Properties of SN Ia progenitors from light curves and spectra

With recent advances in theory and observations, direct connections emerge between the progenitors of Type Ia Supernovae (SNe Ia) and the observed light curves and spectra. A direct link is important for our understanding of the supernovae physics, the diversity of SNe Ia and the use of SNe Ia for high-precision cosmology because the details of the explosion depends sensitively on the initial conditions and the explosion scenario(s) realized in nature. Do SNe Ia originate from SD- or DD systems, and do they lead to M_Ch mass explosions or dynamical mergers? Does the statistical distribtion of SNe Ia depend on their environment which can be expected to change with redshift? In this contribution, we will exam from the theoretical point of view the tell-tails for this connection, their consistency with the observations, and future directions. In a first section, we present the physics of the explosion, light curves and spectral formation in a nutshell to help understanding the connection. For details of the progenitor evolution and explosion physics, we refer to reviews and the other contributions in this issue. Each of the topical sections starts with a brief general review followed by a more detailed discussion of specific results. Because the youth of the field, some bias is unavoidable towards results obtained within our collaborations (and FSU). The imprint of the metallicity, progenitor stars and properties such as the central density of the exploding WD are presented. IR spectroscopy, polarimetry and imaging of SNR remnants are discussed as a tool to test for the WD properties, magnetic fields and asymmetries. We discuss different classes of Type Ia supernovae, and their environment. Possible correlations between the spectroscopic and light curve properties of SN Ia are discussed. Finally, the overall emerging picture and future developments are discussed.     

Double Degenerate Stars

Regardless of the formation mechanism, an exotic object, the double degenerate star (DDS), is introduced and investigated, which is composed of baryonic matter and some unknown fermion dark matter. Different from the simple white dwarfs (WDs), there is additional gravitational force provided by the unknown fermion component inside DDSs, which may strongly affect the structure and the stability of such kind of objects. Many possible and strange observational phenomena connecting with them are concisely discussed. Similar to the normal WD, this object can also experience thermonuclear explosion as type Ia supernova explosion when DDS's mass exceeds the maximum mass that can be supported by electron degeneracy pressure. However, since the total mass of baryonic matter can be much lower than that of WD at Chandrasekhar mass limit, the peak luminosity should be much dimmer than what we expect before, which may throw a slight shadow on the standard candle of SN Ia in the research of cosmology.     

No collective neutrino flavor conversions during the supernova accretion phase

We perform a dedicated study of the supernova (SN) neutrino flavor evolution during the accretion phase, using results from recent neutrino radiation hydrodynamics simulations. In contrast to what was expected in the presence of only neutrino-neutrino interactions, we find that the multiangle effects associated with the dense ordinary matter suppress collective oscillations. The matter suppression implies that neutrino oscillations will start outside the neutrino decoupling region and therefore will have a negligible impact on the neutrino heating and the explosion dynamics. Furthermore, the possible detection of the next galactic SN neutrino signal from the accretion phase, based on the usual Mikheyev-Smirnov-Wolfenstein effect in the SN mantle and Earth matter effects, can reveal the neutrino mass hierarchy in the case that the mixing angle θ(13) is not very small.     

Gravitational wave emission from the single-degenerate channel of Type Ia supernovae

The thermonuclear explosion of a C/O white dwarf as a Type Ia supernova (SN Ia) generates a kinetic energy comparable to that released by a massive star during a SN II event. Current observations and theoretical models have established that SNe Ia are asymmetric, and therefore--like SNe II--potential sources of gravitational wave (GW) radiation. We perform the first detailed calculations of the GW emission for a SN Ia of any type within the single-degenerate channel. The gravitationally confined detonation (GCD) mechanism predicts a strongly polarized GW burst in the frequency band around 1 Hz. Third-generation spaceborne GW observatories currently in planning may be able to detect this predicted signal from SNe Ia at distances up to 1 Mpc. If observable, GWs may offer a direct probe into the first few seconds of the SNe Ia detonation.     

Birthrates and delay times of Type Ia supernovae

Type Ia supernovae (SNe Ia) play an important role in diverse areas of astrophysics, from the chemical evolution of galaxies to observational cosmology. However, the nature of the progenitors of SNe Ia is still unclear. In this paper, according to a detailed binary population synthesis study, we obtained SN Ia birthrates and delay times from different progenitor models, and compared them with observations. We find that the Galactic SN Ia birthrate from the double-degenerate (DD) model is close to those infe...     

