Showing papers on "Hypernova published in 2008"

The metamorphosis of supernova SN 2008D/XRF 080109: a link between supernovae and GRBs/hypernovae.

Abstract: The only supernovae (SNe) to show gamma-ray bursts (GRBs) or early x-ray emission thus far are overenergetic, broad-lined type Ic SNe (hypernovae, HNe). Recently, SN 2008D has shown several unusual features: (i) weak x-ray flash (XRF), (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SN Ic HNe, and (iv) development of helium lines as in SNe Ib. Detailed analysis shows that SN 2008D was not a normal supernova: Its explosion energy (E approximately 6x10(51) erg) and ejected mass [ approximately 7 times the mass of the Sun (M(middle dot in circle))] are intermediate between normal SNe Ibc and HNe. We conclude that SN 2008D was originally a approximately 30 M(middle dot in circle) star. When it collapsed, a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse to black holes.

Tycho Brahe's 1572 supernova as a standard type Ia as revealed by its light-echo spectrum.

Abstract: Type Ia supernovae, used as distance indicators by cosmologists, result from thermonuclear explosions of white dwarf stars in binary systems. Important questions remain about how the explosions proceed and the nature of the progenitors. A nearby example would be a help in finding the answers; now we have one. The recent discovery of light echoing from Tycho Brahe's supernova of 1572, and now the determination of its optical spectrum, confirm the suspicion that 'SN 1572' is in fact a type Ia supernova in our cosmological backyard, the Milky Way. This puts stringent constraints on explosion models that can now be compared in detail to observations of both the explosion 436 years ago and the remnant as we see it today. This study reports an optical spectrum of Tycho Brahe's supernova near maximum brightness, obtained from a scattered-light echo more than four centuries after the direct light of the explosion swept past Earth. It is found that SN 1572 belongs to the majority class of normal type Ia supernovae. Type Ia supernovae are thermonuclear explosions of white dwarf stars in close binary systems1. They play an important role as cosmological distance indicators and have led to the discovery of the accelerated expansion of the Universe2,3. Among the most important unsolved questions4 about supernovae are how the explosion actually proceeds and whether accretion occurs from a companion or by the merging of two white dwarfs. Tycho Brahe’s supernova of 1572 (SN 1572) is thought to be one of the best candidates for a type Ia supernova in the Milky Way5. The proximity of the SN 1572 remnant has allowed detailed studies, such as the possible identification of the binary companion6, and provides a unique opportunity to test theories of the explosion mechanism and the nature of the progenitor. The determination of the hitherto unknown7,8,9 spectroscopic type of this supernova is crucial in relating these results to the diverse population of type Ia supernovae10. Here we report an optical spectrum of Tycho’s supernova near maximum brightness, obtained from a scattered-light echo more than four centuries after the direct light from the explosion swept past the Earth. We find that SN 1572 belongs to the majority class of normal type Ia supernovae.

The Destruction of Cosmological Minihalos by Primordial Supernovae

Abstract: We present numerical simulations of primordial supernovae in cosmological minihalos at z ~ 20. We consider Type II supernovae, hypernovae, and pair instability supernovae (PISN) in halos from 6.9 × 105 to 1.2 × 107 M☉, those in which Population III stars are expected to form via H2 cooling. Our simulations are the first to follow the evolution of the blast from a free expansion on spatial scales of 10−4 pc until its approach to pressure equilibrium in the relic H II region of the progenitor, ~1000 pc. Supernovae in H II regions first expand adiabatically and then radiate strongly upon collision with baryons ejected from the halo during its photoevaporation by the progenitor. In contrast to previous findings, supernovae in neutral halos promptly emit most of their kinetic energy as X-rays, but retain enough momentum to seriously disrupt the halo. Explosions in H II regions escape into the IGM, but neutral halos confine the blast and its metals. In H II regions, a prompt second generation of stars may form in the remnant at radii of 100-200 pc. Explosions confined by massive halos instead recollapse, with infall rates in excess of 10−2 M☉ yr−1 that heavily contaminate their interior. This fallback may either fuel massive black hole growth at very high redshifts or create the first globular clusters with radii of 10-20 pc at the center of the halo. Our findings suggest that the first primitive galaxies may therefore have formed sooner, with greater numbers of stars and distinct chemical signatures, than in current models.

