scholarly journals Probing the isotropy of cosmic acceleration using different supernova samples

2019 ◽  
Vol 79 (9) ◽  
Author(s):  
Z. Q. Sun ◽  
F. Y. Wang
Keyword(s):  
Cosmic Acceleration ◽  
Type Ia Supernovae ◽  
Data Sets ◽  
Data Set ◽  
Cosmic Expansion ◽  
Fitting Method ◽  
Comparison Results ◽  
Type Ia ◽  
Ia Supernovae ◽  
Fitting Parameters

Abstract Recent studies indicated that an anisotropic cosmic expansion may exist. In this paper, we use three data sets of type Ia supernovae (SNe Ia) to probe the isotropy of cosmic acceleration. For the Union2.1 data set, the direction and magnitude of the dipole are $$(l=309.3^{\circ } {}^{+ 15.5^{\circ }}_{-15.7^{\circ }} ,\ b = -8.9^{\circ } {}^{ + 11.2^{\circ }}_{-9.8^{\circ }} )$$(l=309.3∘-15.7∘+15.5∘,b=-8.9∘-9.8∘+11.2∘), and $$\ A=(1.46 \pm 0.56) \times 10^{-3}$$A=(1.46±0.56)×10-3 from dipole fitting method. The hemisphere comparison results are $$\delta =0.20,l=352^{\circ },b=-9^{\circ }$$δ=0.20,l=352∘,b=-9∘. For the Constitution data set, the results are $$(l=67.0^{\circ }{}^{+ 66.5^{\circ }}_{-66.2^{\circ }},\ b=-0.6^{\circ }{}^{+ 25.2^{\circ }}_{-26.3^{\circ }})$$(l=67.0∘-66.2∘+66.5∘,b=-0.6∘-26.3∘+25.2∘), and $$\ A=(4.4 \pm 5.0) \times 10^{-4}$$A=(4.4±5.0)×10-4 for dipole fitting and $$\delta = 0.56,l=141^{\circ },b=-11^{\circ }$$δ=0.56,l=141∘,b=-11∘ for hemisphere comparison. For the JLA data set, no significant dipolar or quadrupolar deviation is found. We find previous works using (l, b, A) directly as fitting parameters may get improper results. We also explore the effects of anisotropic distributions of coordinates and redshifts on the results using Monte-Carlo simulations. We find that the anisotropic distribution of coordinates can cause dipole directions and make dipole magnitude larger. Anisotropic distribution of redshifts is found to have no significant effect on dipole fitting results.

scholarly journals Study of some parameters of modified Chaplygin gas in Galileon gravity theory from observational perspective

2014 ◽  
Vol 92 (12) ◽  
pp. 1667-1675 ◽  
Author(s):  
Chayan Ranjit ◽  
Prabir Rudra ◽  
Ujjal Debnath
Keyword(s):  
Chaplygin Gas ◽  
Cosmic Acceleration ◽  
Joint Analysis ◽  
Type Ia Supernovae ◽  
Distance Modulus ◽  
Modified Chaplygin Gas ◽  
Data Set ◽  
Type Ia ◽  
Ia Supernovae ◽  
Best Fit

We have assumed the Friedmann–Robertson–Walker model of the universe in Galileon gravity, which is filled with dark matter and modified Chaplygin gas (MCG) type dark energy. We present the Hubble parameter in terms of some unknown parameters and observational parameters with the redshift z. Some cosmological parameters are reconstructed and plots are generated to study the nature of the model and its viability. It is seen that the model is perfectly consistent with the present cosmic acceleration. From observed Hubble data (OHD) set or Stern data set of 12 points, we have obtained the bounds of the arbitrary parameters (A, B) and (A, C) by minimizing the χ2 test. Next because of joint analysis of OHD + baryonic acoustic oscillation (BAO) and OHD+BAO+CMB observations, we have also obtained the best fit values and the bounds of the parameters (A, B) and (A, C) by fixing some other parameters. The best-fit values and bounds of the parameters are obtained with 66%, 90%, and 99% confidence levels for OHD, OHD+BAO, and OHD+BAO+CMB joint analysis. Next we have also taken type Ia supernovae data set (union2 data set with 557 data points). The distance modulus μ(z) against redshift z for our theoretical MCG model in Galileon gravity have been tested for the best fit values of the parameters and the observed type Ia supernovae union2 data sample and from this, we have concluded that our model is in agreement with the union2 sample data.

