Many radioactive nuclei relevant for gamma-ray astrophysics are synthesized during explosive events, such as classical novae and supernovae. A review of recent results of explosive nucleosynthesis in these scenarios is presented, with a special emphasis on the ensuing gamma-ray emission from individual nova and supernova explosions. The influence of the dynamic properties of the ejecta on the gamma-ray emission features, as well as the still remaining uncertainties in nova and supernova models is also reviewed.
Explosive nucleosynthesis is a combination of the nuclear physics of thermonuclear reactions, and the hydrodynamics of the plasma in which the reactions occur. It depends upon the initial conditions---the stellar evolution up to the explosive instability, and the nature of the explosion mechanism. Some key issues for explosive nucleosynthesis are the interaction of burning with hydrodynamics, the degree of microscopic mixing in convective zones, and the breaking of spherical symmetry by convection and rotation. Recent experiments on high intensity lasers provides new opportunities for laborato…
We study the few body reactions in explosive nucleosynthesis of light-to-heavy mass elements in various astrophysical conditions. In neutrino-driven winds of gravitational core collapse of SNeII, several light nuclei as well as heavy unstable nuclei paly significant roles in producing r-process elements. We discuss how the three-body reaction $^4$He$(αn, γ)^9$Be, whose cross section is poorly known, plays very critical role. We make note that several other reactions in the r-process are relevant to a Big-Bang nucleosynthesis. We discuss briefly a Galactic chemical evolution.
We have performed 1-dimensional calculations for explosive nucleosynthesis in collapse-driven supernova and investigated its sensitivity to the initial form of the shock wave. We have found the tendency that the peak temperature becomes higher around the mass cut if the input energy is injected more in the form of kinetic energy rather than internal energy. Then, the mass cut becomes larger, and, as a result, neutron-rich matter is less included in the ejecta; this is favorable for producing the observational data compared with a previous model. Our results imply that the standard method to tr…
In recent years the technique of Adaptive Mesh Refinement (AMR) has been successfully applied to several astrophysical problems. This method should also allow a consistent multi-dimensional modelling of supernova explosions. In this contribution we address some of the computational difficulties encountered when trying to apply the AMR method to explosive nucleosynthesis and supernova envelope ejection.
There have been attempts to fit the abundance patterns of extremely metal-poor stars with supernova nucleosynthesis models for the lighter elements than Zn. On the other hand, observations have revealed that the presence of EMP stars with peculiarly high ratio of "weak r-process elements" Sr, Y and Zr. Although several possible processes were suggested for the origin of these elements, the complete solution for reproducing those ratios is not found yet. In order to reproduce the abundance patterns of such stars, we investigate a model with neutron rich matter ejection from the inner region of …
We present the \nuk{Al}{26} and \nuk{Fe}{60} yields produced by a generation of solar metallicity stars ranging in mass between 11 and 120\msun. We discuss the production sites of these $γ$ ray emitters and quantify the relative contributions of the various components. More specifically we provide the separate contribution of the wind, the C convective shell and the explosive Ne/C burning to the total \nuk{Al}{26} yield per each stellar model in our grid. We provide the contributions of the He convective shell, the C convective shell and the explosive Ne/C burning to the \nuk{Fe}{60} yield as …
Aspherical explosion models for the hypernova (hyper-energetic supernova) SN 1998bw are presented. Nucleosynthesis in aspherical explosions is examined with a two-dimensional hydrodynamical code and a detailed nuclear reaction network. Aspherical explosions lead to a strong $α$-rich freezeout, thus enhancing the abundance ratios [$^{44}$Ca, $^{48}$Ti, and $^{64}$Zn / Fe] in the ejecta. The nebular line profiles of the Fe-dominated blend near 5200 Åand of [\OI] 6300,6363 Åare calculated and compared with the observed late time spectra of SN 1998bw. Compared with the spherical model, the unusual…
We perform 2-dimensional relativistic hydrodynamical simulations in the context of collapsar model. Calculations of explosive nucleosynthesis are also accomplished. We investigate the influence of the structure of the progenitor and energy deposition rate on the resulting explosive nucleosynthesis, assuming that 56Ni is mainly synthesized in the jet launched by the neutrino heating. We show the amount of 56Ni is very sensitive to the energy deposition rate. Thus we conclude that it is quite natural not to detect an underlying supernova in some X-ray afterglows as in GRB 010921. We also point o…
