SNIa Observations Research Articles

Hubble tension and gravitational self-interaction

One of the most important problems vexing the ΛCDM cosmological model is the Hubble tension. It arises from the fact that measurements of the present value of the Hubble parameter performed with low-redshift quantities, e.g. the Type IA supernova, tend to yield larger values than measurements from quantities originating at high-redshift, e.g. fits of cosmic microwave background radiation. It is becoming likely that the discrepancy, currently standing at 5σ, is not due to systematic errors in the measurements. Here we explore whether the self-interaction of gravitational fields in General Relativity, which are traditionally neglected when studying the evolution of the Universe, can contribute to explaining the tension. We find that with field self-interaction accounted for, both low- and high-redshift data are simultaneously well-fitted, thereby showing that gravitational self-interaction yield consistent H 0 values when inferred from SnIA and cosmic microwave background observations. Crucially, this is achieved without introducing additional parameters.

JWST MIRI/Medium Resolution Spectrograph (MRS) Observations and Spectral Models of the Underluminous Type Ia Supernova 2022xkq

We present a JWST mid-infrared (MIR) spectrum of the underluminous Type Ia Supernova (SN Ia) 2022xkq, obtained with the medium-resolution spectrometer on the Mid-Infrared Instrument (MIRI) ∼130 days post-explosion. We identify the first MIR lines beyond 14 μm in SN Ia observations. We find features unique to underluminous SNe Ia, including the following: isolated emission of stable Ni, strong blends of [Ti ii], and large ratios of singly ionized to doubly ionized species in both [Ar] and [Co]. Comparisons to normal-luminosity SNe Ia spectra at similar phases show a tentative trend between the width of the [Co iii] 11.888 μm feature and the SN light-curve shape. Using non-LTE-multi-dimensional radiation hydro simulations and the observed electron capture elements, we constrain the mass of the exploding WD. The best-fitting model shows that SN 2022xkq is consistent with an off-center delayed-detonation explosion of a near-Chandrasekhar mass WD ( MWD ≈1.37 M ⊙) of high central density (ρ c ≥ 2.0 × 109 g cm−3) seen equator-on, which produced M(56Ni) =0.324 M ⊙ and M(58Ni) ≥0.06 M ⊙. The observed line widths are consistent with the overall abundance distribution; and the narrow stable Ni lines indicate little to no mixing in the central regions, favoring central ignition of subsonic carbon burning followed by an off-center deflagration-to-detonation transition beginning at a single point. Additional observations may further constrain the physics revealing the presence of additional species including Cr and Mn. Our work demonstrates the power of using the full coverage of MIRI in combination with detailed modeling to elucidate the physics of SNe Ia at a level not previously possible.

SALT3-NIR: Taking the Open-source Type Ia Supernova Model to Longer Wavelengths for Next-generation Cosmological Measurements

A large fraction of Type Ia supernova (SN Ia) observations over the next decade will be in the near-infrared (NIR), at wavelengths beyond the reach of the current standard light-curve model for SN Ia cosmology, SALT3 (∼2800–8700 Å central filter wavelength). To harness this new SN Ia sample and reduce future light-curve standardization systematic uncertainties, we train SALT3 at NIR wavelengths (SALT3-NIR) up to 2 μm with the open-source model-training software SALTshaker, which can easily accommodate future observations. Using simulated data, we show that the training process constrains the NIR model to ∼2%–3% across the phase range (−20 to 50 days). We find that Hubble residual (HR) scatter is smaller using the NIR alone or optical+NIR compared to optical alone, by up to ∼30% depending on filter choice (95% confidence). There is significant correlation between NIR light-curve stretch measurements and luminosity, with stretch and color corrections often improving HR scatter by up to ∼20%. For SN Ia observations expected from the Roman Space Telescope, SALT3-NIR increases the amount of usable data in the SALT framework by ∼20% at redshift z ≲ 0.4 and by ∼50% at z ≲ 0.15. The SALT3-NIR model is part of the open-source SNCosmo and SNANA SN Ia cosmology packages.

