9,056 research outputs found
Insights on the physics of SNIa obtained from their gamma-ray emission
Type Ia supernovae are thought to be the outcome of the thermonuclear
explosion of a carbon/oxygen white dwarf in a close binary system. Their
optical light curve is powered by thermalized gamma-rays produced by the
radioactive decay of Ni, the most abundant isotope present in the
debris. Gamma-rays escaping the ejecta can be used as a diagnostic tool for
studying the structure of the exploding star and the characteristics of the
explosion. The fluxes of the Ni lines and the continuum obtained by
INTEGRAL from SN2014J in M82, the first ever gamma-detected SNIa, around the
time of the maximum of the optical light curve strongly suggest the presence of
a plume of Ni in the outermost layers moving at high velocities. If this
interpretation was correct, it could have important consequences on our current
understanding of the physics of the explosion and on the nature of the systems
that explode.Comment: Proceedings of the 11th INTEGRAL Conference Gamma-Ray AStrophysics in
Multi-Wavelength Perspectiv
Exploring the Physics of Type Ia Supernovae Through the X-ray Spectra of their Remnants
We present the results of an ongoing project to use the X-ray observations of
Type Ia Supernova Remnants to constrain the physical processes involved in Type
Ia Supernova explosions. We use the Tycho Supernova Remnant (SN 1572) as a
benchmark case, comparing its observed spectrum with models for the X-ray
emission from the shocked ejecta generated from different kinds of Type Ia
explosions. Both the integrated spectrum of Tycho and the spatial distribution
of the Fe and Si emission in the remnant are well reproduced by delayed
detonation models with stratified ejecta. All the other Type Ia explosion
models fail, including well-mixed deflagrations calculated in three dimensions.Comment: 5 pages, 3 figures, to appear in the proceedings of the "Stellar end
products" workshop, 13-15 April 2005, Granada, Spain, ed. M.A. Perez-Torres,
Vol. 77 (Jan 2006) of MmSA
Explosion of white dwarfs harboring hybrid CONe cores
Recently, it has been found that off-centre carbon burning in a subset of
intermediate-mass stars does not propagate all the way to the center, resulting
in a class of hybrid CONe cores. Here, we consider the possibility that stars
hosting these hybrid CONe cores might belong to a close binary system and,
eventually, become white dwarfs accreting from a non-degenerate companion at
rates leading to a supernova explosion. We have computed the hydrodynamical
phase of the explosion of Chandrasekhar-mass white dwarfs harboring hybrid
cores, assuming that the explosion starts at the center, either as a detonation
(as may be expected in some degenerate merging scenarios) or as a deflagration
(that afterwards transitions into a delayed detonation). We assume these hybrid
cores are made of a central CO volume, of mass M(CO), surrounded by an ONe
shell. We show that, in case of a pure detonation, a medium-sized CO-rich
region, M(CO)<0.4 Msun, results in the ejection of a small fraction of the
mantle while leaving a massive bound remnant. Part of this remnant is made of
the products of the detonation, Fe-group nuclei, but they are buried in its
inner regions, unless convection is activated during the ensuing cooling and
shrinking phase of the remnant. In contrast, and somehow paradoxically, delayed
detonations do not leave remnants but for the minimum M(CO) we have explored,
M(CO)=0.2 Msun, and even in this case the remnant is as small as 0.13 Msun. The
ejecta produced by these delayed detonations are characterized by slightly
smaller masses of 56Ni and substantially smaller kinetic energies than obtained
for a delayed detonation of a 'normal' CO white dwarf. The optical emission
expected from these explosions would hardly match the observational properties
of typical Type Ia supernovae, although they make interesting candidates for
the subluminous class of SN2002cx-like or SNIax.Comment: Accepted for Astronomy and Astrophysics, 11 pages, 4 figure
Wavelets: a powerful tool for studying rotation, activity, and pulsation in Kepler and CoRoT stellar light curves
Aims. The wavelet transform has been used as a powerful tool for treating
several problems in astrophysics. In this work, we show that the time-frequency
analysis of stellar light curves using the wavelet transform is a practical
tool for identifying rotation, magnetic activity, and pulsation signatures. We
present the wavelet spectral composition and multiscale variations of the time
series for four classes of stars: targets dominated by magnetic activity, stars
with transiting planets, those with binary transits, and pulsating stars.