The Proto-Neutron Star Phase of the Collapsar Model and the Route to Long-Soft Gamma-Ray Bursts and Hypernovae

Abstract: Recent stellar evolutionary calculations of massive low-metallicity fast-rotating main-sequence stars yield iron cores at collapse that are endowed with high angular momentum. It is thought that high angular momentum and black hole formation are critical ingredients for the collapsar model of long-soft γ-ray bursts (GRBs). We present two-dimensional multigroup, flux-limited-diffusion MHD simulations of the collapse, bounce, and immediate postbounce phases of a 35 M☉ collapsar-candidate model of Woosley & Heger. Provided that the magnetorotational instability (MRI) operates in the differentially rotating surface layers of the millisecond-period neutron star, we find that a magnetically driven explosion occurs during the proto-neutron star phase, in the form of a baryon-loaded nonrelativistic jet, and that a black hole, which is central to the collapsar model, does not form. Paradoxically, although much uncertainty surrounds stellar mass loss, angular momentum transport, magnetic fields, and the MRI, current models of chemically homogeneous evolution at low metallicity yield massive stars with iron cores that may have too much angular momentum to avoid a magnetically driven, hypernova-like explosion in the immediate postbounce phase. We surmise that fast rotation in the iron core may inhibit, rather than enable, collapsar formation, which requires a large angular momentum above the core but not in it. Variations in the angular momentum distribution of massive stars at core collapse might explain both the diversity of Type Ic supernovae/hypernovae and their possible association with a GRB. A corollary might be that, through its effect on magnetic field amplification, the angular momentum distribution, rather than the progenitor mass, is the distinguishing characteristic of these outcomes.

The Extended HST Supernova Survey: The Rate of SNe Ia at z > 1.4 Remains Low

Abstract: We use the HST ACS imaging of the two GOODS fields during Cycles 11, 12, and 13 to derive the Type Ia supernova rate in four redshift intervals in the range -->0.2 . The sample now consists of 56 Type Ia supernovae. The rates we derive are consistent with our results based on the Cycle 11 observations. In particular, the small number of supernovae detected at -->z > 1.4 supports our previous result that there is a drop in the Type Ia supernova rate at high redshift, suggesting a long time delay between the formation of the progenitor star and the explosion of the supernova. If described by a simple one-parameter model, we find a characteristic delay time of 2-3 Gyr. However, a number of recent results based on, e.g., low-redshift supernova samples and supernova host galaxy properties suggest that the supernova delay-time distribution is bimodal. In this model a major fraction of the Type Ia supernova rate are prompt and follow the star formation rate, while a smaller fraction of the rate have a long delay time, making this channel proportional to mass. While our results are fully consistent with the bimodal model at low redshifts, the low rate we find at -->z > 1.4 appears to contradict these results. Models that correct for star formation hidden by dust may explain at least part of the differences. Here we discuss this possibility together with other ways to reconcile data and models.

THE END OF AMNESIA : A NEW METHOD FOR MEASURING THE METALLICITY OF TYPE Ia SUPERNOVA PROGENITORS USING MANGANESE LINES IN SUPERNOVA REMNANTS

Abstract: We propose a new method to measure the metallicity of Type Ia supernova progenitors using Mn and Cr lines in the X-ray spectra of young supernova remnants. We show that the Mn-to-Cr mass ratio in Type Ia supernova ejecta is tightly correlated with the initial metallicity of the progenitor, as determined by the neutron excess of the white dwarf material before thermonuclear runaway. We use this correlation, together with the flux of the Cr and Mn Kα X-ray lines in the Tycho supernova remnant recently detected by Suzaku, to derive a metallicity of log (Z) = − 1.32+ 0.67−0.33 for the progenitor of this supernova, which corresponds to log (Z/Z☉) = 0.60+ 0.31−0.60 according to the latest determination of the solar metallicity by Asplund and coworkers. The uncertainty in the measurement is large, but metallicities much smaller than the solar value can be confidently discarded. We discuss the implications of this result for future research on Type Ia supernova progenitors.

