Improving the calibration of Type Ia supernovae using late-time light curves

The use of Type Ia supernovae (SNe Ia) as cosmological standard candles is a key to solving the mystery of dark energy. Improving the calibration of SNe Ia increases their power as cosmological standard candles. We find tentative evidence for a correlation between the late-time light-curve slope and the peak luminosity of SNe Ia in the B band; brighter SNe Ia seem to have shallower light-curve slopes between 100 and 150 d from maximum light. Using a Markov Chain Monte Carlo (MCMC) analysis in calibrating SNe Ia, we are able to simultaneously take into consideration the effect of dust extinction, the luminosity and light-curve width correlation (parametrized by  Δ m ₁₅  ), and the luminosity and late-time light-curve slope correlation. For the available sample of 11 SNe Ia with well-measured late-time light curves, we find that correcting for the correlation between luminosity and late-time light-curve slope of the SNe Ia leads to an intrinsic dispersion of 0.12 mag in the Hubble diagram. Our results have significant implications for future supernova surveys aimed to illuminate the nature of dark energy.     

On the Homogeneity of Type Ia Supernovae Light Curves

A self-similar, hydrodynamic model is derived and used to generate SNe light-curves. It is found that the temporal development of the SN light-curve is governed by a ‘dynamic time’ parameter, and that the observed near-identical, normalized light-curves of Type Ia SNe suggest that they have evolved from progenitor stars of the same central density. Fitting the model parameters to observed Type Ia SNe light-curves suggests that the SNe have originated from the same mass progenitors. The model also provides a theoretical basis for the Phillips observation relating the absolute magnitude of the Type Ia SN to its half-width. This revised version was published online in July 2006 with corrections to the Cover Date.     

The template type Ia supernova 1996X

UBVRIJ photometry and optical spectra of the type Ia SN 1996X obtained at the European Southern Observatory (ESO) during a 1-yr-long observational campaign are presented, and supplemented by late-time Hubble Space Telescope (HST) photometry. Spectroscopically, SN 1996X appears to be a 'normal' SN Ia. The apparent magnitude at maximum was     and the colour     The luminosity decline rate,     is close to average for a SN Ia. The best estimate of the galactic extinction is     and there is evidence that reddening within the parent galaxy is negligible.
Detailed comparison of the light and colour curves of various 'normal' SNe Ia shows that the assumption that multicolour light curves can be described simply as a one-parameter family is not perfect. Together with problems in the calibration of the templates, this may explain the discrepancies in the distance modulus derived adopting different calibrations of the absolute magnitude versus light-curve shape relations. Indeed, we found that M _B ranges from −19.08 to −19.48 and μ ranges from 32.02 to 32.48 depending on the method used.
Computations of model light-curve and synthetic spectra for both early and late times confirm that 1996X is a normal type Ia SN and that a satisfactory fit can be obtained using a W7 progenitor structure only if we adopt the short distance. A larger distance would imply too large a Ni mass for this fainter than average SN Ia.     

Photometric observations of the supernova 2009nr

We present the results of our UBVRI CCD photometry for the second brightest supernova of 2009, SN 2009nr, discovered during a sky survey with the telescopes of the MASTER robotic network. Its light and color curves and bolometric light curves have been constructed. The light-curve parameters and the maximum luminosity have been determined. SN 2009nr is shown to be similar in light-curve shape and maximum luminosity to SN 1991T, which is the prototype of the class of supernovae Ia with an enhanced luminosity. SN 2009nr exploded far from the center of the spiral galaxy UGC 8255 and most likely belongs to its old halo population. We hypothesize that this explosion is a consequence of the merger of white dwarfs.     

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.     

Multidimensional simulations of radiative transfer in Type Ia supernovae

A three-dimensional Monte Carlo code for modelling radiation transport in Type Ia supernovae is described. In addition to tracking Monte Carlo quanta to follow the emission, scattering and deposition of radiative energy, a scheme involving volume-based Monte Carlo estimators is used to allow properties of the emergent radiation field to be extracted for specific viewing angles in a multidimensional structure. This eliminates the need to compute spectra or light curves by angular binning of emergent quanta. The code is applied to two test problems to illustrate consequences of multidimensional structure on the modelling of light curves. First, elliptical models are used to quantify how large-scale asphericity can introduce angular dependence to light curves. Secondly, a model which incorporates complex structural inhomogeneity, as predicted by modern explosion models, is used to investigate how such structure may affect light-curve properties.     

A review of type Ia supernova spectra

SN 2011fe was the nearest and best-observed type Ia supernova in a generation, and brought previous incomplete datasets into sharp contrast with the detailed new data. In retrospect, documenting spectroscopic behaviors of type Ia supernovae has been more often limited by sparse and incomplete temporal sampling than by consequences of signal-to-noise ratios, telluric features, or small sample sizes. As a result, type Ia supernovae have been primarily studied insofar as parameters discretized by relative epochs and incomplete temporal snapshots near maximum light. Here we discuss a necessary next step toward consistently modeling and directly measuring spectroscopic observables of type Ia supernova spectra. In addition, we analyze current spectroscopic data in the parameter space defined by empirical metrics, which will be relevant even after progenitors are observed and detailed models are refined.     

