Hard X‐Rays and Gamma Rays from Type Ia Supernovae

Abstract

The γ-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 γ-transitions and interaction processes. The result is a set of accurate line profiles which are characteristic of the initial 56 Ni-mass distribution of the supernova models. The γ-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 56 Co lines. INTEGRAL will be able to perform detailed studies of the 56 Co line profiles with a range comparable to CGRO. The superior sensitivity of INTEGRAL for low energies makes detection and detailed study of the positron annhilation line and appropriate low energy 56 Ni lines possible up to about 10 -15 Mpc for all models. This capability means that this lower energy range may be the most useful for INTEGRAL detection and study of SNe Ia. Such studies will allow the determination of the precise time of the explosion. Whereas the current generation of γ-ray detectors will allow the study of supernovae which are discovered by other means, a new generation of proposed γ-ray detectors with sensitivity of about 10 −6 photons sec −1 cm −2 would generate the opportunity to discover supernovae by their γ-ray emission up to a distance of ≈ 100 Mpc. This would allow a systematic study of the variety of SNe Ia in terms of their γ-ray properties, independent of their optical properties. In addition, since γ-rays are not obscured by the host galaxy, such experiments would, for the first time, provide absolute supernova rates. Relative rates as a function of the morphology of and position in the host galaxy could be studied directly.

The Advanced Compton Telescope mission

“…ACT will measure the radioactive !-ray and positron emitters among them across the entire Milky Way, mapping our galaxy in a broad range of nuclear line emissions (Fig. E1) from radioactive decays ( 22 Na, 26 Al, 44 Ti, 60 Fe), nuclear de-excitations ( 12 C, 16 O, 56 Fe) and e + eannihilations.…”

REVEALING TYPE Ia SUPERNOVA PHYSICS WITH COSMIC RATES AND NUCLEAR GAMMA RAYS

“…The detection of gamma rays that escape the ejecta is the key to resolving the central mysteries of SNe Ia (Gehrels et al 1994;Höflich et al 1998;Boggs 2006). Since gamma rays are more penetrating and their opacities are much simpler than those for optical photons, they offer a more straightforward and direct probe of the inner mechanisms of SNe Ia Milne et al 2004;Isern et al 2008).…”

Explosive Nucleosynthesis

“…Gamma-ray spectra of SNeIa for the different models provide important signatures of the explosion mechanism, although unfortunately there isn't much observational data to compare with (see previous section). Prospects for SNeIa explosion mechanism identification with gamma-rays have been analyzed recently by Gómez-Gomar et al (1998a), with a special emphasis on detectability with the instruments that will be onboard INTEGRAL (see also Burrows and The 1990, Höflich, Khokhlov and Müller 1994, Kumagai and Nomoto 1997, Höflich, Wheeler and Khokhlov 1998.…”