scholarly journals Gauging the cosmic acceleration with recent type Ia supernovae data sets

2018 ◽  
Vol 97 (8) ◽  
Author(s):  
Hermano Velten ◽  
Syrios Gomes ◽  
Vinicius C. Busti
Keyword(s):  
Cosmic Acceleration ◽  
Type Ia Supernovae ◽  
Data Sets ◽  
Type Ia ◽  
Ia Supernovae

scholarly journals ParSNIP: Generative Models of Transient Light Curves with Physics-enabled Deep Learning

2021 ◽  
Vol 162 (6) ◽  
pp. 275
Author(s):  
Kyle Boone
Keyword(s):  
Three Dimensional ◽  
Generative Models ◽  
Light Curves ◽  
Type Ia Supernovae ◽  
Data Sets ◽  
Data Set ◽  
Out Of Sample ◽  
Type Ia ◽  
Ia Supernovae

Abstract We present a novel method to produce empirical generative models of all kinds of astronomical transients from data sets of unlabeled light curves. Our hybrid model, which we call ParSNIP, uses a neural network to model the unknown intrinsic diversity of different transients and an explicit physics-based model of how light from the transient propagates through the universe and is observed. The ParSNIP model predicts the time-varying spectra of transients despite only being trained on photometric observations. With a three-dimensional intrinsic model, we are able to fit out-of-sample multiband light curves of many different kinds of transients with model uncertainties of 0.04–0.06 mag. The representation learned by the ParSNIP model is invariant to redshift, so it can be used to perform photometric classification of transients even with heavily biased training sets. Our classification techniques significantly outperform state-of-the-art methods on both simulated (PLAsTiCC) and real (PS1) data sets with 2.3× and 2× less contamination, respectively, for classification of Type Ia supernovae. We demonstrate how our model can identify previously unobserved kinds of transients and produce a sample that is 90% pure. The ParSNIP model can also estimate distances to Type Ia supernovae in the PS1 data set with an rms of 0.150 ± 0.007 mag compared to 0.155 ± 0.008 mag for the SALT2 model on the same sample. We discuss how our model could be used to produce distance estimates for supernova cosmology without the need for explicit classification.

scholarly journals Windowing artefacts likely account for recent claimed detection of oscillating cosmic scale factor

2020 ◽  
Vol 498 (4) ◽  
pp. 5512-5516
Author(s):  
Sasha R Brownsberger ◽  
Christopher W Stubbs ◽  
Daniel M Scolnic
Keyword(s):  
Type Ia Supernovae ◽  
Data Sets ◽  
Analysis Method ◽  
Data Set ◽  
Statistical Fluctuations ◽  
Data Analyses ◽  
Type Ia ◽  
History Of ◽  
Ia Supernovae ◽  
The Universe

ABSTRACT Using the Pantheon data set of Type Ia supernovae, a recent publication (R20 in this work) reports a  2σ detection of oscillations in the expansion history of the Universe. The study conducted by R20 is wholly worthwhile. However, we demonstrate that there is a $\gt 10{{\ \rm per\ cent}}$ chance of statistical fluctuations in the Pantheon data producing a false oscillatory signal larger than the oscillatory signal that R20 report. Their results are a less than 2σ detection. Applying the R20 methodology to simulated Pantheon data, we determine that these oscillations could arise due to analysis artefacts. The uneven spacing of Type Ia supernovae in redshift space and the complicated analysis method of R20 impose a structured throughput function. When analysed with the R20 prescription, about $11{{\ \rm per\ cent}}$ of artificial ΛCDM data sets produce a stronger oscillatory signal than the actual Pantheon data. Our results underscore the importance of understanding the false ‘signals’ that can be introduced by complicated data analyses.