Constraints on the kinetic energy of type-Ic supernova explosion from young PSR J1906+0746 in a double neutron star candidate

So far among the nineteen pairs of detected double neutron star (DNS) systems, it is a usual fact that the first-born recycled pulsar is detected, however the youngest DNS system PSR J1906+0746, with the characteristic age of 113 kyr, is one of the three detected DNS as a non-recycled and second-born NS, which is believed to be formed by an electron capture or a low energy ultra-stripped iron core-collapse supernova (SN) explosion. The SN remnant around PSR J1906+0746 is too dim to be observed by optical telescopes, then its x-ray flux limit has been given by Chandra. A reference pulsar PSR J1509-5850 with the young characteristic age of 154 kyr was chosen as an object of comparison, which has an SN remnant observed by Chandra and is believed to be formed by iron core SN explosion. We impose a restriction on the maximum kinetic energy of electron-capture (EC) SN explosion that induces the formation of PSR J1906+0746. The estimated result is (4-8)×10⁵⁰ erg (1 erg=10^-7 J), which is consistent with that of the published simulations of the EC process, i.e., a lower value than that of the conventional iron core SN explosion of (1-2)×10⁵¹ erg. As suggested, EC process for NS formation is pertained to the subluminous type Ic SN by the helium star with ONeMg core, thus for the first time we derived the kinetic energy of EC SN explosion of DNS, which may be reconciled with the recent observation of type Ic SN 2014ft with kinetic energy of 2×10⁵⁰ erg.     

Modeling Type Ia supernova explosions

Despite their astrophysical significance-as a major contributor to cosmic nucleosynthesis and as distance indicators in observational cosmology-Type Ia supernovae lack theoretical explanation. Not only is the explosion mechanism complex due to the interaction of (potentially turbulent) hydrodynamics and nuclear reactions, but even the initial conditions for the explosion are unknown. Various progenitor scenarios have been proposed. After summarizing some general aspects of Type Ia supernova modeling, recent simulations of our group are discussed. With a sequence of modeling starting (in some cases) from the progenitor evolution and following the explosion hydrodynamics and nucleosynthesis we connect to the formation of the observables through radiation transport in the ejecta cloud. This allows us to analyze several models and to compare their outcomes with observations. While pure deflagrations of Chandrasekhar-mass white dwarfs and violent mergers of two white dwarfs lead to peculiar events (that may, however, find their correspondence in the observed sample of SNe Ia), only delayed detonations in Chandrasekhar-mass white dwarfs or sub-Chandrasekhar-mass explosions remain promising candidates for explaining normal Type Ia supernovae.     

Magnetized neutron-star mergers and gravitational-wave signals

We investigate the influence of magnetic fields upon the dynamics of, and resulting gravitational waves from, a binary neutron-star merger in full general relativity coupled to ideal magnetohydrodynamics. We consider two merger scenarios: one where the stars have aligned poloidal magnetic fields and one without. Both mergers result in a strongly differentially rotating object. In comparison to the nonmagnetized scenario, the aligned magnetic fields delay the full merger of the stars. During and after merger we observe phenomena driven by the magnetic field, including Kelvin-Helmholtz instabilities in shear layers, winding of the field lines, and transition from poloidal to toroidal magnetic fields. These effects not only mediate the production of electromagnetic radiation, but also can have a strong influence on the gravitational waves. Thus, there are promising prospects for studying such systems with both types of waves.     

超新星研究进展

本文先介绍超新星巡天和分类,简要地论述历史超新星SN 1006一千年,接着讨论核心塌缩超新星物理和具体事例（SN1987A 20年、 SN2006gy、 2008D）及超新星与γ射线暴的联系,文章重点讨论SNIa 和宇宙学,评述了SNIa在宇宙学中的应用和哈勃常数的确定,最后指出超新星研究目前存在的问题。     

Bianchi Type III Anisotropic Dark Energy Models with?Constant Deceleration Parameter

The Bianchi type III dark energy model with constant deceleration parameter is investigated. The equation of state parameter ω is found to be time dependent and its existing range for this model is consistent with the recent observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy clustering statistics. The physical aspects of the dark energy models is discussed.     

