1,094 research outputs found
A reddening-free method to estimate the Ni mass of Type Ia supernovae
The increase in the number of Type Ia supernovae (SNe\,Ia) has demonstrated
that the population shows larger diversity than has been assumed in the past.
The reasons (e.g. parent population, explosion mechanism) for this diversity
remain largely unknown. We have investigated a sample of SNe\,Ia near-infrared
light curves and have correlated the phase of the second maximum with the
bolometric peak luminosity. The peak bolometric luminosity is related to the
time of the second maximum (relative to the {\it B} light curve maximum) as
follows : .
Ni masses can be derived from the peak luminosity based on Arnett's
rule, which states that the luminosity at maximum is equal to instantaneous
energy generated by the nickel decay. We check this assumption against recent
radiative-transfer calculations of Chandrasekhar-mass delayed detonation models
and find this assumption is valid to within 10\% in recent radiative-transfer
calculations of Chandrasekhar-mass delayed detonation models.
The vs. relation is applied to a sample of 40 additional
SNe\,Ia with significant reddening ( 0.1 mag) and a reddening-free
bolometric luminosity function of SNe~Ia is established. The method is tested
with the Ni mass measurement from the direct observation of
rays in the heavily absorbed SN 2014J and found to be fully
consistent.
Super-Chandrasekhar-mass explosions, in particular SN\,2007if, do not follow
the relations between peak luminosity and second IR maximum. This may point to
an additional energy source contributing at maximum light.
The luminosity function of SNe\,Ia is constructed and is shown to be
asymmetric with a tail of low-luminosity objects and a rather sharp
high-luminosity cutoff, although it might be influenced by selection effects.Comment: 9 pages, 3 figures, Accepted to A&
3D simulations of Rayleigh-Taylor mixing in core-collapse SNe with CASTRO
We present multidimensional simulations of the post-explosion hydrodynamics
in three different 15 solar mass supernova models with zero, 10^{-4} solar
metallicity, and solar metallicities. We follow the growth of the
Rayleigh-Taylor instability that mixes together the stellar layers in the wake
of the explosion. Models are initialized with spherically symmetric explosions
and perturbations are seeded by the grid. Calculations are performed in
two-dimensional axisymmetric and three-dimensional Cartesian coordinates using
the new Eulerian hydrodynamics code, CASTRO. We find as in previous work, that
Rayleigh-Taylor perturbations initially grow faster in 3D than in 2D. As the
Rayleigh-Taylor fingers interact with one another, mixing proceeds to a greater
degree in 3D than in 2D, reducing the local Atwood number and slowing the
growth rate of the instability in 3D relative to 2D. By the time mixing has
stopped, the width of the mixed region is similar in 2D and 3D simulations
provided the Rayleigh-Taylor fingers show significant interaction. Our results
imply that 2D simulations of light curves and nucleosynthesis in supernovae
(SNe) that die as red giants may capture the features of an initially
spherically symmetric explosion in far less computational time than required by
a full 3D simulation. However, capturing large departures from spherical
symmetry requires a significantly perturbed explosion. Large scale asymmetries
cannot develop through an inverse cascade of merging Rayleigh-Taylor
structures; they must arise from asymmetries in the initial explosion.Comment: 12 pages, 5 figures, ApJ accepte
2D and 3D Core-Collapse Supernovae Simulation Results Obtained with the CHIMERA Code
Much progress in realistic modeling of core-collapse supernovae has occurred
recently through the availability of multi-teraflop machines and the increasing
sophistication of supernova codes. These improvements are enabling simulations
with enough realism that the explosion mechanism, long a mystery, may soon be
delineated. We briefly describe the CHIMERA code, a supernova code we have
developed to simulate core-collapse supernovae in 1, 2, and 3 spatial
dimensions. We then describe the results of an ongoing suite of 2D simulations
initiated from a 12, 15, 20, and 25 solar mass progenitor. These have all
exhibited explosions and are currently in the expanding phase with the shock at
between 5,000 and 20,000 km. We also briefly describe an ongoing simulation in
3 spatial dimensions initiated from the 15 solar mass progenitor.Comment: 5 pages, 3 figure
Ascertaining the Core Collapse Supernova Mechanism: An Emerging Picture?