scholarly journals Model-independent cosmic acceleration and redshift-dependent intrinsic luminosity in type-Ia supernovae

2019 ◽  
Vol 625 ◽  
pp. A15 ◽  
Author(s):  
I. Tutusaus ◽  
B. Lamine ◽  
A. Blanchard
Keyword(s):  
Spline Interpolation ◽  
High Redshift ◽  
Cosmic Acceleration ◽  
Expansion Rate ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Model Independent ◽  
Ia Supernovae ◽  
The Universe ◽  
Intrinsic Luminosity

Context. The cosmological concordance model (ΛCDM) is the current standard model in cosmology thanks to its ability to reproduce the observations. The first observational evidence for this model appeared roughly 20 years ago from the type-Ia supernovae (SNIa) Hubble diagram from two different groups. However, there has been some debate in the literature concerning the statistical treatment of SNIa, and their stature as proof of cosmic acceleration. Aims. In this paper we relax the standard assumption that SNIa intrinsic luminosity is independent of redshift, and examine whether it may have an impact on our cosmological knowledge and more precisely on the accelerated nature of the expansion of the universe. Methods. To maximise the scope of this study, we do not specify a given cosmological model, but we reconstruct the expansion rate of the universe through a cubic spline interpolation fitting the observations of the different cosmological probes: SNIa, baryon acoustic oscillations (BAO), and the high-redshift information from the cosmic microwave background (CMB). Results. We show that when SNIa intrinsic luminosity is not allowed to vary as a function of redshift, cosmic acceleration is definitely proven in a model-independent approach. However, allowing for redshift dependence, a nonaccelerated reconstruction of the expansion rate is able to fit, at the same level of ΛCDM, the combination of SNIa and BAO data, both treating the BAO standard ruler rd as a free parameter (not entering on the physics governing the BAO), and adding the recently published prior from CMB observations. We further extend the analysis by including the CMB data. In this case we also consider a third way to combine the different probes by explicitly computing rd from the physics of the early universe, and we show that a nonaccelerated reconstruction is able to nicely fit this combination of low- and high-redshift data. We also check that this reconstruction is compatible with the latest measurements of the growth rate of matter perturbations. We finally show that the value of the Hubble constant (H0) predicted by this reconstruction is in tension with model-independent measurements. Conclusions. We present a model-independent reconstruction of a nonaccelerated expansion rate of the universe that is able to fit all the main background cosmological probes nicely. However, the predicted value of H0 is in tension with recent direct measurements. Our analysis points out that a final reliable and consensual value for H0 is critical to definitively prove cosmic acceleration in a model-independent way.

scholarly journals Monte Carlo radiative transfer for the nebular phase of Type Ia supernovae

2019 ◽  
Vol 492 (2) ◽  
pp. 2029-2043 ◽  
Author(s):  
L J Shingles ◽  
S A Sim ◽  
M Kromer ◽  
K Maguire ◽  
M Bulla ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Atomic Data ◽  
Type Ia Supernovae ◽  
Data Set ◽  
High Ionization ◽  
Type Ia ◽  
Non Local ◽  
Ionization Balance ◽  
Ia Supernovae ◽  
Modest Effect