On the Origin and Survival of Ultra-High-Energy Cosmic-Ray Nuclei in Gamma-Ray Bursts and Hypernovae

Abstract: The chemical composition of the ultra-high-energy (UHE) cosmic rays serves as an important clue to their origin. Recent measurements of the elongation rates by the Pierre Auger Observatory hint at the possible presence of heavy or intermediate-mass nuclei in the UHE cosmic rays. Gamma-ray bursts (GRBs) and hypernovae have been suggested as possible sources of the UHE cosmic rays. Here we derive constraints on the physical conditions under which UHE heavy nuclei, if they are accelerated in these sources, can survive in their intense photon fields. We find that in the GRB external shock and hypernova scenarios, UHE nuclei can easily survive photodisintegration. In the GRB internal shock scenario, UHE nuclei can also survive, provided the dissipation radius and/or the bulk Lorentz factor of the relativistic outflow are relatively large, or if the low-energy self-absorption break in the photon spectrum of the prompt emission occurs above several keV. In internal shocks and in the other scenarios, intermediate-mass UHE nuclei have a higher probability of survival against photodisintegration than UHE heavy nuclei such as Fe.

Nucleosynthesis in Magnetically Driven Jets from Collapsars

Abstract: We have made detailed calculations of the composition of magnetically driven jets ejected from collapsars, or rapidly rotating massive stars, based on long-term magnetohydrodynamic simulations of their core collapse with various distributions of magnetic field and angular momentum before collapse. We follow the evolution of the abundances of about 4000 nuclides from the collapse phase to the ejection phase and through the jet generation phase using a large nuclear reaction network. We find that the r-process successfully operates only in energetic jets (>1051 ergs), such that U and Th are synthesized abundantly, even when the collapsar has a relatively weak magnetic field (1010 G) and a moderately rotating core before the collapse. The abundance patterns inside the jets are similar to those of the r-elements in the solar system. About 0.01-0.06 M☉ of neutron-rich, heavy nuclei are ejected from a collapsar with energetic jets. The higher energy jets have larger amounts of 56Ni, varying from 3.7 × 10−4 to 0.06 M☉. Less energetic jets, which eject small amounts of 56Ni, could induce a gamma-ray burst (GRB) without a supernova, such as GRB 060505 or GRB 060614. Considerable amounts of r-elements are likely to be ejected from GRBs with hypernovae, if both the GRB and hypernova are induced by jets that are driven near the black hole.

HD 271791: An Extreme Supernova Runaway B Star Escaping from the Galaxy

Abstract: Hyper-velocity stars (HVSs) were first predicted by theory to be the result of the tidal disruption of a binary system by a super-massive black hole (SMBH) that accelerates one component to beyond the Galactic escape velocity (the Hills mechanism). Because the Galactic centre hosts such a SMBH it is the suggested place of origin for HVSs. However, the SMBH paradigm has been challenged recently by the young HVS HD271791 because its kinematics point to a birthplace in the metal-poor rim of the Galactic disc. Here we report the atmosphere of HD271791 to indeed show a sub-solar iron abundance along with an enhancement of the alpha-elements, indicating capture of nucleosynthesis products from a supernova or a more energetic hypernova. This implies that HD271791 is the surviving secondary of a massive binary system disrupted in a supernova explosion. No such run-away star has ever been found to exceed the Galactic escape velocity, hence HD271791 is the first hyper-runaway star. Such a run-away scenario is an alternative to the Hills mechanism for the acceleration of some HVSs with moderate velocities. The observed chemical composition of HD271791 puts invaluable observational constraints on nucleosynthesis in a supernova from the core-collapse of a very massive star (M_ZAMS >= 55 M_Sun), which may be observed as a gamma-ray burst of the long-duration/soft-spectrum type.

HD 271791: an extreme supernova runaway B star escaping from the galaxy

Abstract: Hypervelocity stars (HVSs) were first predicted by theory to be the result of the tidal disruption of a binary system by a supermassive black hole (SMBH) that accelerates one component to beyond the Galactic escape velocity (the Hills mechanism). Because the Galactic center hosts such a SMBH it is the suggested place of origin for HVSs. However, the SMBH paradigm has been challenged recently by the young HVS HD 271791 because its kinematics point to a birthplace in the metal-poor rim of the Galactic disk. Here we report the atmosphere of HD 271791 to indeed show a subsolar iron abundance along with an enhancement of the α-elements, indicating capture of nucleosynthesis products from a supernova or a more energetic hypernova. This implies that HD 271791 is the surviving secondary of a massive binary system disrupted in a supernova explosion. No such runaway star has ever been found to exceed the Galactic escape velocity; hence HD 271791 is the first hyperrunaway star. Such a runaway scenario is an alternative to the Hills mechanism for the acceleration of some HVSs with moderate velocities. The observed chemical composition of HD 271791 puts invaluable observational constraints on nucleosynthesis in a supernova from the core collapse of a very massive star (MZAMS 55 M☉), which may be observed as a gamma-ray burst of the long-duration/soft-spectrum type.