Misinterpreting modified gravity as dark energy: a quantitative study

Standard cosmological data analyses typically constrain simple phenomenological dark-energy parameters, for example the present-day value of the equation of state parameter, w 0, and its variation with scale factor, w a. However, results from such an analysis cannot easily indicate the presence of modified gravity. Even if general relativity does not hold, experimental data could still be fit sufficiently well by a phenomenological w 0 w aCDM, unmodified-gravity model. Hence, it would be very useful to know if there are generic signatures of modified gravity in standard analyses. Here we present, for the first time to our knowledge, a quantitative mapping showing how modified gravity models look when (mis)interpreted within the standard unmodified-gravity analysis. Scanning through a broad space of modified-gravity (Horndeski) models, and assuming a near-future survey consisting of CMB, BAO, and SNIa observations, we report values of the best-fit set of cosmological parameters including (w 0, w a) that would be inferred if modified gravity were at work. We find that modified gravity models that can masquerade as standard gravity lead to very specific biases in standard-parameter spaces. We also comment on implications for measurements of the amplitude of mass fluctuations described by the parameter S 8.

Cosmological Model-independent Constraints on Spatial Curvature from Strong Gravitational Lensing and SN Ia Observations

Abstract Applying the distance sum rule in strong gravitational lensing (SGL) and SN Ia observations, one can provide an interesting cosmological model-independent method to determine the cosmic curvature parameter Ω k . In this paper, with the newly compiled data sets including 161 galactic-scale SGL systems and 1048 SN Ia data, we place constraints on Ω k within the framework of three types of lens models extensively used in SGL studies. Moreover, to investigate the effect of different mass lens samples on the results, we divide the SGL sample into three subsamples based on the center velocity dispersion of intervening galaxies. In the singular isothermal sphere (SIS) and extended power-law lens models, a flat universe is supported with an uncertainty of about 0.2, while a closed universe is preferred in the power-law lens model. We find that the choice of lens models and the classification of SGL data actually can influence the constraints on Ω k significantly.

Constraints on a scalar-tensor model with Gauss–Bonnet coupling from SN Ia and BAO observations

In the present work, the observational consequences of a subclass of of the Horndeski theory have been investigated. In this theory a scalar field (tachyon field) non-minimally coupled to the Gauss-Bonnet invariant through an arbitrary function of the scalar field. By considering a spatially flat FRW universe, the free parameters of the model have been constrained using a joint analysis from observational data of the Type Ia supernovae and Baryon Acoustic Oscillations measurements. The best fit values obtained from these datasets are then used to reconstruct the equation of state parameter of the scalar field. The results show the phantom, quintessence and phantom divide line crossing behavior of the equation of state and also cosmological viability of the model.

Robust and model-independent cosmological constraints from distance measurements

We present a systematic analysis of the cosmological constraints from the “Pantheon Sample” of 1048 Type Ia Supernovae (SNe Ia) in the redshift range 0.01<z<2.3 compiled by Scolnic et al. (2018). Applying the flux-averaging method for detecting unknown systematic effects, we find that the “Pantheon” sample has been well calibrated and the bias caused by unknown systematic errors has been minimized. We present the estimate of distances measured from SNe Ia and reconstruct the expansion history of the Universe. The results are in agreement with a simple cosmological constant model and reveals the possible improvements that future SN Ia observations from WFIRST and LSST can target. We have derived distance priors using the Cosmic Microwave Background (CMB) data from the Planck 2018 final data release, and combine them with SNe Ia and baryon acoustic oscillation (BAO) data, to explore the impact from the systematic errors of SNe Ia on the combined cosmological parameter constraints. Using the combined data set of SNe Ia, BAO, and CMB distance priors, we measure the dark energy density function X(z)=ρX(z)/ρX(0) as a free function (defined as a cubic spline of its values at z=0.33, 0.67, 1.0), along with the cosmological parameters (Ωk, Ωm, Ωb, H0). We find no deviation from a flat Universe dominated by a cosmological constant (X(z)=1), and H0=68.4± 0.9 km s−1Mpc−1, straddling the Planck team's measurement of H0=67.4± 0.5 km s−1Mpc−1, and Riess et al. (2018) measurement of H0=73.52± 1.62 km s−1Mpc−1. Adding H0=73.52± 1.62 km s−1Mpc−1 as a prior to the combined data set leads to the time dependence of the dark energy density at z∼ 0.33 at 68% confidence level. Not including the systematic errors on SNe Ia has a similar but larger effect on the dark energy density measurement.

