274 research outputs found
Synthetic Spectra for Type Ia Supernovae at Early Epochs
We present the current status of our construction of synthetic spectra for
type Ia supernovae. These properly take into account the effects of NLTE and an
adequate representation of line blocking and blanketing. The models are based
on a sophisticated atomic database. We show that the synthetic spectrum
reproduces the observed spectrum of 'normal' SN-Ia near maximum light from the
UV to the near-IR. However, further improvements are necessary before truly
quantitative analyses of observed SN-Ia spectra can be performed. In
particular, the inner boundary condition has to be fundamentally modified. This
is due to the dominance of electron scattering over true absorption processes
coupled with the flat density structure in these objectsComment: To appear in "Proceedings of the IAU Colloquium 192 - Supernovae (10
Years of SN1993J)", eds. J.M. Marcaide and K.W. Weile
Plasmonic gold helices for the visible range fabricated by oxygen plasma purification of electron beam induced deposits
Electron beam induced deposition (EBID) currently provides the only direct writing technique for truly three-dimensional nanostructures with geometrical features below 50 nm. Unfortunately, the depositions from metal-organic precursors suffer from a substantial carbon content. This hinders many applications, especially in plasmonics where the metallic nature of the geometric surfaces is mandatory. To overcome this problem a post-deposition treatment with oxygen plasma at room temperature was investigated for the purification of gold containing EBID structures. Upon plasma treatment, the structures experience a shrinkage in diameter of about 18 nm but entirely keep their initial shape. The proposed purification step results in a core-shell structure with the core consisting of mainly unaffected EBID material and a gold shell of about 20 nm in thickness. These purified structures are plasmonically active in the visible wavelength range as shown by dark field optical microscopy on helical nanostructures. Most notably, electromagnetic modeling of the corresponding scattering spectra verified that the thickness and quality of the resulting gold shell ensures an optical response equal to that of pure gold nanostructures
Prospect of Studying Hard X- and Gamma-Rays from Type Ia Supernovae
We perform multi-dimensional, time-dependent radiation transfer simulations
for hard X-ray and gamma-ray emissions, following radioactive decays of 56Ni
and 56Co, for two-dimensional delayed detonation models of Type Ia supernovae
(SNe Ia). The synthetic spectra and light curves are compared with the
sensitivities of current and future observatories for an exposure time of 10^6
seconds. The non-detection of the gamma-ray signal from SN 2011fe at 6.4 Mpc by
SPI on board INTEGRAL places an upper limit for the mass of 56Ni of \lesssim
1.0 Msun, independently from observations in any other wavelengths. Signals
from the newly formed radioactive species have not been convincingly measured
yet from any SN Ia, but the future X-ray and gamma-ray missions are expected to
deepen the observable horizon to provide the high energy emission data for a
significant SN Ia sample. We predict that the hard X-ray detectors on board
NuStar (launched in 2012) or ASTRO-H (scheduled for launch in 2014) will reach
to SNe Ia at \sim15 Mpc, i.e., one SN every few years. Furthermore, according
to the present results, the soft gamma-ray detector on board ASTRO-H will be
able to detect the 158 keV line emission up to \sim25 Mpc, i.e., a few SNe Ia
per year. Proposed next generation gamma-ray missions, e.g., GRIPS, could reach
to SNe Ia at \sim20 - 35 Mpc by MeV observations. Those would provide new
diagnostics and strong constraints on explosion models, detecting rather
directly the main energy source of supernova light.Comment: 14 pages, 7 figures, 1 table, accepted for publication in Ap
Optical and near-IR observations of SN 1998bw
SN 1998bw, especially after the discovery of GRB 030329/SN 2003dh, seems to
be the equivalent of the Rosetta stone for the SN/GRB connection. In this paper
I review optical and near IR observations that have been carried out for this
uncanny object, which has probably confirmed suspicions and ideas originally
formulated in the early seventies of last century.Comment: 9 pages, 7 figures. Invited review to the IAU Colloquium n. 192,
SUPERNOVAE: ten years of SN 1993J, Valencia (Spain
COMPTEL upper limits for the 56Co gamma-ray emission from SN1998bu
Supernova 1998bu in the galaxy M96 was observed by COMPTEL for a total of 88
days starting 17 days after the explosion. We searched for a signal in the 847