The most massive core collapse supernova progenitors

Abstract: The discovery of the extremely luminous supernova SN 2006gy, possibly interpreted as a pair instability supernova, renewed the interest in very massive stars. We explore the evolution of these objects, which end their life as pair instability supernovae or as core-collapse supernovae with relatively massive iron cores, up to about 3 M?.

Possible signature of hypernova nucleosynthesis in a beryllium-rich halo dwarf

Abstract: As part of a large survey of halo and thick disc stars, we found one halo star, HD 106038, exceptionally overabundant in beryllium. In spite of its low metallicity, [Fe/H]=−1.26, the star has log(Be/H) =−10.60, which is similar to the solar meteoritic abundance, log(Be/H) =−10.58. This abundance is more than 10 times higher the abundance of stars with similar metallicity and cannot be explained by models of chemical evolution of the Galaxy that include the standard theory of cosmic ray spallation. No other halo star exhibiting such a beryllium overabundance is known. In addition, overabundances of Li, Si, Ni, Y and Ba are also observed. We suggest that all these chemical peculiarities, excepting the Ba abundance, can be simultaneously explained if the star was formed in the vicinity of a hypernova.

Ultraluminous X‐ray Sources: Beambags and Optical Counterparts

Abstract: A significant fraction of ultraluminous X‐ray sources appear to be embedded in observable ionized nebulae that take the form of large, several 100 pc diameter interstellar bubbles. Here we review optical observations of these bubbles, their importance for our understanding of the nature of ULXs, the energetics involved and their formation and evolution. Among the results obtained are new arguments against conventional superbubble scenarios and hypernova remnants, and we present the case in favour of ULX‐wind/jet driven bubbles. We report the discovery of new ULXs in very large SNR candidates in nearby galaxies, and finally present an image of a triple X‐ray source coincident with the radio‐bright bubble S26 in the galaxy NGC 7793 which appears to be a clone of the microquasar SS433/W50 system.

LMC X-3 May Be a Relic of a GRB Similar to Cosmological GRBs

Abstract: The present scenario for high-luminosity long gamma-ray bursts is strongly influenced by the paper of Fruchter and coworkers. Whereas the main contention of this paper that these GRBs occur in low-metallicity irregular galaxies is based on a considerable collection of observational results and although the main thesis is doubtless correct, the paper does not explain the dynamics that produces such GRBs and much of the discussion not directly concerning the main thesis is incorrect. We propose a dynamics and elucidate how the Fruchter et al. results may be tested, in our neighborhood in the LMC, suggesting that LMC X-3 is a relic of a high-luminosity explosion, probably accompanied by a GRB and hypernova explosion. The way to test our suggestion is to measure the system velocity of the present black hole. We correct errors of the Fruchter et al. paper in stellar evolution, so that the study of GRBs is consistent with it. We show that the subluminous GRB 060218 had a low-mass black hole as central engine.

Ultraluminous X-ray Sources: Beambags and Optical Counterparts

Abstract: A significant fraction of ultraluminous X-ray sources appear to be embedded in observable ionized nebulae that take the form of large, several 100 pc diameter interstellar bubbles. Here we review optical observations of these bubbles, their importance for our understanding of the nature of ULXs, the energetics involved and their formation and evolution. Among the results obtained are new arguments against conventional superbubble scenarios and hypernova remnants, and we present the case in favour of ULX-wind/jet driven bubbles. We report the discovery of new ULXs in very large SNR candidates in nearby galaxies, and finally present an image of a triple X-ray source coincident with the radio-bright bubble S26 in the galaxy NGC 7793 which appears to be a clone of the microquasar SS433/W50 system.

Simulations of Cosmic Chemical Enrichment

Abstract: We simulate cosmic chemical enrichment with a hydrodynamical model including supernova and hypernova feedback. We find that the majority of stars in present-day massive galaxies formed in much smaller galaxies at high redshifts, despite their late assembly times. The hypernova feedback drives galactic outflows efficiently in low mass galaxies, and these winds eject heavy elements into the intergalactic medium. The ejected baryon fraction is larger for less massive galaxies, correlates well with stellar metallicity. The observed mass-metallicity relation is well reproduced as a result of the mass-dependent galactic winds.