Here we present the results from two sets of simulations, in two and three
spatial dimensions. In two dimensions, the simulations include multifrequency
flux-limited diffusion neutrino transport in the "ray-by-ray-plus"
approximation, two-dimensional self gravity in the Newtonian limit, and nuclear
burning through a 14-isotope alpha network. The three-dimensional simulations
are model simulations constructed to reflect the post stellar core bounce
conditions during neutrino shock reheating at the onset of explosion. They are
hydrodynamics-only models that focus on critical aspects of the shock stability
and dynamics and their impact on the supernova mechanism and explosion. In two
dimensions, we obtain explosions (although in one case weak) for two
progenitors (11 and 15 Solar mass models). Moreover, in both cases the
explosion is initiated when the inner edge of the oxygen layer accretes through
the shock. Thus, the shock is not revived while in the iron core, as previously
discussed in the literature. The three-dimensional studies of the development
of the stationary accretion shock instability (SASI) demonstrate the
fundamentally new dynamics allowed when simulations are performed in three
spatial dimensions. The predominant l=1 SASI mode gives way to a stable m=1
mode, which in turn has significant ramifications for the distribution of
angular momentum in the region between the shock and proto-neutron star and,
ultimately, for the spin of the remnant neutron star. Moreover, the
three-dimensional simulations make clear, given the increased number of degrees
of freedom, that two-dimensional models are severely limited by artificially
imposed symmetries.Comment: 9 pages, 3 figure
Supernova cosmology: legacy and future
The discovery of dark energy by the first generation of high-redshift
supernova surveys has generated enormous interest beyond cosmology and has
dramatic implications for fundamental physics. Distance measurements using
supernova explosions are the most direct probes of the expansion history of the
Universe, making them extremely useful tools to study the cosmic fabric and the
properties of gravity at the largest scales. The past decade has seen the
confirmation of the original results. Type Ia supernovae are among the leading
techniques to obtain high-precision measurements of the dark energy equation of
state parameter, and in the near future, its time dependence. The success of
these efforts depends on our ability to understand a large number of effects,
mostly of astrophysical nature, influencing the observed flux at Earth. The
frontier now lies in understanding if the observed phenomenon is due to vacuum
energy, albeit its unnatural density, or some exotic new physics. Future
surveys will address the systematic effects with improved calibration
procedures and provide thousands of supernovae for detailed studies.Comment: Invited review, Annual Review of Nuclear and Particle Science
(submitted version
On the Interpretation of Supernova Light Echo Profiles and Spectra
The light echo systems of historical supernovae in the Milky Way and local
group galaxies provide an unprecedented opportunity to reveal the effects of
asymmetry on observables, particularly optical spectra. Scattering dust at
different locations on the light echo ellipsoid witnesses the supernova from
different perspectives and the light consequently scattered towards Earth
preserves the shape of line profile variations introduced by asymmetries in the
supernova photosphere. However, the interpretation of supernova light echo
spectra to date has not involved a detailed consideration of the effects of
outburst duration and geometrical scattering modifications due to finite
scattering dust filament dimension, inclination, and image point-spread
function and spectrograph slit width. In this paper, we explore the
implications of these factors and present a framework for future resolved
supernova light echo spectra interpretation, and test it against Cas A and SN
1987A light echo spectra. We conclude that the full modeling of the dimensions
and orientation of the scattering dust using the observed light echoes at two
or more epochs is critical for the correct interpretation of light echo
spectra. Indeed, without doing so one might falsely conclude that differences
exist when none are actually present.Comment: 18 pages, 22 figures, accepted for publication in Ap
PHotometry Assisted Spectral Extraction (PHASE) and identification of SNLS supernovae
Aim: We present new extraction and identification techniques for supernova
(SN) spectra developed within the Supernova Legacy Survey (SNLS) collaboration.
Method: The new spectral extraction method takes full advantage of
photometric information from the Canada-France-Hawai telescope (CFHT) discovery
and reference images by tracing the exact position of the supernova and the
host signals on the spectrogram. When present, the host spatial profile is
measured on deep multi-band reference images and is used to model the host
contribution to the full (supernova + host) signal. The supernova is modelled
as a Gaussian function of width equal to the seeing. A chi-square minimisation
provides the flux of each component in each pixel of the 2D spectrogram. For a
host-supernova separation greater than <~ 1 pixel, the two components are
recovered separately and we do not use a spectral template in contrast to more
standard analyses. This new procedure permits a clean extraction of the
supernova separately from the host in about 70% of the 3rd year ESO/VLT spectra
of the SNLS. A new supernova identification method is also proposed. It uses
the SALT2 spectrophotometric template to combine the photometric and spectral
data. A galaxy template is allowed for spectra for which a separate extraction
of the supernova and the host was not possible.
Result: These new techniques have been tested against more standard
extraction and identification procedures. They permit a secure type and
redshift determination in about 80% of cases. The present paper illustrates
their performances on a few sample spectra.Comment: 27 pages, 18 Figures, 1 Table. Accepted for publication in A&
Spectroscopy of High-Redshift Supernovae from the ESSENCE Project: The First Four Years
We present the results of spectroscopic observations from the ESSENCE
high-redshift supernova (SN) survey during its first four years of operation.
This sample includes spectra of all SNe Ia whose light curves were presented by
Miknaitis et al. (2007) and used in the cosmological analyses of Davis et al.
(2007) and Wood-Vasey et al. (2007). The sample represents 273 hours of
spectroscopic observations with 6.5 - 10-m-class telescopes of objects detected
and selected for spectroscopy by the ESSENCE team. We present 174 spectra of
156 objects. Combining this sample with that of Matheson et al. (2005), we have
a total sample of 329 spectra of 274 objects. From this, we are able to
spectroscopically classify 118 Type Ia SNe. As the survey has matured, the
efficiency of classifying SNe Ia has remained constant while we have observed
both higher-redshift SNe Ia and SNe Ia farther from maximum brightness.
Examining the subsample of SNe Ia with host-galaxy redshifts shows that
redshifts derived from only the SN Ia spectra are consistent with redshifts
found from host-galaxy spectra. Moreover, the phases derived from only the SN
Ia spectra are consistent with those derived from light-curve fits. By
comparing our spectra to local templates, we find that the rate of objects
similar to the overluminous SN 1991T and the underluminous SN 1991bg in our
sample are consistent with that of the local sample. We do note, however, that
we detect no object spectroscopically or photometrically similar to SN 1991bg.
Although systematic effects could reduce the high-redshift rate we expect based
on the low-redshift surveys, it is possible that SN 1991bg-like SNe Ia are less
prevalent at high redshift.Comment: 21 pages, 17 figures, accepted to A
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