33 research outputs found
Expectations for the Hard X-ray Continuum and Gamma-ray Line Fluxes from the Type Ia supernova SN 2014J in M82
The hard X-ray continuum and gamma-ray lines from a Type Ia supernova
dominate its integrated photon emissions and can provide unique diagnostics of
the mass of the ejecta, the Ni yield and spatial distribution, its
kinetic energy and expansion speed, and the mechanism of explosion. Such
signatures and their time behavior "X-ray" the bulk debris field in direct
fashion, and do not depend upon the oftimes problematic and elaborate UV,
optical, and near-infrared spectroscopy and radiative transfer that have
informed the study of these events for decades. However, to date no hard
photons have ever been detected from a Type Ia supernova in explosion. With the
advent of the supernova SN 2014J in M82, at a distance of 3.5 Mpc, this
situation may soon change. Both NuSTAR and INTEGRAL have the potential to
detect SN 2014J, and, if spectra and light curves can be measured, would
usefully constrain the various explosion models published during the last
thirty years. In support of these observational campaigns, we provide
predictions for the hard X-ray continuum and gamma-line emissions for fifteen
Type Ia explosion models gleaned from the literature. The model set, containing
as it does deflagration, delayed detonation, merger detonation, pulsational
delayed detonation, and sub-Chandrasekhar helium detonation models,
collectively spans a wide range of properties and, hence, signatures. We
provide a brief discussion of various diagnostics (with examples), but
importantly make the spectral and line results available electronically to aid
in the interpretation of the anticipated data.Comment: Accepted to the Astrophysical Journal (March 31, 2014), with one
additional figure and further discussion of techniqu
The Cosmic Gamma-Ray Background from Type Ia Supernovae
We present an improved calculation of the cumulative gamma-ray spectrum of Type Ia supernovae during the history of the universe. We follow Clayton & Ward (1975) in using a few Friedmann models and two simple histories of the average galaxian nucleosynthesis rate, but we improve their calculation by modeling the gamma-ray scattering in detailed numerical models of SN Ia\u27s. The results confirm that near 1 MeV the SN Ia background may dominate, and that it is potentially observable, with high scientific importance. A very accurate measurement of the cosmic background spectrum between 0.1 and 1.0 MeV may reveal the turn-on time and the evolution of the rate of Type Ia supernova nucleosynthesis in the universe
Energy Deposition and K-Shell Ionization of Supernovae
We present explicit evaluation of K-shell ionization caused by photoelectric absorption, by Compton scattering, and by electron collisions in supernovae envelopes. Each process derives from the radioactivity that dominates the bolometric luminosity of the model supernovae. We include the ionization by bremsstrahlung. We find that electron-collision ionization with decelerating Compton electrons is the dominant process of K-shell ionization for light elements (lighter than Si) whereas photoelectric K-shell absorption of Comptonized gammas is the dominant process of K-shell ionization for heavy elements (like Fe). The relative importance of the ionization processes also depends upon composition and upon time, as well as upon supernova type. For Type Ia all four ionization sources are of importance. We present fitting formulas for the deposition of radioactive power in each class of models studied. The energy deposition of all mechanisms decreases with time, including the rate of K-shell ionizations of all elements throughout the supernovae model evaluated herein. We compare the relative contributions to the energy deposition and confirm with greater numerical detail results already established
Gamma-Ray Constraints on the Galactic Supernova Rate
Monte Carlo simulations of the expected gamma-ray signatures of galactic supernovae of all types are performed in order to estimate the significance of the lack of a gamma-ray signal due to supernovae occurring during the last millenium. Using recent estimates of nuclear yields, we determine galactic supernova rates consistent with the historic supernova record and the gamma-ray limits. Another objective of these calculations of galactic supernova histories is their application to surveys of diffuse galactic gamma-ray line emission
The origin of the cosmic gamma-ray background in the MeV range
There has been much debate about the origin of the diffuse --ray
background in the MeV range. At lower energies, AGNs and Seyfert galaxies can
explain the background, but not above 0.3 MeV. Beyond 10 MeV
blazars appear to account for the flux observed. That leaves an unexplained gap
for which different candidates have been proposed, including annihilations of
WIMPS. One candidate are Type Ia supernovae (SNe Ia). Early studies concluded
that they were able to account for the --ray background in the gap,
while later work attributed a significantly lower contribution to them.