The collapsar engine behind long-duration gamma-ray bursts extracts the energy released from the rapid accretion of a collapsing star onto a stellar-massed black hole. In a collapsing star, this black hole can form in two ways: the direct collapse of the stellar core into a black hole and the delayed collapse of a black hole caused by fallback in a weak supernova explosion. In the case of a delayed-collapse black hole, the strong collapsar-driven explosion overtakes the weak supernova explosion before shock breakout, and it is very difficult to distinguish this black hole formation scenario fr…
Two-dimensional hydrodynamic simulations are performed to investigate explosive nucleosynthesis in a collapsar using the model of MacFadyen and Woosley (1999). It is shown that 56Ni is not produced in the jet of the collapsar sufficiently to explain the observed amount of a hypernova when the duration of the explosion is \sim 10 sec, which is considered to be the typical timescale of explosion in the collapsar model. Even though a considerable amount of 56Ni is synthesized if all explosion energy is deposited initially, the opening angles of the jets become too wide to realize highly relativis…
We present a new set of presupernova evolutions and explosive yields of massive stars of initial solar composition (Y=0.285, Z=0.02) in the mass range 13-35 Msun. All the models have been computed with the latest version (4.97) of the FRANEC code that now includes a nuclear network extending from neutrons to Mo98. The explosive nucleosynthesis has been computed twice: a first one with an hydro code and a second one following the simpler radiation dominated shock approximation (RDA).
We examine the characteristics of nucleosynthesis in 'hypernovae', i.e., supernovae with very large explosion energies ($ \gsim 10^{52} $ ergs). We carry out detailed nucleosynthesis calculations for these energetic explosions and compare the yields with those of ordinary core-collapse supernovae. We find that both complete and incomplete Si-burning takes place over more extended, lower density regions, so that the alpha-rich freezeout is enhanced and produces more Ti in comparison with ordinary supernova nucleosynthesis. In addition, oxygen and carbon burning takes place in more extended, low…
In this review I discuss the various gamma-ray emission lines that are expected and have been observed from radioactive explosive nucleosynthesis products. The most important gamma-ray lines result from the decay chains of Ni-56, Ni-57, and Ti-44. Ni-56 is the prime explosive nucleosynthesis product of Type Ia supernovae, but Ni-56 is also a product of core-collapse supernovae. Gamma-ray line emission from its daughter product, Co-56, has been detected from SN1987A. The early occurrence of this emission indicates that some fraction of Ni-56, which is synthesized in the innermost supernova laye…
Nuclear gamma-ray lines constitute the most genuine diagnostic tool of nuclear astrophysics, since they allow for an unambiguous identification of isotopic species. Continuous improvement in instrumentation led to the discovery of several radioactive species in the past 15 years (Al26, Co56, Co57, Ti44) in various astrophysical sites (SN1987A and SN1991T, Cas-A, the Milky Way disk). These discoveries boosted theoretical activity on the nucleosynthesis of these radioactive isotopes and on the refined modelling of the corresponding sites, improving our knowledge on stellar evolution, stellar exp…
Explosive nucleosynthesis under the axisymmetric explosion in Type II supernova has been performed by means of two dimensional hydrodynamical calculations. We have compared the results with the observations of SN 1987A. Our chief findings are as follows: (1) $^{44}Ti$ is synthesized so much as to explain the tail of the bolometric light curve of SN 1987A. We think this is because the alpha-rich freezeout takes place more actively under the axisymmetric explosion. (2) $^{57}Ni$ and $^{58}Ni$ tend to be overproduced compared with the observations. However, this tendency relies strongly on the pr…
We use the Cambridge stellar evolution code STARS to model the evolution of 5-7 solar mass zero-metallicity stars. With enhanced resolution at the hydrogen and helium burning shell in the AGB phases, we are able to model the entire thermally pulsing asymptotic giant branch (TP-AGB) phase. The helium luminosities of the thermal pulses are significantly lower than in higher metallicity stars so there is no third dredge-up. The envelope is enriched in nitrogen by hot-bottom burning of carbon that was previously mixed in during second dredge-up. There is no s-process enrichment owing to the lack o…
The most energetic part of the electromagnetic spectrum bears the purest clues to the synthesis of atomic nuclei in the universe. The decay of radioactive species, synthesized in stellar environments and ejected into the interstellar medium, gives rise to specific gamma ray lines. The observations gathered up to now show evidence for radioactivities throughout the galactic disk, in young supernova remnants (Cas A, Vela), and in nearby extragalactic supernovae (SN 1987A, SN 1991T and SN1998bu), in the form of specific gamma ray lines resulting, respectively, from the radioactive decay of 26Al, …
We carried out kinetic calculations of thermonuclear burning in the hydrogen-rich matter to simulate nucleosynthesis yields in nova outbursts. These results are used to calculate the light curves of annihilation gamma-ray line from N, O and F radioactive isotopes.
