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Type Ia Supernovae (SNe Ia) are believed to be thermonuclear explosions of a white dwarf. They can be used as mature cosmological standardized candles, leading to the discovery of the accelerating expansion of the Universe. However, the explosion mechanism has not yet been fully clarified. In this paper, we first present nucleosynthetic features of a leading explosion scenario, namely a delayed-detonation scenario. Based on this, we propose a new and strong observational constraint on the explosion mechanism through emission lines from neutron-rich Fe-peaks. Especially, we show that an asymmetry in the explosion is likely a generic feature. We further argue that the diversity arising from various viewing angles can be an origin of observational diversities of SNe Ia seen in their spectral features (suspected possible biases in cosmology) and colors (related to the extinction estimate in cosmology). Using these new insights could open up a possibility of using SNe Ia as more precise distance indicators than currently employed. [ABSTRACT FROM AUTHOR]

The nature of Type Ia supernova (SN Ia) explosions has not yet been clarified, despite their importance in astrophysics and cosmology. Recent theoretical investigations suggest that asymmetric distribution of initial thermonuclear sparks may be a key in the SN Ia explosion mechanism. In this paper, the first observational evidence of the asymmetry in SN Ia explosions is presented: We have found that late-time nebular spectra of various SNe Ia show a diversity in wavelengths of emission lines. This feature is inconsistent with any spherically symmetric explosion models, and indicates that the innermost region, a likely product of the deflagration wave propagation, shows an off-set with respect to the explosion center. The diversity in the emission-line wavelengths could naturally be explained by a combination of different viewing angles. [ABSTRACT FROM AUTHOR]

The calculations for the evolution of dust within Population III supernova remnants (SNRs) are presented, based on the models of dust formed in the unmixed ejecta of Type II SNe. We show that once dust grains collide with the reverse shock penetrating into the ejecta, their fates strongly depend on the initial radius aini. For SNRs expanding into the interstellar medium (ISM) with nH,0 = 1 cm-3, grains of aini<0.05 μm are trapped in the hot gas to be completely destroyed; grains of aini = 0.05–0.2 μm are piled up in the dense shell formed behind the forward shock; grains of aini>0.2 μm are injected into the ISM without being eroded significantly. The total mass of surviving dust is 0.01 to 0.8 M⊙ for nH,0 = 10 to 0.1 cm-3. We also investigate the influence of the piled-up dust on the elemental abundances of the second-generation stars formed in the dense shell of Population III SNRs. The comparison of the calculated elemental abundances with those observed in hyper-metal-poor (HMP) and ultra-metal-poor (UMP) stars indicates that the transport of dust separated from metal-rich gas can be an important process in determining the abundance patterns of Mg and Si in HMP and UMP stars. [ABSTRACT FROM AUTHOR]

Features in nucleosynthesis and emission processes in jet-like aspherical hypernova explosions are presented. The aspherical model yields large (Co, Zn)/Fe and small (Mn, Cr)/Fe as are consistent with abundance patterns in metal-poor halo stars, indicating important contribution of hypernovae in the early Galactic chemical evolution. The same model also yields large amount of 44Ti. As for emission features, this model is found to reproduce successfully the optical light curve and spectra of hypernova SN 1998bw. The viewing angle is close to the polar direction. The same model explains a peculiar [OI] 6300Å profile observed in SN 2003jd, only if the viewing angle is different from that for SN 1998bw. These analyses support the validity of the aspherical models, therefore the use of the models as a reference model for hypernova nucleosynthesis. In addition, theoretical prediction is presented for high energy emissions from the decays of56Ni and56Co. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We review the characteristics of nucleosynthesis and radioactivities in 'hypernovae', i.e., supernovae with very large explosion energies (&gsim; 10[SUP52] ergs) and their γ-ray line signatures. We also discuss the [SUP44]Ti line γ-rays from SN1987A and the detectability with INTEGRAL. Signatures of hypernova nucleosynthesis are seen in the large [(Ti, Zn)/Fe] ratios in very metal poor stars. Radioactivities in hypernovae compared to those of ordinary core-collapse supernovae show the following characteristics: 1) The complete Si burning region is more extended, so that the ejected mass of [SUP56]Ni can be much higher. 2) Si-burning takes place in higher entropy and more α-rich environment. Thus the [SUP44]Ti abundance relative to [SUP56]Ni is much larger. In aspherical explosions, [SUP44]Ti is even more abundant and ejected with velocities as high as ~ 15,000 km s[SUP-1], which could be observed in γ-ray line profiles. 3) The abundance of [SUP26]Al is not so sensitive to the explosion energy, while the [SUP60]Fe abundance is enhanced by a factor of ~ 3. [ABSTRACT FROM AUTHOR]