ABSTRACT We extend the range of validity of the artis 3D radiative transfer code up to hundreds of days after explosion, when Type Ia supernovae (SNe Ia) are in their nebular phase. To achieve this, we add a non-local thermodynamic equilibrium population and ionization solver, a new multifrequency radiation field model, and a new atomic data set with forbidden transitions. We treat collisions with non-thermal leptons resulting from nuclear decays to account for their contribution to excitation, ionization, and heating. We validate our method with a variety of tests including comparing our synthetic nebular spectra for the well-known one-dimensional W7 model with the results of other studies. As an illustrative application of the code, we present synthetic nebular spectra for the detonation of a sub-Chandrasekhar white dwarf (WD) in which the possible effects of gravitational settling of 22Ne prior to explosion have been explored. Specifically, we compare synthetic nebular spectra for a 1.06 M⊙ WD model obtained when 5.5 Gyr of very efficient settling is assumed to a similar model without settling. We find that this degree of 22Ne settling has only a modest effect on the resulting nebular spectra due to increased 58Ni abundance. Due to the high ionization in sub-Chandrasekhar models, the nebular [Ni ii] emission remains negligible, while the [Ni iii] line strengths are increased and the overall ionization balance is slightly lowered in the model with 22Ne settling. In common with previous studies of sub-Chandrasekhar models at nebular epochs, these models overproduce [Fe iii] emission relative to [Fe ii] in comparison to observations of normal SNe Ia.

scholarly journals VARIABLE CHAPLYGIN GAS: CONSTRAINTS FROM CMBR ANDSNe Ia

2006 ◽  
Vol 15 (07) ◽  
pp. 1089-1098 ◽  
Author(s):  
GEETANJALI SETHI ◽  
SUSHIL K. SINGH ◽  
PRANAV KUMAR ◽  
DEEPAK JAIN ◽  
ABHA DEV
Keyword(s):  
Equation Of State ◽  
Positive Function ◽  
Chaplygin Gas ◽  
Scale Factor ◽  
Type Ia Supernovae ◽  
Data Set ◽  
Cosmological Scale ◽  
Type Ia ◽  
Ia Supernovae

We constrain the parameters of the variable Chaplygin gas model, using the location of peaks of the CMBR spectrum and the SNe Ia "gold" data set. The equation of state of the model is P = -A(a)/ρ, where A(a) = A0a-nis a positive function of the cosmological scale factor a, A0and n> being constants. The variable Chaplygin gas interpolates from the dust-dominated era to the quintessence dominated era. The model is found to be compatible with current type Ia supernovae data and the location of the first peak if the values of Ωmand n lie in the interval [0.017, 0.117] and [-1.3, 2.6], respectively.

scholarly journals Lick Observatory Supernova Search follow-up program: photometry data release of 93 Type Ia supernovae

2019 ◽  
Vol 490 (3) ◽  
pp. 3882-3907 ◽  
Author(s):  
Benjamin E Stahl ◽  
WeiKang Zheng ◽  
Thomas de Jaeger ◽  
Alexei V Filippenko ◽  
Andrew Bigley ◽  
...  
Keyword(s):  
Light Curves ◽  
Type Ia Supernovae ◽  
Data Set ◽  
Future Studies ◽  
Processing Pipeline ◽  
Type Ia ◽  
Template Fitting ◽  
Ia Supernovae ◽  
Distance Indicators

ABSTRACT We present BVRI and unfiltered light curves of 93 Type Ia supernovae (SNe Ia) from the Lick Observatory Supernova Search (LOSS) follow-up program conducted between 2005 and 2018. Our sample consists of 78 spectroscopically normal SNe Ia, with the remainder divided between distinct subclasses (3 SN 1991bg-like, 3 SN 1991T-like, 4 SNe Iax, 2 peculiar, and 3 super-Chandrasekhar events), and has a median redshift of 0.0192. The SNe in our sample have a median coverage of 16 photometric epochs at a cadence of 5.4 d, and the median first observed epoch is ∼4.6 d before maximum B-band light. We describe how the SNe in our sample are discovered, observed, and processed, and we compare the results from our newly developed automated photometry pipeline to those from the previous processing pipeline used by LOSS. After investigating potential biases, we derive a final systematic uncertainty of 0.03 mag in BVRI for our data set. We perform an analysis of our light curves with particular focus on using template fitting to measure the parameters that are useful in standardizing SNe Ia as distance indicators. All of the data are available to the community, and we encourage future studies to incorporate our light curves in their analyses.