The nucleosynthesis and production of radioactive elements in SN 1987A are reviewed. Different methods for estimating the masses of 56Ni, 57Ni, and 44Ti are discussed, and we conclude that broad band photometry in combination with time-dependent models for the light curve gives the most reliable estimates.
Presupernova evolution and explosive nucleosynthesis in massive stars for main-sequence masses from 13 $M_\odot$ to 70 $M_\odot$ are calculated. We examine the dependence of the supernova yields on the stellar mass, $^{12}C(α, γ) ^{16}O}$ rate, and explosion energy. The supernova yields integrated over the initial mass function are compared with the solar abundances.
The recent detection of gamma-ray lines from radioactive Al26 and Fe60 in the Milky Way by the RHESSI satellite calls for a reassessment of the production sites of those nuclides. The observed gamma-ray line flux ratio is in agreement with calculations of nucleosynthesis in massive stars, exploding as SNII (Woosley and Weaver 1995); in the light of those results, this observation would suggest then that SNII are the major sources of Al26 in the Milky Way, since no other conceivable source produces substantial amounts of Fe60. However, more recent theoretical studies find that SNII produce much…
We investigate explosive nuclear burning in core collapse supernovae by coupling a tracer particle method to one and two-dimensional Eulerian hydrodynamic calculations. Adopting the most recent experimental and theoretical nuclear data, we compute the nucleosynthetic yields for 15 Msun stars with solar metallicity, by post-processing the temperature and density history of advected tracer particles. We compare our results to 1D calculations published in the literature.
Classical novae are fascinating stellar events, at the crossroads of astrophysics, nuclear physics and cosmochemistry. In this review, we outline the history of nova modeling with special emphasis on recent advances and perspectives in multidimensional simulations. Among the topics that are covered, we analyze the interplay between nova outbursts and the Galactic chemical abundances, the synthesis of radioactive nuclei of interest for gamma-ray astronomy, such as 7Li, 22Na or 26Al, and the recent discovery of presolar meteoritic grains, likely condensed in nova shells.
Gamma-ray line observations provide a versatile tool for studies of nucleosynthesis processes and supernova physics. In particular, the observation of radioactive species in the interstellar medium probes recent nucleosynthesis activity on various time-scales for different kinds of sources. Considerable progress in gamma-ray instrumentation during the last decades has led to the discovery of several cosmic gamma-ray lines. The best studied of these lines is today the 1.809 MeV line attributed to the decay of radioactive 26Al within the interstellar medium. In this review, recent observational …
After decades of one-dimensional nucleosynthesis calculations, the growth of computational resources has meanwhile reached a level, which for the first time allows astrophysicists to consider performing routinely realistic multidimensional nucleosynthesis calculations in explosive and, to some extent, also in non-explosive environments. In the present contribution we attempt to give a short overview of the physical and numerical problems which are encountered in these simulations. In addition, we assess the accuracy that can be currently achieved in the computation of nucleosynthetic yields, u…
We present results from the first light observations of the Cassiopeia A (Cas A) supernova remnant (SNR) by the Chandra X-ray Observatory. The X-ray spectrum varies on all spatial scales down to the instrumental limit (0.02 pc at the SNR). Based on representative spectra from four selected regions we investigate the processes of nucleosynthesis and mixing in Cas A. We make the first unequivocal identification of iron-rich ejecta produced by explosive silicon-burning in a young Galactic SNR. Elsewhere in the remnant we see silicon-rich ejecta from explosive oxygen-burning. Remarkably, our study…
We adopt up-to-date yields of 7Li, 13C, 15N from classical novae and use a well tested model for the chemical evolution of the Milky Way in order to predict the temporal evolution of these elemental species in the solar neighborhood. In spite of major uncertainties due to our lack of knowledge of metallicity effects on the final products of explosive nucleosynthesis in nova outbursts, we find a satisfactory agreement between theoretical predictions and observations for 7Li and 13C. On the contrary, 15N turns out to be overproduced by about an order of magnitude.