LMC X-3 May Be a Relic of a GRB Similar to Cosmological GRBs

Abstract: The present scenario for high-luminosity long gamma-ray bursts is strongly influenced by the paper of Fruchter et al. (2006). Whereas the main contention of this paper that these GRBs occur in low-metallicity irregular galaxies is based on a considerable collection of observational results and although the main thesis is doubtless correct, the paper does not explain the dynamics that produces such GRBs and much of the discussion not directly concerning the main thesis is wrong. We propose a dynamics and elucidate how the Fruchter et al. (2006) results may be tested, in our neighborhood in the LMC, suggesting that LMC X-3 is a relic of a high luminosity explosion, probably accompanied by a GRB and hypernova explosion. The way to test our suggestion is to measure the system velocity of the present black hole. We correct errors of the Fruchter et al. paper in stellar evolution, so that the study of GRBs is consistent with it. We show that the subluminous GRB 060218 had a low-mass black hole as central engine.

Secondary Photons from High-Energy Protons Accelerated in Hypernovae

Abstract: Recent observations show that hypernovae may deposit some fraction of their kinetic energy in mildly relativistic ejecta. In the dissipation process of such ejecta in a stellar wind, cosmic-ray protons can be accelerated up to ~1019 eV. We discuss the TeV to MeV gamma-ray and the X-ray photon signatures of cosmic rays accelerated in hypernovae. Secondary X-ray photons, emitted by electron-positron pairs produced via cascade processes due to high-energy protons, are the most promising targets for X-ray telescopes. Synchrotron photons emitted by protons can appear in the GeV band, requiring nearby (<40 Mpc) hypernovae for detection with GLAST. In addition, air Cerenkov telescopes may be able to detect regenerated TeV photons emitted by electron-positron pairs generated by CMB attenuation of π0-decay photons.

The Destruction of Cosmological Minihalos by Primordial Supernovae

Abstract: We present numerical simulations of primordial supernovae in cosmological minihalos at $z \sim$ 20. We consider Type II supernovae, hypernovae, and pair instability supernovae (PISN) in halos from 6.9 $\times$ 10$^5$ - 1.2 $\times$ 10$^7$ $\Ms$, those in which Population III stars are expected to form via H$_2$ cooling. The supernovae evolve along two evolutionary paths according to whether they explode in \ion{H}{2} regions or neutral halos. Those in \ion{H}{2} regions first expand adiabatically and then radiate strongly upon collision with baryons ejected from the halo during its photoevaporation by the progenitor. Explosions in neutral halos promptly emit most of their kinetic energy as x-rays, but retain enough momentum to seriously disrupt the halo. We find that the least energetic of the supernovae are capable of destroying halos $\lesssim$ 10$^7$ $\Ms$, while a single PISN can destroy even more massive halos. Blasts in \ion{H}{2} regions disperse heavy elements into the IGM, but neutral halos confine the explosion and its metals. In \ion{H}{2} regions, a prompt second generation of stars may form in the remnant at radii of 100 - 200 pc in the halo. Explosions confined by large halos instead recollapse, with infall rates in excess of 10$^{-2}$ $\Ms$ yr$^{-1}$ that heavily contaminate their interior. This fallback may either fuel massive black hole growth at very high redshifts or create the first globular cluster with a radius of 10 - 20 pc at the center of the halo. Our findings allow the possibility that the first primitive galaxies formed sooner, with greater numbers of stars and distinct chemical abundance patterns, than in current models.

Cosmic ray protons in the energy range 1016–1018.5 eV: stochastic gyroresonant acceleration in hypernova shocks?

Abstract: The hypernovae (HNe) associated with gamma-ray bursts (GRBs) may have a fairly steep energy-velocity distribution, i.e. E(>=beta) proportional to beta(-q) for q = beta(o), where beta is the velocity of the material and beta(o) similar to 0.1 is the velocity of the slowest ejecta of the HN explosion, both in units of the speed of light (c). The cosmic ray protons above the second knee but below the ankle may be accelerated by the HN shocks in the velocity range of beta similar to beta(o)-4 beta(o). When beta <= 4 beta(o), the radius of the shock front to the central engine is very large and the medium decelerating the HN outflow is very likely to be homogeneous. With this argument, we show that for q similar to 1.7, as inferred from the optical modelling of SN 2003lw, the stochastic gyroresonant acceleration model can account for the spectrum change of high-energy protons around the second knee. The self-magnetized shock acceleration model, however, yields too steep a spectrum which is inconsistent with the observation unless the medium surrounding the HN is a free wind holding up to a radius similar to 1-10 kpc.