The value of the Hubble–Lemaître constant queried by Type Ia supernovae: a journey from the Calán-Tololo Project to the Carnegie Supernova Program

2020 ◽  
Vol 500 (1) ◽  
pp. 1095-1113
Author(s):  
Mario Hamuy ◽  
Régis Cartier ◽  
Carlos Contreras ◽  
Nicholas B Suntzeff
Keyword(s):  
Binary Stars ◽  
Direct Consequence ◽  
Systematic Difference ◽  
Type Ia Supernovae ◽  
Data Sets ◽  
Type Ia ◽  
Metadata Analysis ◽  
Nearby Galaxies ◽  
Ia Supernovae

ABSTRACT We assess the robustness of the two highest rungs of the ‘cosmic distance ladder’ for Type Ia supernovae and the determination of the Hubble–Lemaître constant. In this analysis, we hold fixed Rung 1 as the distance to the LMC determined to 1 per cent using detached eclipsing binary stars. For Rung 2, we analyse two methods, the TRGB and Cepheid distances for the luminosity calibration of Type Ia supernovae in nearby galaxies. For Rung 3, we analyse various modern digital supernova samples in the Hubble flow, such as the Calán-Tololo, CfA, CSP, and Supercal data sets. This metadata analysis demonstrates that the TRGB calibration yields smaller H0 values than the Cepheid calibration, a direct consequence of the systematic difference in the distance moduli calibrated from these two methods. Selecting the three most independent possible methodologies/bandpasses (B, V, J), we obtain H0 = 69.9 ± 0.8 and H0= 73.5 ± 0.7 $\, \rm km\, s^{-1} \, Mpc^{-1}$from the TRGB and Cepheid calibrations, respectively. Adding in quadrature the systematic uncertainty in the TRGB and Cepheid methods of 1.1 and 1.0 $\, \rm km\, s^{-1} \, Mpc^{-1}$, respectively, this subset reveals a significant 2.0σ systematic difference in the calibration of Rung 2. If Rung 1 and Rung 2 are held fixed, the different formalisms developed for standardizing the supernova peak magnitudes yield consistent results, with a standard deviation of 1.5 $\, \rm km\, s^{-1} \, Mpc^{-1}$, that is, Type Ia supernovae are able to anchor Rung 3 with 2 per cent precision. This study demonstrates that Type Ia supernovae have provided a remarkably robust calibration of R3 for over 25 yr.

scholarly journals Optical Spectroscopy of Type Ia Supernovae

2005 ◽  
Vol 192 ◽  
pp. 161-165
Author(s):  
Thomas Matheson
Keyword(s):  
Spectroscopic Data ◽  
Comprehensive Analysis ◽  
Light Curves ◽  
Type Ia Supernovae ◽  
Data Set ◽  
Type Ia ◽  
Spectroscopic Database ◽  
Similarities And Differences ◽  
Ia Supernovae ◽  
Homogeneous Data

SummaryThe supernova (SN) group at the Harvard-Smithsonian Center for Astrophysics has been using the facilities of the F. L. Whipple Observatory to gather optical photometric and spectroscopic data on nearby supernovae for several years. The collection of spectra of Type Ia SNe is now large enough to allow a comprehensive analysis. I will present preliminary results from a study of a subsample of the CfA Type Ia spectroscopic database, with over 200 spectra of 31 Type Ia SNe. The SNe selected all have well-calibrated light curves and cover a wide scope of luminosity classes. The epochs of observation range from fourteen days before maximum to fifty days past maximum. All of the spectra were obtained with the same instrument on the same telescope, and were reduced using the same techniques. With such a large, homogeneous data set, the spectroscopic similarities and differences among Type Ia SNe become readily apparent.

Sign in / Sign up

Export Citation Format

Share Document