The Rapid X-Ray Variability of V4641 Sagittarii (SAX J1819.3-2525 = XTE J1819-254)

A theoretical light-curve model of the 1985 outburst of RS Ophiuchi based on a thermonuclear runaway model is presented. The system consists of a very massive white dwarf (WD) with an accretion disk and a red giant. The early phase of the V light curve is well reproduced only by the bloated WD photosphere of the thermonuclear runaway model on a 1.35+/-0.01 M middle dot in circle WD, while the later phase is dominated both by the irradiated accretion disk and by the irradiated red giant underfilling the inner critical Roche lobe. The UV light curve is also well reproduced by the same model with a distance of 0.6 kpc to RS Oph. The envelope mass at the optical peak is estimated to be 2x10-6 M( middle dot in circle), indicating a rather high mass accretion rate of 1.2x10-7 M( middle dot in circle) yr(-1) between the 1967 and 1985 outbursts. About 90% of the envelope mass is blown off in the outburst wind, while the residual 10% (2x10-7 M( middle dot in circle)) has been left and added to the helium layer of the WD. The net increasing rate of the WD mass is 1.2x10-8 M( middle dot in circle) yr(-1). Thus, RS Oph is certainly a strong candidate for a Type Ia supernova progenitor.     

Light Curves of the Type II-P Supernova SN 2017eaw: The First 200 Days

We present the results of our UBVRI photometry for the type II-P supernova SN 2017eaw in NGC6946 obtained fromMay 14 to December 7, 2017, at several telescopes, including the 2.5-m telescope at the CaucasusHigh-Altitude Observatory of the SAIMSU. The dates andmagnitudes atmaximumlight and the light-curve parameters have been determined. The color evolution, extinction, and peak luminosity of SN 2017eaw are discussed. The results of our preliminary radiation–gasdynamic simulations of its light curves with the STELLA code describe satisfactorily the UBVRI observational data.     

Constraint on cosmological model with matter creation using complementary astronomical observations

The universe with adiabatic matter creation is considered. It is thought that the negative pressure caused by matter creation can play the role of a dark energy component, and drive the accelerating expansion of the universe. Using the Type Ia supernovae (SNe Ia) data, the observational Hubble parameter data, the Cosmic Microwave Background (CMB) data and the Baryonic Acoustic Oscillation (BAO) data, we make constraints on the cosmological parameters, assuming a spatially flat universe. Our results show that the model with matter creation is consistent with the SNe Ia data, while the joint constraints of all these observational data disfavor this model. If the cosmological constant is taken into account, a traditional model without matter creation is favored by the joint observations.     

A Detectable Candidate for the YORP Effect of Asteroids

The YORP (Yarkovsky-O’Keefe-Radzievskii-Paddack) effect is one of the mechanisms of the long-term dynamical evolution of asteroids. Compared with factors such as collision and gravitational perturbation, the YORP is of small magnitude, and the short-time scale observation effect is inconspicuous, which brings great difficulties to the direct measurement of the YORP. From the Asteroid Lightcurve Database, asteroids having a high confidence rotation period were selected for this study. Two subsample groups for identifying potential asteroids slowed by the YORP effect are provided by using the kernel density estimation method and the Kolmogorov-Smirnov test to analyze the rotation rate distribution characteristics of near-Earth asteroids and main belt asteroids; a screening model is proposed based on the light-curve data of seven YORP asteroids with YORP rotation acceleration, combined with the YORP intensity estimation method and the detection conditions of the YORP effect. Finally, ten candidates that can directly detect the YORP effect through light-curve data in the future are listed based on the screening model.     

小行星YORP效应的可探测候选体

YORP (Yarkovsky-O''Keefe-Radzievskii-Paddack)效应是小行星长期动力学演化的机制之一. 与碰撞、引力摄动等因素相比, YORP效应作用量级小, 短时标观测效应不明显, 这给直接测量YORP效应带来了很大的困难. 利用小行星光变数据库中已知的小行星数据, 统计了小行星的自转速率分布, 使用核密度估计以及Kolmogorov-Smirnov检验分别分析了近地小行星和主带小行星自转速率的分布特性, 分别给出了在近地小行星和主带小行星中寻找受YORP效应影响减速自转的最佳样本群; 基于7颗已被探测到YORP旋转加速度的近地小行星, 利用YORP强度估计方法和光变探测条件建立了筛选模型, 给出了未来可直接通过光变数据探测\lk YORP效应的10颗近地小行星.     