All those estimates were based on SN Ia explosion models which did not
reflect the full 3D hydrodynamics of SNe Ia explosions. In addition, new
measurements obtained since 2010 have provided new, direct estimates of high-z
SNe Ia rates beyond 2. We take into account these new advances to see
the predicted contribution to the gamma--ray background.
We use here a wide variety of explosion models and a plethora of new
measurements of SNe Ia rates. SNe Ia still fall short of the observed
background. Only for a fit, which would imply 150\% systematic error in
detecting SNe Ia events, do the theoretical predictions approach the observed
fluxes. This fit is, however, at odds at the highest redshifts with recent SN
Ia rates estimates. Other astrophysical sources such as FSRQs do match the
observed flux levels in the MeV regime, while SNe Ia make up to 30--50\% of the
observed flux.Comment: 40 pages, 13 Figures, accepted to be published in Ap
s-Process Nucleosynthesis in Advanced Burning Phases of Massive Stars
We present a detailed study of s-process nucleosynthesis in massive stars of
solar-like initial composition and masses 15, 20,25, and 30 Msun. We update our
previous results of s-process nucleosynthesis during the core He-burning of
these stars and then focus on an analysis of the s-process under the physical
conditions encountered during the shell-carbon burning. We show that the recent
compilation of the Ne22(alpha,n)Mg25 rate leads to a remarkable reduction of
the efficiency of the s-process during core He-burning. In particular, this
rate leads to the lowest overproduction factor of Kr80 found to date during
core He-burning in massive stars. The s-process yields resulting from shell
carbon burning turn out to be very sensitive to the structural evolution of the
carbon shell. This structure is influenced by the mass fraction of C12 attained
at the end of core helium burning, which in turn is mainly determined by the
C12(alpha,gamma)O16 reaction. The still present uncertainty in the rate for
this reaction implies that the s-process in massive stars is also subject to
this uncertainty. We identify some isotopes like Zn70 and Rb87 as the
signatures of the s-process during shell carbon burning in massive stars. In
determining the relative contribution of our s-only stellar yields to the solar
abundances, we find it is important to take into account the neutron exposure
of shell carbon burning. When we analyze our yields with a Salpeter Initial
Mass Function, we find that massive stars contribute at least 40% to s-only
nuclei with mass A 90, massive stars
contribute on average ~7%, except for Gd152, Os187, and Hg198 which are ~14%,
\~13%, and ~11%, respectively.Comment: 52 pages, 16 figures, accepted for publication in Ap
The Co-57 Abundance in SN 1987A
Astrophysical implications of the detection by OSSE of Co-57 gamma radiation from SN 1987A are discussed. By burying the alpha-rich-freezeout portion at deeper gamma depths than in published models, it is shown that it remains barely possible that the bolometric luminosity during days 1200-1800 could derive from Co-57 power without requiring 57/56 production ratios greater than twice solar. Alternative mechanisms which may contribute to the bolometric power at late times are proposed
The 57Co Abundance in SN 1987A
We discuss several astrophysical consequences of the detection by OSSE (Kurfess et al. 1992) of 57Co gamma radiation from supernova 1987A. Models with low photoelectric absorption cannot account for both OSSE data and the bolometric luminosity. By burying the alpha-rich-freezeout portion at deeper gamma depths than in published models, we show that it remains barely possible that the bolometric luminosity during days 1200-1800 could derive from 57Co power without requiring 57/56 production ratios greater than twice solar. We illustrate this by slowing the expansion within the inner four solar masses of ejecta in model 10HMM