Constraining Type Ia supernova asymmetry with the gamma-ray escape time-scale

We calculate the effects of an asymmetric $^{56}\mathrm{Ni}$ distribution in Type Ia supernova (SN Ia) ejecta on the gamma-ray escape timescale ($t_0$) that characterizes the late light curve ($>40$ days after peak) and find the effect is modest compared to other possible variations in ejecta structure. We parameterize asymmetry in the $^{56}\mathrm{Ni}$ distribution and calculate $t_0$ for a grid of SN ejecta models spanning a large volume of the asymmetry parameter space. The models have spherical density profiles while the $^{56}\mathrm{Ni}$ distribution in them has various levels of asymmetry. By placing constraints based on the observational measurement of $t_0$ and other general properties of SN Ia ejecta, we find the range of allowed asymmetry in the $^{56}\mathrm{Ni}$ distribution. Considering these constraints we find that some level of asymmetry in the distribution is not ruled out. However, models with a single ejecta mass and varying $^{56}\mathrm{Ni}$ distributions cannot explain the full range of observed $t_0$ values. This strengthens the claim that both Chandrasekhar mass and sub-Chandrasekhar mass explosions are required to explain the diversity of SN Ia observations.

Three-dimensional Simulation of Double Detonations in the Double-degenerate Model for Type Ia Supernovae and Interaction of Ejecta with a Surviving White Dwarf Companion

Abstract We study the hydrodynamics and nucleosynthesis in the double-detonation model of Type Ia supernovae (SNe Ia) and the interaction between the ejecta and a surviving white dwarf (WD) companion in the double-degenerate scenario. We set up a binary star system with 1.0 and 0.6 M ⊙ carbon–oxygen (CO) WDs, where the primary WD consists of a CO core and helium (He) shell with 0.95 and 0.05 M ⊙, respectively. We follow the evolution of the binary star system from the initiation of an He detonation, ignition and propagation of a CO detonation, and the interaction of SN ejecta with the companion WD. The companion (or surviving) WD gets a flung-away velocity of ∼1700 km s−1 and captures 56Ni of ∼0.03 M ⊙ and He of . Such He can be detected on the surface of surviving WDs. The SN ejecta contains a “companion-origin stream” and unburned materials stripped from the companion WD ( ), although the stream compositions would depend on the He shell mass of the companion WD. The ejecta has also a velocity shift of ∼1000 km s−1 due to the binary motion of the exploding primary WD. These features would be prominent in nebular-phase spectra of oxygen emission lines from the unburned materials like SN 2010lp and iPTF14atg and of blue- or redshifted Fe-group emission lines from the velocity shift like a part of subluminous SNe Ia. We expect that SN Ia counterparts to the D6 model would leave these fingerprints for SN Ia observations.

Thermonuclear supernovae and cosmology⋆

Bright and homogeneous, thermonuclear, or type Ia, supernovae (SNeIa) are our best extragalactic distance indicators. Since the 60s, SNeIa have been used as cosmological tools, initially, to estimate the current expansion rate of the Universe, the Hubble constant. Decades ago SNeIa were discovered by chance, in many cases by amateurs. Advances in the instrumentation, techniques and new observational strategies allowed in the 80s to discover SNe in scheduled surveys. Moreover, through calibration relations, a high precision in extragalactic distance determinations was achieved, allowing SNIa observations to reveal the dynamics of the Universe. The Nobel prize in Physics in 2011 was awarded to the leaders of two independent teams “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae”. This is a brief and incomplete story of SNeIa as cosmological tools. In the Madrasah of Granada (Spain), built in 1349 by the Nasrid monarch Yosuf the 1st, Astronomy was one of the disciplines included in the studies. On the Madrasah walls, a calligraphic decoration reads: “make study shine like stars”. It is a good motto for our 4th Azarquiel School of Astronomy.

Bianchi Type-I Dust-Filled Accelerating Brans–Dicke Cosmology

In this paper, spatially homogeneous and anisotropic Bianchi type-I cosmological models of Brans-Dicke theory of gravitation are investigated. The model represents accelerating universe at present and is considered to be dominated by dark energy. Cosmological constant $\Lambda$ is considered as a candidate for the dark energy that has negative pressure and is responsible for the present acceleration. The derived model agrees at par with the recent SN Ia observations. We have set BD-coupling constant $\omega$ to be ~$40000$, ~seeing the solar system tests and evidences. We have discussed the various physical and geometrical properties of the models and have compared them with the corresponding relativistic models.

Progenitors of type Ia supernovae

Natures of progenitors of type Ia Supernovae (SNe Ia) have not yet been clarified. There has been long and intensive discussion on whether the so-called single degenerate (SD) scenario or the double degenerate (DD) scenario, or anything else, could explain a major population of SNe Ia, but the conclusion has not yet been reached. With rapidly increasing observational data and new theoretical ideas, the field of studying the SN Ia progenitors has been quickly developing, and various new insights have been obtained in recent years. This paper aims at providing a summary of the current situation regarding the SN Ia progenitors, both in theory and observations. It seems difficult to explain the emerging diversity seen in observations of SNe Ia by a single population, and we emphasize that it is important to clarify links between different progenitor scenarios and different sub-classes of SNe Ia.