We describe the evolution of dust within Population III supernova remnants (SNRs) and investigate the chemical compositions of the dust piled up in their dense shells. We show that the resulting abundance patterns of the major elements in the dense shells are in good agreement with that observed for a Galactic halo star, SDSS J102915+172927. This allows us to propose that SDSS J102915+172927 might be the second-generation star formed in the dust-enriched dense shell of a Population III SNR. We conclude that the segregation of dust from the metal-rich ejecta gas can be an important process in determining the abundance patterns of primitive low-mass stars. [ABSTRACT FROM AUTHOR]

Type Ic supernova SN 1998bw is a prototype of a supernova (SN) associated with a Gamma-Ray Burst (GRB). In this paper, we present similarities and differences in SN 1998bw and other SNe Ib/c. SN 1998bw is shown to be a highly bipolar explosion viewed from the polar direction, based on comparisons between multi-dimensional radiation transfer calculations and various optical observations. The explosion energy is estimated to be ∼10 times that of normal SNe Ib/c, even if the viewing angle effect on the estimate of the energy is taken into account. The typical explosion geometry of other SNe Ib/c are derived based on late-time spectra taken by the SUBARU and VLT telescopes. They are shown to be in general asymmetric as well, likely sharing the similar bipolar geometry. The degree of the asymmetry is shown to be on average smaller in normal SNe Ib/c than in SN 1998bw, indicating the intrinsically different explosion mechanisms. [ABSTRACT FROM AUTHOR]

A long GRB is thought to occur when a massive star ends its life and thus it is expected to be accompanied by a type Ic supernova (SN) which also results from a massive star. Several nearby long GRBs are observed with type Ic SNe. However, some nearby long GRBs are observed without SNe, even though they are close enough to be able to observe the accompanied SNe (e.g., GRB060614). Within our current picture of long GRBs, long GRBs should be accompanied by SNe and these long GRBs without SNe are one of the challenges for the current theory of long GRBs. One possible reason is that the accompanied SNe were so faint that we just missed them. For example, SN 2008ha was only as bright as ∼-14 mag in the R band at maximum brightness. The explosion energy, ejecta mass, and 56Ni mass of SN 2008ha are estimated as about 1048 erg, 0.1 M⊙, and 0.003 M⊙, respectively. If such a SN is accompanied by long GRBs, we might miss it. We performed numerical calculations of hydrodynamics and radiation transport and confirmed that SN 2008ha could have been a type Ic supernova and originated from a core-collapse SN with a significant amount of fallback. This demonstrates that some type Ic SNe like SN 2008ha could be very faint because of fallback. Our results suggest that long GRBs without SNe could have been accompanied by such faint SNe with fallback and we could have just missed the accompanied SNe and the current picture of long GRBs would be consistent with long GRBs without SNe. [ABSTRACT FROM AUTHOR]

The explosion mechanism of supernovae (SNe) is a longstanding mystery. Clarifying the multi-dimensional shape of the explosion by observations will give important constraints on the explosion mechanism. Among various kinds of observations, polarization measurement is the most direct method to study the geometry of a SN, an extragalactic point source. We have been conducting spectropolarimetric observations of stripped-envelope SNe with the Subaru telescope. We have detected linear polarization at various lines, undoubtedly indicating that the explosion is not spherically symmetric. We discuss possible explosion geometry to explain these features. [ABSTRACT FROM AUTHOR]

We calculate evolution, collapse, explosion, and nucleosynthesis of Population III very massive stars with 500M⊙ and 1000M⊙. It was found that both 500M⊙ and 1000M⊙ models enter the region of pair-instability but continue to undergo core collapse to black holes. For moderately aspherical explosions, the patterns of nucleosynthesis match the observational data of intergalactic and intercluster medium and hot gases in M82, better than models involving hypernovae and pair instability supernovae. Our results suggest that explosions of Population III core-collapse very massive stars contribute significantly to the chemical evolution of gases in clusters of galaxies. The final black hole masses are about 500M⊙ for our most massive 1000M⊙ models. This result may support the view that Population III very massive stars are responsible for the origin of intermediate mass black holes which were recently reported to be discovered. [ABSTRACT FROM AUTHOR]