Proton capture by 17F plays an important role in the synthesis of nuclei in nova explosions. A revised rate for this reaction, based on a measurement of the 1H(17F,p)17F excitation function using a radioactive 17F beam at ORNL's Holifield Radioactive Ion Beam Facility, is used to calculate the nucleosynthesis in nova outbursts on the surfaces of 1.25 and 1.35 solar mass ONeMg white dwarfs and a 1.00 solar mass CO white dwarf. We find that the new 17F(p,gamma)18Ne reaction rate changes the abundances of some nuclides (e.g., 17O) synthesized in the hottest zones of an explosion on a 1.35 solar m…
The search for gamma-ray line emission from the radioactive decay of 60Fe figures among the prime scientific objectives of the INTEGRAL mission. 60Fe is believed to be primarily produced in core-collapse supernovae, although other sites, such as carbon deflagration supernovae or intermediate mass AGB stars have also been suggested. We present first results of our search for the 1173 and 1332 keV gamma-ray lines of 60Fe decay in the SPI data of the first mission year. So far we can only report upper flux limits whose levels are determined by systematic uncertainties in the treatment of the inst…
Type I X-ray bursts are violent stellar events that take place on the H/He-rich envelopes of accreting neutron stars. We have investigated the role played by uncertainties in nuclear processes on the nucleosynthesis accompanying these explosive phenomena. Two different approaches have been adopted, in the framework of post-processing calculations. In the first one, nuclear rates are varied individually within uncertainties. Ten different models, covering the characteristic parameter space for these stellar events, have been considered. The second, somewhat complementary approach involves a Mon…
Gamma-rays from radioactive 26Al (half life ~7.2 10^5 yr) provide a 'snapshot' view of ongoing nucleosynthesis in the Galaxy. The Galaxy is relatively transparent to such gamma-rays, and emission has been found concentrated along the plane of the Galaxy. This led to the conclusion1 that massive stars throughout the Galaxy dominate the production of 26Al. On the other hand, meteoritic data show locally-produced 26Al, perhaps from spallation reactions in the protosolar disk. Furthermore, prominent gamma-ray emission from the Cygnus region suggests that a substantial fraction of Galactic 26Al cou…
We investigate the effects of thermonuclear reaction rate uncertainties on nova nucleosynthesis. One-zone nucleosynthesis calculations have been performed by adopting temperature-density-time profiles of the hottest hydrogen-burning zone (i.e., the region in which most of the nucleosynthesis takes place). We obtain our profiles from 7 different, recently published, hydrodynamic nova simulations covering peak temperatures in the range from Tpeak=0.145-0.418 GK. For each of these profiles, we individually varied the rates of 175 reactions within their associated errors and analyzed the resulting…
High-resolution two-dimensional simulations were performed for the first five minutes of the evolution of a core collapse supernova explosion in a 15 solar mass blue supergiant progenitor. The computations start shortly after bounce and include neutrino-matter interactions by using a light-bulb approximation for the neutrinos, and a treatment of the nucleosynthesis due to explosive silicon and oxygen burning. We find that newly formed iron-group elements are distributed throughout the inner half of the helium core by Rayleigh-Taylor instabilities at the Ni+Si/O and C+O/He interfaces, seeded by…
One of the observational evidences in support of the "thermonuclear runaway model" for the classical nova outburst relies on the accompanying nucleosynthesis. In this paper, we stress the relevant role played by nucleosynthesis in our understanding of the nova phenomenon by constraining models through a comparison with both the atomic abundance determinations from the ejecta and the isotopic ratios measured in presolar grains of a likely nova origin. Furthermore, the endpoint of nova nucleosynthesis provides hints for the understanding of the mixing process responsible for the enhanced metalli…