Type Ib Supernova 2008D associated with the Luminous X-ray Transient 080109: An Energetic Explosion of a Massive Helium Star

Abstract: We present a theoretical model for supernova (SN) 2008D associated with the luminous X-ray transient 080109. The bolometric light curve and optical spectra of the SN are modelled based on the progenitor models and the explosion models obtained from hydrodynamic/nucleosynthetic calculations. We find that SN 2008D is a more energetic explosion than normal core-collapse supernovae, with an ejecta mass of Mej = 5.3 +- 1.0 Msun and a kinetic energy of E = 6.0 +- 2.5 x 10^{51} erg. The progenitor star of the SN has a 6-8 Msun He core with essentially no H envelope (< 5 x 10^{-4} Msun) prior to the explosion. The main-sequence mass of the progenitor is estimated to be Mms =20-25 Msun, with additional systematic uncertainties due to convection, mass loss, rotation, and binary effects. These properties are intermediate between those of normal SNe and hypernovae associated with gamma-ray bursts. The mass of the central remnant is estimated as 1.6 - 1.8 Msun, which is near the boundary between neutron star and black hole formation.

Central engines of Gamma Ray Bursts. Magnetic mechanism in the collapsar model

Abstract: In this study we explore the magnetic mechanism of hypernovae and relativistic jets of long duration gamma ray bursts within the collapsar scenario. This is an extension of our earlier work[1]. We track the collapse of massive rotating stars onto a rotating central black hole using axisymmetric general relativistic magnetohydrodynamic code that utilizes a realistic equation of state and takes into account the cooling associated with emission of neutrinos and the energy losses due to dissociation of nuclei. The neutrino heating is not included. We describe solutions with different black hole rotation, mass accretion rate, and strength of progenitor’s magnetic field. Some of them exhibits strong explosions driven by Poynting‐dominated jets with power up to 12×1051 erg s. These jets originate from the black hole and powered via the Blandford‐Znajek mechanism. A provisional criterion for explosion is derived. A number of simulation movies can be downloaded from http://www.maths.leeds.ac.uk/serguei/research/mo...

Abundances of Sr, Y, and Zr in Metal-Poor Stars and Implications for Chemical Evolution in the Early Galaxy

Abstract: Studies of nucleosynthesis in neutrino-driven winds from nascent neutron stars show that the elements from Sr through Ag with mass numbers A~88-110 are produced by charged-particle reactions (CPR) during the alpha-process in the winds. Accordingly, we have attributed all these elements in stars of low metallicities ([Fe/H] -0.32 for all metal-poor stars. The high-resolution data now available on Sr abundances in Galactic halo stars show that there is a great shortfall of Sr relative to Fe in many stars with [Fe/H]<-3. This is in direct conflict with the above prediction. The same conflict also exists for two other CPR elements Y and Zr. The very low abundances of Sr, Y, and Zr observed in stars with [Fe/H]<-3 thus require a stellar source that cannot be low-mass or normal SNe. We show that this observation requires a stellar source leaving behind black holes and that hypernovae (HNe) from progenitors of ~25-50M_sun are the most plausible candidates. (Abridged)

Chemodynamical simulations of the Milky Way Galaxy

Abstract: We simulate the chemodynamical evolution of the Milky Way Galaxy, including the nucleosynthesis yields of hypernovae and a new progenitor model for Type Ia Supernovae (SNe Ia). In our nucleosynthesis yields of core-collapse supernovae, we use light curve and spectral fitting to individual supernovae to estimate the mass of the progenitor, the explosion energy, and the iron mass produced. A large contribution of hypernovae is required from the observed abundance of Zn ([Zn/Fe] ~0). In our progenitor model of SNe Ia, based on the single degenerate scenario, the SN Ia lifetime distribution spans a range of 0.1–20 Gyr with peaks at both ~ 0.1 and 1 Gyr. A metallicity effect from white dwarf winds is required from the observed trends of elemental abundance ratios (i.e., [(α,Mn,Zn)/Fe]-[Fe/H] relations). In our simulated Milky Way-type galaxy, the kinematical and chemical properties of the bulge, disk, and halo are broadly consistent with observations. 80% of the thick disk stars are older than ~8 Gyr and tend to have larger [α/Fe] than in the thin disk.

