Hard X- and Gamma-Rays from Type Ia Supernovae

The gamma-ray light curves and spectra are presented for a set of theoretical Type Ia supernova models including deflagration, detonation, delayed detonation, and pulsating delayed detonations of Chandrasekhar mass white dwarfs as well as merger scenarios that may involve more than the Chandrasekhar mass and helium detonations of sub-Chandrasekhar mass white dwarfs. The results have been obtained with a Monte Carlo radiation transport scheme which takes into account all relevant gamma-transitions and interaction processes. The result is a set of accurate line profiles which are characteristic of the initial Ni-mass distribution of the supernova models. The gamma-rays probe the isotopic rather than just the elemental distribution of the radioactive elements in the ejecta. Details of the line profiles including the line width, shift with respect to the rest frame, and line ratios are discussed. With sufficient energy and temporal resolution, different model scenarios can clearly be distinguished. Observational strategies are discussed for current and immediately upcoming generations of satellites (CGRO and INTEGRAL) as well as projected future missions including concepts such as Laue telescopes. With CGRO, it is currently possible with sufficiently early observations (near optical maximum) to distinguish helium detonations from explosions of Chandrasekhar mass progenitors and of those involving mergers up to a distance of about 15 Mpc. This translates into one target of opportunity every eight years. SNe Ia up to about 10 Mpc would allow detailed CGRO studies of line ratios of Co lines.Comment: 32 pages, Tex, ApJ, in pres

Measurement of neutron capture on 48^{48}Ca at thermal and thermonuclear energies

At the Karlsruhe pulsed 3.75\,MV Van de Graaff accelerator the thermonuclear $^{48}$Ca(n,$\gamma$)$^{49}$Ca(8.72\,min) cross section was measured by the fast cyclic activation technique via the 3084.5\,keV $\gamma$-ray line of the $^{49}$Ca-decay. Samples of CaCO$_3$ enriched in $^{48}$Ca by 77.87\,\% were irradiated between two gold foils which served as capture standards. The capture cross-section was measured at the neutron energies 25, 151, 176, and 218\,keV, respectively. Additionally, the thermal capture cross-section was measured at the reactor BR1 in Mol, Belgium, via the prompt and decay $\gamma$-ray lines using the same target material. The $^{48}$Ca(n,$\gamma$)$^{49}$Ca cross-section in the thermonuclear and thermal energy range has been calculated using the direct-capture model combined with folding potentials. The potential strengths are adjusted to the scattering length and the binding energies of the final states in $^{49}$Ca. The small coherent elastic cross section of $^{48}$Ca+n is explained through the nuclear Ramsauer effect. Spectroscopic factors of $^{49}$Ca have been extracted from the thermal capture cross-section with better accuracy than from a recent (d,p) experiment. Within the uncertainties both results are in agreement. The non-resonant thermal and thermonuclear experimental data for this reaction can be reproduced using the direct-capture model. A possible interference with a resonant contribution is discussed. The neutron spectroscopic factors of $^{49}$Ca determined from shell-model calculations are compared with the values extracted from the experimental cross sections for $^{48}$Ca(d,p)$^{49}$Ca and $^{48}$Ca(n,$\gamma$)$^{49}$Ca.Comment: 15 pages (uses Revtex), 7 postscript figures (uses psfig), accepted for publication in PRC, uuencoded tex-files and postscript-files also available at ftp://is1.kph.tuwien.ac.at/pub/ohu/Ca.u

Charge-state dependence of K

Article discussing research on the charge-state dependence of K-shell x-ray production in aluminum by 2-12-MeV carbon ions