Gamma-ray line observations provide a versatile tool for studies of nucleosynthesis processes and supernova physics. In particular, the observation of radioactive species in the interstellar medium probes recent nucleosynthesis activity on various time-scales for different kinds of sources. Considerable progress in gamma-ray instrumentation during the last decades has led to the discovery of several cosmic gamma-ray lines. In this review, recent observational results are presented and their astrophysical implications are discussed. Prospects of gamma-ray line astronomy will be explored in view…
Since its launch in October 2002, ESA's INTEGRAL observatory has enabled significant advances to be made in the study of Galactic nucleosynthesis. In particular, the imaging Ge spectrometer SPI combines for the first time the diagnostic powers of high resolution gamma-ray line spectroscopy and moderate spatial resolution. This review summarizes the major nucleosynthesis results obtained with INTEGRAL so far. Positron annihilation in our Galaxy is being studied in unprecented detail. SPI observations yield the first sky maps in both the 511 keV annihilation line and the positronium continuum em…
In this study we present two indicators that will reflect the difference between collapsars and normal collapse-driven supernovae. They are products of explosive nucleosynthesis and neutrino emission. In the collapsar model, it is natural to consider that the product of explosive nucleosynthesis depends on the zenith angle because the system becomes highly asymmetric in order to generate a fire ball. We also consider the detectability of the HNRs which is located nearby our Galaxy. As a result, the number of the HNRs is estimated to be 5 $\times$ ($10^2$ -- $10^{-3}$), whose chemical compositi…
In this contribution we discuss the 44Ti nucleosynthesis gamma-ray lines and their visibility with SIMBOL-X from simulations based on its expected sensitivity and spectro-imaging capabilities. The 44Ti radioactive nucleus can provide invaluable information on the details of supernova explosions. Its lifetime of about 85 yrs makes it the best indicator of the youth of these stellar explosions through its three gamma-ray lines at 67.9, 78.4 keV and 1.157 MeV. We focus on the youngest Galactic supernova remnants, namely: Cassiopeia A, for which the location and Doppler-velocity estimates of the 4…
After the recent beautiful results on gamma-ray lines obtained with CGRO, the INTEGRAL mission with the imaging-spectrometer SPI will set the next milestone, combining improved sensitivity and angular resolution with a considerable increase in spectral resolution. SPI is expected to provide significant new information on galactic nucleosynthesis processes and star formation activity, as traced by the distributions of annihilation radiation and radioactive isotopes such as 26Al and 60Fe. The unprecedented spectral resolution will allow the study of dynamic processes in stellar mass ejections an…
With the launch of ESA's INTEGRAL satellite in october 2002, a gamma-ray observatory will become available to the scientific community that combines imaging and spectroscopic capacities in the 20 keV to 10 MeV energy range. In this paper, we summarise the science prospects of the SPI spectrometer aboard INTEGRAL which provides unprecedented spectral resolution with good imaging capabilities and high sensitivity. Emphasise will be given to the key objectives of SPI which are the determination of the galactic positron origin, the study of galactic star formation and nucleosynthesis activity via …
We continue our analysis of the Galactic oxygen-rich supernova remnant (SNR) G292.0+1.8, which was observed with the {\it Chandra X-ray Observatory}. The high angular resolution {\it Chandra} data resolve metal-rich ejecta knots as well as the shocked circumstellar medium. X-ray emission from the ejecta material in G292.0+1.8 is dominated by highly ionized O, Ne and Mg. Measured abundance ratios suggest that this material was produced during the hydrostatic evolution of the massive progenitor star. In contrast to Cassiopeia A, there is little evidence for X-ray-emitting ejecta from explosive n…