大质量恒星的形成:理论与观测

文章简要叙述了有关大质量恒星形成的理论以及相关观测证据。目前大质量恒星形成的理论主要有两种，即吸积说和并合说．吸积说认为，大质量星可能与小质量星形成于相似的过程；并合说主张大质量星可能是由小质量年轻星碰撞合并而成．解决这两种理论争论的关键在于在大质量星附近能否观测到吸积盘的存在，最新的观测表明大质量星更有可能是通过吸积增加自身的质量，但最终解决这一问题可能还需要更多的观测证据。文章还提出了一些本领域尚未解决的问题，为感兴趣的研究者提供参考。     

Exploring the latest Pantheon SN Ia dataset by using three kinds of statistics techniques

In this work, we explore the cosmological consequences of the latest Type Ia supernova (SN Ia)dataset, Pantheon, by adopting the wCDM model. The Pantheon dataset currently contains the largest number of SN Ia samples, which contains 1048 supernovae on the redshift range0 z 2.3. Here we take into account three kinds of SN Ia statistics techniques, including:(1) magnitude statistics (MS), which is the traditional SN Ia statistics technique;(2) flux statistics(FS), which is based on the flux-averaging (FA) method; and (3) improved flux statistics (IFS),which combines the advantages of MS and FS. It should be mentioned that the IFS technique needs to scan the (zcut,Δz) parameters plane, where zcutandΔz are redshift cut-off and redshift interval of FA, respectively. The results are as follows.(1) Using the SN dataset only, the best FA recipe for IFS is (zcut,Δz)=(0.1, 0.08);(2) comparing to the old SN dataset, JLA, adopting the Pantheon dataset can reduce the 2σerror bars of equation of state w by 38%, 47%and 53%for MS, FS and IFS, respectively;(3) FS gives closer results to other observations, such as Baryon acoustic oscillations and cosmic microwave background;(4) compared with FS and IFS,MS more favors a Universe that will end in a ‘big rip’.     

恒星演化和超生爆发理论中某些重要问题的核物理问题

首先,在第1节中我们依次介绍了各种不同质量的恒星演化进程中各个主要热核燃烧的点火条件,致密物质中自由电子系统的简并性对星体热核燃烧的主导作用以及爆炸性核燃烧条件。其次,在第2节中我们讨论了导致恒星核心不稳定坍缩的物理因素和条件。此后,在本第3节中我们评述了Ia型超新星爆发理论尚在急论中的核物理和固体物理的问题。在第4节中我们评述了Ⅱ型（以及Ib型）超新星爆发理论中的严重困难,并且介绍了我们（南京大学研究小组）就超新星中微子延缓爆发机制的关键问题（强大的中微子暴如何产生？）的物理机制提出的具体过程：这中微子暴的强大中微子流量是从刚刚坍缩的高温高密核心通过核物质－－（u,d）夸克系统－－（u,d,s)系统的相变过程在不到1微秒的时间内很快地产生出来的。而且,这个过程导致核心区域的负熵梯度,引起核心区域大规模对流,它将这强大的中微子流量很快地向外输送到中微子球的表面。在第5节中本还介绍了我们就超新星核心高密条件下电荷屏蔽对电子俘获过程的影响所作的探讨研究以及讨论了它对超新星坍缩核心质量（它对超新星瞬时爆发机制成功与否起着关键作用）的可能影响。     

Cosmographic study of the universe’s specific heat: a landscape for cosmology?

Non-abelian gauge field inflation is studied in the context of warm inflation scenario. We introduce this scenario as a mechanism that gives an end for gauge-flation model. Slow-roll parameters and perturbation parameters are presented for this model. We find the general conditions which are required for this model to be realizable in slow-roll approximation. We also develop our model in the context of intermediate and logamediate scenarios which are exact solutions of inflationary field equation in the Einstein theory. General expressions of slow-roll parameters, tensor–scalar ratio and scalar spectral index are presented in terms of inflaton field for these two cases. Our model is compatible with recent observational data from Planck satellite.     

Dark Energy Models with Variable Equation of State Parameter

The dark energy models with variable equation of state parameter ω are investigated by using law of variation of Hubble’s parameter that yields the constant value of deceleration parameter. Here the equation of state parameter ω is found to be time dependent and its existing range for this model is consistent with the recent observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy clustering statistics. The physical significance of the dark energy models have also been discussed.     