Thermonuclear detonations ensuing white dwarf mergers

The merger of two white dwarfs (WDs) has for many years not been considered as the favoured model for the progenitor system of type Ia supernovae (SNe Ia). But recent years have seen a change of opinion as a number of studies, both observational and theoretical, have concluded that they should contribute significantly to the observed type Ia supernova rate. In this paper, we study the ignition and propagation of detonation through post-merger remnants and we follow the resulting nucleosynthesis up to the point where a homologous expansion is reached. In our study we cover the entire range of WD masses and compositions. For the emergence of a detonation we study three different setups. The first two are guided by the merger remnants from our earlier simulations (Dan et al. 2014}, while for the third one the ignitions were set by placing hotspots with properties determined by spatially resolved calculations taken from the literature. There are some caveats to our approach which we investigate. We carefully compare the nucleosynthetic yields of successful explosions with SN Ia observations. Only three of our models are consistent with all the imposed constraints and potentially lead to a standard type Ia event. The first one, a $0.45\,M_\odot\ {\rm helium\ (He)} + 0.9 \,M_\odot$ carbon-oxygen (CO) WD system produces a sub-luminous, SN 1991bg-like event while the other two, a $0.45\,M_\odot\ {\rm He} + 1.1\,M_\odot$ oxygen-neon (ONe) WD system and a $1.05+1.05\,M_\odot$ system with two CO WDs, are good candidates for common SNe Ia.

TYPE Ia SUPERNOVA PROGENITORS AND CHEMICAL ENRICHMENT IN HYDRODYNAMICAL SIMULATIONS. I. THE SINGLE-DEGENERATE SCENARIO

The nature of the Type Ia supernovae (SNIa) progenitors remains still uncertain. This is a major issue for galaxy evolution models since both chemical and energetic feedback play a major role in the gas dynamics, star formation and therefore in the overall stellar evolution. The progenitor models for the SNIa available in the literature propose different distributions for regulating the explosion times of these events. These functions are known as the Delay Time Distributions (DTDs). This work is the first one in a series of papers aiming at studying five different DTDs for SNIa. Here, we implement and analyse the Single Degenerate scenario (SD) in galaxies dominated by a rapid quenching of the star formation, displaying the majority of the stars concentrated in the bulge component. We find a good fit to both the present observed SNIa rates in spheroidal dominated galaxies, and to the [O/Fe] ratios shown by the bulge of the Milky Way. Additionally, the SD scenario is found to reproduce a correlation between the specific SNIa rate and the specific star formation rate, which closely resembles the observational trend, at variance with previous works. Our results suggest that SNIa observations in galaxies with very low and very high specific star formation rates can help to impose more stringent constraints on the DTDs and therefore on SNIa progenitors.

Robust model comparison disfavors power law cosmology

Late-time power law expansion has been proposed as an alternative to the standard cosmological model and shown to be consistent with some low-redshift data. We test power law expansion against the standard flat $\Lambda$CDM cosmology using goodness-of-fit and model comparison criteria. We consider Type Ia supernova (SN Ia) data from two current compilations (JLA and Union2.1) along with a current set of baryon acoustic oscillation (BAO) measurements that includes the high-redshift Lyman-$\alpha$ forest measurements from BOSS quasars. We find that neither power law expansion nor $\Lambda$CDM is strongly preferred over the other when the SN Ia and BAO data are analyzed separately but that power law expansion is strongly disfavored by the combination. We treat the $R_\text{h} = ct$ cosmology (a constant rate of expansion) separately and find that it is conclusively disfavored by all combinations of data that include SN Ia observations and a poor overall fit when systematic errors in the SN Ia measurements are ignored, despite a recent claim to the contrary. We discuss this claim and some concerns regarding hidden model dependence in the SN Ia data.

Testing vector-tensor gravity with current cosmological observations

A certain vector-tensor theory of gravitation (VT) has been recently applied to cosmology (Phys. Rev. D, 89, 2014, 044035). It leads to encouraging results. The zero order energy density of the vector field accounts for the cosmological constant. It has been recently proved that the VT vector field cannot play the role of the electromagnetic field. The evolution of the scalar perturbations is different in VT and general relativity. Tensor fluctuations evolve in the same way in both theories. Here, the VT evolution equations of the scalar modes are appropriately written, and the initial conditions at high redshift - for numerical integration- are given. The codes COSMOMC and CAMB are modified for applications to VT cosmology and, then, by using the new version of COSMOMC, statistical methods (Markov chains) allow us to fit theoretical VT predictions with current cosmological data obtained in various experiments. Previous encouraging fits were based on WMAP7 data, SN Ia observations, and a minimal model involving seven cosmological parameters. Here a similar preliminary study based on PLANCK data and updated SN Ia observations is presented.