Ia型超新星爆发理论（I）：主要观测特征及其爆发机理

从光谱特性、光变曲线、爆发能量、在星系内分布特征等诸方面,简要介绍了I_a型超新星（SNI_a）的主要观测特征．并根据近年来人们提出的改进标准模型阐述了SNI_a爆发的物理原因和物理过程以及核合成特征．     

On the light variations of Seyfert galaxy 3C120

The fragmentary light-curve of the Seyfert galaxy 3C120, based on photometry of the bestavailable Harvard plates of the past 60 yr, has been subjected to a periodicity analysis using a method (Appendix) particularly suited to this type of irregularly-spaced data. The analysis yields convincing evidence for a period of about 350 d and some indication of a longer period of about 22.5 yr. The observational data often depart appreciably from the light curve synthesized from the two periodic components. In one comparatively well-documented segment (1934–1939), the agreement between observational data and the synthesized model improves if it is assumed that a pair of oppositelydirected phase shifts have occurred, disturbing the 350-day period and then causing it to recover.     

Extinction correction for Type Ia supernova rates – I. The model

In this paper, we present and discuss a new Monte Carlo approach aimed at correcting the observed supernova (SN) rates for the effects of host galaxy dust extinction. The problem is addressed in a general way and the model includes SN position distributions, SN light-curve and spectral library and dust properties and distribution as input ingredients. Even though the recipe we propose is in principle applicable to all SN types, in this paper, we illustrate the use of our model only for Type Ia. These represent, in fact, the simplest test case, basically due to their spectroscopic homogeneity, which to a first approximation allows one to treat them all in the same way. This test case shows that the final results do not depend critically on the spiral arm dust geometry, while the total amount of dust, its properties and the size of the Galactic bulge do have a strong effect. With the availability of more complete spectral libraries and a more accurate knowledge of SN spatial distribution, the method we propose here can be easily extended to core collapse events.     

Multiple regression of GRB luminosity on light-curve properties

Statistical relations between the luminosity L of gamma-ray burster (GRBs) and several of their other observable properties have been discovered. Four of these properties are considered here: the spectral lag; a measure of the light-curve variability; peak energy and the minimum light-curve rise time. Data are taken from a tabulation by Schaefer. Log–log regression of L on various combinations of the four light-curve properties, as well as redshift, is considered, using conventional multiple linear regression, and multiple errors-in-variables regression. Several cases are found in which the regression coefficients of more than one luminosity indicators are significant. In particular, the simultaneous regression of luminosity on peak energy, spectral lag, minimum rise time and redshift is meaningful.     

Evidence for chromatic X-ray light-curve breaks in Swift gamma-ray burst afterglows and their theoretical implications

The power-law decay of the X-ray emission of gamma-ray burst (GRB) afterglows 050319, 050401, 050607, 050713A, 050802 and 050922C exhibits a steepening at about 1–4 h after the burst which, surprisingly, is not accompanied by a break in the optical emission. If it is assumed that both the optical and X-ray afterglows arise from the same outflow then, in the framework of the standard forward shock model, the chromaticity of the X-ray light-curve breaks indicates that they do not arise solely from a mechanism related to the outflow dynamics (e.g. energy injection) or the angular distribution of the blast-wave kinetic energy (structured outflows or jets). The lack of a spectral evolution accompanying the X-ray light-curve break shows that these breaks do not arise from the passage of a spectral break (e.g. the cooling frequency) either. Under these circumstances, the decoupling of the X-ray and optical decays requires that the microphysical parameters for the electron and magnetic energies in the forward shock evolve in time, whether the X-ray afterglow is synchrotron or inverse-Compton emission. For a steady evolution of these parameters with the Lorentz factor of the forward shock and an X-ray light curve arising cessation of energy injection into the blast wave, the optical and X-ray properties of the above six Swift afterglows require a circumburst medium with a r ⁻² radial stratification, as expected for a massive star origin for long GRBs. Alternatively, the chromatic X-ray light-curve breaks may indicate that the optical and X-ray emissions arise from different outflows. Neither feature (evolution of microphysical parameters or the different origin of the optical and X-ray emissions) was clearly required by pre-Swift afterglows.     

The accuracy of light curve interpretation programs revisited

It is stressed that poor convergence criteria are often used in light-curve synthesis programs. A large number of iterations (several tens) is needed to arrive at a definite conclusion about convergence. The result is usually that of some parameters little or no knowledge is gained and that the formal error estimates of all parameters are unrealistically small.     

The effects of parametrization of the dark energy equation of state

We investigate in detail the influence of parametrizations of the dark energy equation of state on reconstructing dark energy geometrical parameters,such as the deceleration parameter q(z) and Om diagnostic.We use a type Ia supernova sample,baryon acoustic oscillation data,cosmic microwave background information along with twelve observational Hubble data points to constrain cosmological parameters.With the joint analysis of these current datasets,we find that the parametrizations of w(z) have little influe...     

Observational constraints on tachyonic chameleon dark energy model

It has been recently shown that tachyonic chameleon model of dark energy in which tachyon scalar field non-minimally coupled to the matter admits stable scaling attractor solution that could give rise to the late-time accelerated expansion of the universe and hence alleviate the coincidence problem. In the present work, we use data from Type Ia supernova (SN Ia) and Baryon Acoustic oscillations to place constraints on the model parameters. In our analysis we consider in general exponential and non-exponential forms for the non-minimal coupling function and tachyonic potential and show that the scenario is compatible with observations.