variable helium layer ignition mass

Although Type Ia supernovae(SNe Ia) play an important role in the study of cosmology, their progenitors are still poorly understood. Thermonuclear explosions from the helium double-detonation sub-Chandrasekhar mass model have been considered as an alternative method for producing SNe Ia. By adopting the assumption that a double detonation occurs when a He layer with a critical ignition mass accumulates on the surface of a carbon–oxygen white dwarf(CO WD), we perform detailed binary evolution calculations for the He double-detonation model, in which a He layer from a He star accumulates on a CO WD. According to these calculations, we obtain the initial parameter spaces for SNe Ia in the orbital period and secondary mass plane for various initial WD masses. We implement these results into a detailed binary population synthesis approach to calculate SN Ia birthrates and delay times. From this model,the SN Ia birthrate in our Galaxy is ～0.4- 1.6 × 10-3yr-1. This indicates that the double-detonation model only produces part of the SNe Ia. The delay times from this model are ～ 70- 710 Myr, which contribute to the young population of SNe Ia in the observations. We found that the CO WD + sdB star system CD-30 11223 could produce an SN Ia via the double-detonation model in its future evolution.     

Revisiting the magnification of type Ia supernovae with SDSS

We cross-correlate the sample of type Ia supernovae from Riess A. G. et al. with the SDSS DR2 photometric galaxy catalogue. In contrast to recent work, we find no detectable correlation between supernova magnitude and galaxy overdensity on scales ranging between 1 and 10 arcmin. Our results are in accord with theoretical expectations for gravitational lensing of supernovae by large-scale structure. Future supernova surveys such as SNAP will be capable of detecting unambiguously the predicted lensing signal.     

Gravitational lensing of type Ia supernovae by galaxy clusters

We propose a method to remove the mass-sheet degeneracy that arises when the mass of galaxy clusters is inferred from gravitational shear. The method utilizes high-redshift standard candles that undergo weak lensing. Natural candidates for such standard candles are type Ia supernovae (SNe Ia).
When corrected with the light-curve shape (LCS), the peak magnitude of SNe Ia provides a standard candle with an uncertainty in apparent magnitude of Δ m ≃0.1–0.2. Gravitational magnification of a background SN Ia by an intervening cluster would cause a mismatch between the observed SN Ia peak magnitude compared with that expected from its LCS and redshift. The average detection rate for SNe Ia with a significant mismatch of ≥2Δ m behind a cluster at z ≃0.05–0.15 is about 1–2 supernovae per cluster per year at J , I , R ≲25–26.
Since SNe are point-like sources for a limited period, they can experience significant microlensing by massive compact halo objects (MACHOs) in the intracluster medium. Microlensing events caused by MACHOs of ∼10⁻⁴ M⊙ are expected to have time-scales similar to that of the SN light curve. Both the magnification curve by a MACHO and the light curve of a SN Ia have characteristic shapes that allow us to separate them. Microlensing events caused by MACHOs of smaller mass can unambiguously be identified in the SN light curve if the latter is continuously monitored. The average number of identifiable microlensing events per nearby cluster ( z ≲0.05) per year is ∼0.02 ( f /0.01), where f is the fraction of the cluster mass in MACHOs of masses 10⁻⁷< M _macho/M⊙<10⁻⁴.     

Gamma-rays as probes for the multi-dimensionality of type Ia supernovae

We present γ-ray spectra for a set of Type Ia supernovae. Our study is based on a detailed Monte Carlo transport scheme for both spherical and full 3-D geometries. Classical and new challenges of the γ-ray astronomy are addressed. We find that γ-rays are very suitable to reveal the structure of the envelope and, thus, they allow to probe properties of the nuclear burning front and the progenitor, namely its central density and global asphericities. The potential problems are discussed for the quantitative comparison between theoretical and observed line fluxes during the first few months after the explosion.     

Testing the distance-duality relation with data from galaxy clusters and type Ia supernovae

We test the distance-duality(DD) relation by combining the angular diameter distance DA provided by two galaxy cluster samples compiled by De Filippis et al.(the elliptical β model) and Bonamente et al.(the spherical β model),and the luminosity distance DL from Constitution and Union2 type Ia supernova(SNe Ia) datasets. To obtain DL associated with the observed DA at the same redshift,we smooth the noise of the SNe Ia in a model-independent way,obtain the evolutionary curve of DL and,finally,test the DD rel...     

On the non-Gaussian errors in high-z supernovae type Ia data

The nature of random errors in any data set is Gaussian, which is a well established fact according to the Central Limit Theorem. Supernovae type Ia data have played a crucial role in major discoveries in cosmology. Unlike in laboratory experiments, astronomical measurements cannot be performed in controlled situations. Thus, errors in astronomical data can be more severe in terms of systematics and non-Gaussianity compared to those of laboratory experiments. In this paper, we use the Kolmogorov-Smirnov statistic to test non-Gaussianity in high-z supernovae data. We apply this statistic to four data sets, i.e., Gold data(2004),Gold data(2007), the Union2 catalog and the Union2.1 data set for our analysis. Our results show that in all four data sets the errors are consistent with a Gaussian distribution.     

WD+RG systems as the progenitors of type Ia supernovae

Type Ia supernovae(SNe Ia)play an important role in the study of cosmic evolution,especially in cosmology.There are several progenitor models for SNe Ia proposed in the past years.By considering the effect of accretion disk instability on the evolution of white dwarf(WD)binaries,we performed detailed binary evolution calculations for the WD+red-giant(RG)channel of SNe Ia,in which a carbon-oxygen WD accretes material from a RG star to increase its mass to the Chandrasekhar mass limit.According to these calcu...     

Cosmological parameters from velocities, cosmic microwave background and supernovae

We compare and combine likelihood functions of the cosmological parameters Ω_m, h and σ ₈, from peculiar velocities, cosmic microwave background (CMB) and type Ia supernovae. These three data sets directly probe the mass in the Universe, without the need to relate the galaxy distribution to the underlying mass via a 'biasing' relation. We include the recent results from the CMB experiments BOOMERANG and MAXIMA-1. Our analysis assumes a flat Λ cold dark matter (ΛCDM) cosmology with a scale-invariant adiabatic initial power spectrum and baryonic fraction as inferred from big-bang nucleosynthesis. We find that all three data sets agree well, overlapping significantly at the 2 σ level. This therefore justifies a joint analysis, in which we find a joint best-fitting point and 95 per cent confidence limits of     (0.17,0.39),     (0.64,0.86) and     (0.98,1.37). In terms of the natural parameter combinations for these data     (0.40,0.73),     (0.16,0.27). Also for the best-fitting point,     and the age of the Universe is 13.2 Gyr.