keV and 1238 keV lines of radioactive 56Co from this type Ia supernova. Using
several different analysis methods, we did not detect SN1998bu. Our
measurements should have been sensitive enough to detect 60Co gamma-rays as
predicted from supernova models. Our 2-sigma flux limit is 2.3 10^{-5} photons
cm^{-2} s^{-1}; this would correspond to 0.35 solar mass of ejected 56Ni, if
SN1998bu were at a distance of 11.3 Mpc and transparent to MeV gamma rays for
the period of our measurements. We discuss our measurements in the context of
common supernova models, and conclude disfavoring a supernova event with large
mixing and major parts of the freshly-generated radioactivity in outer layers.Comment: 8 pages, 6 EPS-figures, Latex2e, aa.cls needed, accepted for
publication in A&
Following multi-dimensional Type Ia supernova explosion models to homologous expansion
The last years have witnessed a rapid development of three-dimensional models
of Type Ia supernova explosions. Consequently, the next step is to evaluate
these models under variation of the initial parameters and to compare them with
observations. To calculate synthetic lightcurves and spectra from numerical
models, it is mandatory to follow the evolution up to homologous expansion. We
report on methods to achieve this in our current implementation of
multi-dimensional Type Ia supernova explosion models. The novel scheme is
thoroughly tested in two dimensions and a simple example of a three-dimensional
simulation is presented. We discuss to what degree the assumption of homologous
expansion is justified in these models.Comment: 15 pages, 16 figures, resolution of some figures reduced to meet
astro-ph file size restriction, submitted to A&
Full-star Type Ia supernova explosion models
We present full-star simulations of Type Ia supernova explosions on the basis
of the standard Chandrasekhar-mass deflagration model. Most simulations so far
considered only one spatial octant and assumed mirror symmetry to the other
octants. Two full-star models are evolved to homologous expansion and compared
with previous single-octant simulations. Therefrom we analyze the effect of
abolishing the artificial symmetry constraint on the evolution of the flame
surface. It turns out that the development of asymmetries depends on the chosen
initial flame configuration. Such asymmetries of the explosion process could
possibly contribute to the observed polarization of some Type Ia supernova
spectra.Comment: 11 pages, 10 figures, resolution of some figures reduced to meet
astro-ph file size restriction, submitted to A&
Double-detonation sub-Chandrasekhar supernovae: synthetic observables for minimum helium shell mass models
Abridged. In the double detonation scenario for Type Ia supernovae (SNe Ia) a
detonation initiates in a shell of He-rich material accreted from a companion
star by a sub-Chandrasekhar-mass White Dwarf (WD). This shell detonation drives
a shock front into the carbon-oxygen (C/O) WD that triggers a secondary
detonation in the core. The core detonation results in a complete disruption of
the WD. Earlier studies concluded that this scenario has difficulties in
accounting for the observed properties of SNe Ia since the explosion ejecta are
surrounded by the products of explosive He burning in the shell. Recently, it
was proposed that detonations might be possible for much less massive He shells
than previously assumed. Moreover, it was shown that even detonations of these
minimum He shell masses robustly trigger detonations of the C/O core. Here we
present time-dependent multi-wavelength radiative transfer calculations for
models with minimum He shell mass and derive synthetic observables for both the
optical and {\gamma}-ray spectral regions. These differ strongly from those
found in earlier simulations of sub-Chandrasekhar-mass explosions in which more
massive He shells were considered. Our models predict light curves which cover
both the range of brightnesses and the rise and decline times of observed SNe
Ia. However, their colours and spectra do not match the observations. In
particular, their B-V colours are generally too red. We show that this
discrepancy is mainly due to the composition of the burning products of the He
shell of our models which contain significant amounts of Ti and Cr. Using a toy
model, we also show that the burning products of the He shell depend crucially
on its initial composition. This leads us to conclude that good agreement
between sub-Chandrasekhar-mass explosions and observed SNe Ia may still be
feasible but further study of the shell properties is required.Comment: 17 pages, 13 figures. Accepted for publication by Ap
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