Methods. We applied the Morlet wavelet (6th order), which offers high time and
frequency resolution. By applying the wavelet transform to the signal, we
obtain the wavelet local and global power spectra. The first is interpreted as
energy distribution of the signal in time-frequency space, and the second is
obtained by time integration of the local map. Results. Since the wavelet
transform is a useful mathematical tool for nonstationary signals, this
technique applied to Kepler and CoRoT light curves allows us to clearly
identify particular signatures for different phenomena. In particular, patterns
were identified for the temporal evolution of the rotation period and other
periodicity due to active regions affecting these light curves. In addition, a
beat-pattern signature in the local wavelet map of pulsating stars over the
entire time span was also detected.Comment: Accepted for publication on A&
Properties of Deflagration Fronts and Models for Type Ia Supernovae
Detailed models of the explosion of a white dwarf, which include
self-consistent calculations of the light curve and spectra, provide a link
between observational quantities and the underlying explosion.These
calculations assume spherical geometry and are based on parameterized
descriptions of the burning front during the deflagration phase. Recently,
first multi-dimensional calculations for nuclear burning fronts have been
performed. Although a fully consistent treatment of the burning fronts is
beyond the current state of the art, these calculations provided a new and
better understanding of the physics, and new descriptions for the flame
propagation have been proposed. Here, we have studied the influence on the
results of previous analyses of Type Ia Supernovae, namely, the nucleosynthesis
and structure of the expanding envelope. Our calculations are based on a set of
delayed detonation models with parameters that give a good account of the
optical and infrared light curves, and of the spectral evolution. In this
scenario, the burning front propagates first in a deflagration mode and,
subsequently, turns into a detonation. The explosions and light curves are
calculated using a one-dimensional Lagrangian radiation-hydro code, including a
detailed nuclear network.Comment: 9 pages, 4 figures, macros 'crckapb.sty'. The Astrophysical Journal
(accepted
Resonant transmission of light through finite chains of subwavelength holes
In this paper we show that the extraordinary optical transmission phenomenon
found before in 2D hole arrays is already present in a linear chain of
subwavelength holes, which can be considered as the basic geometrical unit
showing this property. In order to study this problem we have developed a new
theoretical framework, able to analyze the optical properties of finite
collections of subwavelength apertures and/or dimples (of any shape and placed
in arbitrary positions) drilled in a metallic film.Comment: Accepted for publication in Phys. Rev. Let
Gamma-rays from Type Ia supernova SN2014J
The whole set of INTEGRAL observations of type Ia supernova SN2014J, covering
the period 19-162 days after the explosion has being analyzed. For spectral
fitting the data are split into "early" and "late" periods covering days 19-35
and 50-162, respectively, optimized for Ni and Co lines. As
expected for the early period much of the gamma-ray signal is confined to
energies below 200 keV, while for the late period it is most strong above
400 keV. In particular, in the late period Co lines at 847 and 1248 keV
are detected at 4.7 and 4.3 respectively. The lightcurves in several
representative energy bands are calculated for the entire period. The resulting
spectra and lightcurves are compared with a subset of models. We confirm our
previous finding that the gamma-ray data are broadly consistent with the
expectations for canonical 1D models, such as delayed detonation or
deflagration models for a near-Chandrasekhar mass WD. Late optical spectra (day
136 after the explosion) show rather symmetric Co and Fe lines profiles,
suggesting that unless the viewing angle is special, the distribution of
radioactive elements is symmetric in the ejecta.Comment: 21 pages, 16 figures, accepted by Ap
Type Ia Supernova Scenarios and the Hubble Sequence
The dependence of the Type Ia supernova (SN Ia) rate on galaxy type is
examined for three currently proposed scenarios: merging of a
Chandrasekhar--mass CO white dwarf (WD) with a CO WD companion, explosion of a
sub--Chandrasekhar mass CO WD induced by accretion of material from a He star
companion, and explosion of a sub--Chandrasekhar CO WD in a symbiotic system.
The variation of the SNe Ia rate and explosion characteristics with time is
derived, and its correlation with parent population age and galaxy redshift is
discussed. Among current scenarios, CO + He star systems should be absent from
E galaxies. Explosion of CO WDs in symbiotic systems could account for the SNe
Ia rate in these galaxies. The same might be true for the CO + CO WD scenario,
depending on the value of the common envelope parameter. A testable prediction
of the sub--Chandrasekhar WD model is that the average brightness and kinetic
energy of the SN Ia events should increase with redshift for a given Hubble
type. Also for this scenario, going along the Hubble sequence from E to Sc
galaxies SNe Ia events should be brighter on average and should show larger
mean velocities of the ejecta. The observational correlations strongly suggest
that the characteristics of the SNe Ia explosion are linked to parent
population age. The scenario in which WDs with masses below the Chandrasekhar
mass explode appears the most promising one to explain the observed variation
of the SN Ia rate with galaxy type together with the luminosity--expansion
velocity trend.Comment: 16 pages uuencoded compressed Postscript, 2 figures included. ApJ
Letters, in pres
Efficient low-power terahertz generation via on-chip triply-resonant nonlinear frequency mixing
Achieving efficient terahertz (THz) generation using compact turn-key sources
operating at room temperature and modest power levels represents one of the
critical challeges that must be overcome to realize truly practical
applications based on THz. Up to now, the most efficient approaches to THz
generation at room temperature -- relying mainly on optical rectification
schemes -- require intricate phase-matching set-ups and powerful lasers. Here
we show how the unique light-confining properties of triply-resonant photonic
resonators can be tailored to enable dramatic enhancements of the conversion
efficiency of THz generation via nonlinear frequency down-conversion processes.
We predict that this approach can be used to reduce up to three orders of
magnitude the pump powers required to reach quantum-limited conversion
efficiency of THz generation in nonlinear optical material systems.
Furthermore, we propose a realistic design readily accesible experimentally,
both for fabrication and demonstration of optimal THz conversion efficiency at
sub-W power levels
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