Chemical Yields from Supernovae and Hypernovae

Abstract: We review the final stages of stellar evolution, supernova properties, and chemical yields as a function of the progenitor's mass. (1) 8 - 10 M⊙ stars are super-AGB stars when the O+Ne+Mg core collapses due to electron capture. These AGB-supernovae may constitute an SN 2008S-like sub-class of Type IIn supernovae. These stars produce little α-elements and Fe-peak elements, but are important sources of Zn and light p-nuclei. (2) 10 - 90 M⊙ stars undergo Fe-core collapse. Nucleosynthesis in aspherical explosions is important, as it can well reproduce the abundance patterns observed in extremely metal-poor stars. (3) 90 - 140 M⊙ stars undergo pulsational nuclear instabilities at various nuclear burning stages, including O and Si-burning. (4) Very massive stars with M ≳ 140 M⊙ either become pair-instability SNe, or undergo core-collapse to form intermediate mass black holes if the mass loss is small enough.

Ultraluminous X-ray Sources and Their Nebulae

Abstract: One of the interesting features of Ultraluminous X‐ray sources is that many of them are surrounded by luminous nebulae exhibiting diverse observational properties. In different cases the nebulae are photoionized or shock‐powered. Generally, the two energy sources appear to coexist. ULX bubble nebulae may be considered a new class of shock‐powered nebulae similar to upscaled versions of stellar wind bubbles. Their expansion rates support constant energy influx rather than single powerful events like Hypernova explosions.

Broadband Radiation from Primary Electrons in Very Energetic Supernovae

Abstract: A class of very energetic supernovae (hypernovae) is associated with long gamma-ray bursts, in particular with a less energetic but more frequent population of gamma-ray bursts. Hypernovae also appear to be associated with mildly relativistic jets or outflows, even in the absence of gamma-ray bursts. Here we consider radiation from charged particles accelerated in such mildly relativistic outflows with kinetic energies of ~10^(50) ergs. The radiation processes of the primarily accelerated electrons considered are synchrotron radiation and inverse Compton scattering of synchrotron photons (synchrotron self-Compton; SSC) and of supernova photons (external inverse Compton; EIC). In the soft X-ray regime, both the SSC and EIC flux can be the dominant component, but due to their very different spectral shapes, it should be easy to distinguish between them. When the fraction of the kinetic energy going into the electrons (ee) is large, the SSC is expected to be important; otherwise, the EIC will dominate. The EIC flux is quite high, almost independently of ee, providing a good target for X-ray telescopes such as XMM-Newton and Chandra. In the GeV gamma-ray regime, the EIC would be the dominant radiation process and the Gamma-Ray Large Area Space Telescope (GLAST, which has been renamed the Fermi Gamma-ray Space Telesope) should be able to probe the value of ee, the spectrum of the electrons, and their maximum acceleration energy. Accelerated protons also lead to photon radiation through the secondary electrons produced by the photopion and photopair processes. We find that over a significant range of parameters the proton component is generally less prominent than the primary electron component. We discuss the prospects for the detection of the X-ray and GeV signatures of the mildly relativistic outflow of hypernovae.

Gamma-ray bursts as VHE-UHE sources

Abstract: Gamma-ray bursts are capable of accelerating cosmic rays up to GZK energies Ep ~ 1020 eV, which can lead to a flux at Earth comparable to that observed by large EAS arrays such as Auger. The semi-relativistic outflows inferred in GRB-related hypernovae are also likely sources of somewhat lower energy cosmic rays. Leptonic processes, such as synchrotron and inverse Compton, as well as hadronic processes, can lead to GeV-TeV gamma-rays measurable by GLAST, AGILE, or ACTs, providing useful probes of the burst physics and model parameters. Photo-meson interactions also produce neutrinos at energies ranging from sub-TeV to EeV, which will be probed with forthcoming experiments such as IceCube, ANITA and KM3NeT. This would provide information about the fundamental interaction physics, the acceleration mechanism, the nature of the sources and their environment.

Cataclysmic Cosmic Events and How to Observe Them

Abstract: Cataclysmic Variables.- Novae and Recurrent Novae.- Solar Flares, Giant Prominences, and Flare Stars.- Bright Supernovae and Hypernovae.- Active Galaxies.- Gamma Ray Bursters.- How to Do Visual and CCD Photometry.