Constraining the double-degenerate scenario for Type Ia supernovae from merger ejected matter

We follow the mass expelled during the WD-WD merger process in a particular case of the Double-Degenerate (DD) scenario for Type Ia supernovae (SNe Ia), and find that the interaction of the SN ejecta with the resulting wind affects the early (first day) light curve in a way that may be in conflict with some SN Ia observations, if the detonation occurs shortly after the merger (i.e., $10^3~{\rm sec} \lesssim t_{\rm exp} \lesssim 1~{\rm day}$). The main source of the expelled mass is a disk-wind, or jets that are launched by the accretion disk around the more massive WD during the viscous phase of the merger. This disk-originated matter (DOM) will be shocked and heated by the SN ejecta from an explosion, leading to additional radiation in the early lightcurve. This enhanced early radiation could then be interpreted as an explosion originating from a progenitor having an inferred radius of one solar radius or more, in conflict with observations of SN 2011fe.

Anisotropic expansion and SNIa: An open issue

We review the appropriateness of using SNIa observations to detect potential signatures of anisotropic expansion in the Universe. We focus on Union2 and SNLS3 SNIa datasets and use the hemispherical comparison method to detect possible anisotropic features. Unlike some previous works where non-diagonal elements of the covariance matrix were neglected, we use the full covariance matrix of the SNIa data, thus obtaining more realistic and not underestimated errors. As a matter of fact, the significance of previously claimed detections of a preferred direction in the Union2 dataset completely disappears once we include the effects of using the full covariance matrix. Moreover, we also find that such a preferred direction is aligned with the orthogonal direction of the SDSS observational plane and this suggests a clear indication that the SDSS subsample of the Union2 dataset introduces a significant bias, making the detected preferred direction unphysical. We thus find that current SNIa surveys are inappropriate to test anisotropic features due to their highly non-homogeneous angular distribution in the sky. In addition, after removal of the highest inhomogeneous sub-samples, the number of SNIa is too low. Finally, we take advantage of the particular distribution of SNLS SNIa sub-sample in the SNLS3 data set, in which the observations were taken along four different directions. We fit each direction independently and find consistent results at the 1σ level. Although the likelihoods peak at relatively different values of Ωm, the low number of data along each direction gives rise to large errors so that the likelihoods are sufficiently broad as to overlap within 1σ.

ΛCDM-type cosmological model and observational constraints

In the present work, we have searched the existence of ΛCDM-type cosmological model in anisotropic Heckmann-Schucking space-time. The matter source that is responsible for the present acceleration of the universe consist of cosmic fluid with p = ω i ρ, where ω i is the equation of state parameter for different cosmic fluids. The Einstein’s field equations have been solved explicitly under some specific choice of parameters that isotropizes the model under consideration. It has been found that the derived model is in good agreement with recent SN Ia observations. Some physical aspects of the model has been discussed in detail.

Accelerating dark energy models with anisotropic fluid in Bianchi type VI0 space-time

Motivated by the increasing evidence for the need of a geometry that resembles Bianchi morphology to explain the observed anisotropy in the WMAP data, we have discussed some features of Bianchi type VIo universes in the presence of a fluid that has an anisotropic equation of state (EoS) parameter in general relativity. We present two accelerating dark energy (DE) models with an anisotropic fluid in Bianchi type VI0 space-time. To ensure a deterministic solution, we choose the scale factor , which yields a time-dependent deceleration parameter, representing a class of models which generate a transition of the universe from the early decelerating phase to the recent accelerating phase. Under suitable conditions, the anisotropic models approach an isotropic scenario. The EoS for DE ω is found to be time-dependent and its existing range for derived models is in good agreement with data from recent observations of type Ia supernovae (SNe Ia) (Knop et al. 2003), SNe Ia data combined with cosmic microwave background (CMB) anisotropy and galaxy clustering statistics (Tegmark et al. 2004a), as well as the latest combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift SNe Ia and galaxy clustering. For different values of n, we can generate a class of physically viable DE models. The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch), which is corroborated by results from recent SN Ia observations. We also observe that our solutions are stable. The physical and geometric aspects of both models are also discussed in detail.