On the accelerated expansion of the cosmos

We present a short (and necessarily incomplete) review of the evidence for the accelerated expansion of the Universe. The most direct probe of acceleration relies on the detailed study of supernovae (SN) of type Ia. Assuming that these are standardizable candles and that they fairly sample a homogeneous and isotropic Universe, the evidence for acceleration can be tested in a model-independent and calibration-independent way. Various light-curve fitting procedures have been proposed and tested. While several fitters give consistent results for the so-called Constitution set, they lead to inconsistent results for the recently released SDSS SN. Adopting the SALT fitter and relying on the Union set, cosmic acceleration is detected by a purely kinematic test at 7σ when spatial flatness is assumed and at 4σ without any assumption on the spatial geometry. A weak point of the described method is the local set of SN (at z<0.2), as these SN are essential to anchor the Hubble diagram. These SN are drawn from a volume much smaller than the Hubble volume and could be affected by local structure. Without the assumption of homogeneity, there is no evidence for acceleration, as the effects of acceleration are degenerate with the effects of inhomogeneities. Unless we sit in the centre of the Universe, such inhomogeneities can be constrained by SN observations by means of tests of the isotropy of the Hubble flow.     

Black hole binaries and microquasars

This is a general review Oil the observations and physics of black hole X-ray binaries and microquasars, with the emphasize on recent developments in the high energy regime. The focus is put on understanding the accretion flows and measuring the parameters of black holes in them. It includes mainly two parts： i） Brief review of several recent review article on this subject; ii） Further development on several topics, including black hole spin measurements, hot accretion flows, corona formation, state transitions and thermal stability of standard think disk. This is thus not a regular bottom-up approach, which I feel not necessary at this stage. Major effort is made in making and incorporating from many sources useful plots and illustrations, in order to make this article more comprehensible to non-expert readers. In the end I attempt to make a unification scheme on the accretion-outflow （wind/jet） connections of all types of aecreting BHs of all accretion rates and all BH mass scales, and finally provide a brief outlook.     

May a supernova bang twice?

The Mont Blanc group reports a burst of neutrinos in the LSD detector occuring the day before the optical discovery of SN1987A. The Kamiokande (K2) and IMB experiments see neutrino bursts ∼4 h 43 min after LSD. The K2 observations at LSD time here said to contradict LSD. I argue that the K2 results strongly support the LSD pulse(!). I critically analyse the data, and prove that all experiments are compatible at all times. I discuss the plausibility and predictive power of a two-neutrino-burst scenario, wherein the progenitor's core first became a neutron star, and subsequently recollapsed into a black hole (or strange star) as matter left behind by a partially failed shock wave accreted on and around the neutron star, with a calculated fall-back time of a few hours     

Towards an understanding of Type Ia supernovae from a synthesis of theory and observations

Motivated by the fact that calibrated light curves of Type Ia supernovae (SNe Ia) have become a major tool to determine the expansion history of the Universe, considerable attention has been given to, both, observations and models of these events over the past 15 years. Here, we summarize new observational constraints, address recent progress in modeling Type Ia supernovae by means of three-dimensional hydrodynamic simulations, and discuss several of the still open questions. It will be be shown that the new models have considerable predictive power which allows us to study observable properties such as light curves and spectra without adjustable non-physical parameters. This is a necessary requisite to improve our understanding of the explosion mechanism and to settle the question of the applicability of SNe Ia as distance indicators for cosmology. We explore the capabilities of the models by comparing them with observations and we show how such models can be applied to study the origin of the diversity of SNe Ia.     

60Fe anomaly in a deep-sea manganese crust and implications for a nearby supernova source

A nearby supernova (SN) explosion in the past can be confirmed by the detection of radioisotopes on Earth that were produced and ejected by the SN. We have now measured a well resolved time profile of the 60Fe concentration in a deep-sea ferromanganese crust and found a highly significant increase 2.8 Myr ago. The amount of 60Fe is compatible with the deposition of ejecta from a SN at a distance of a few 10 pc. The well defined time of the SN explosion makes it possible to search for plausible correlations with other events in Earth's history.