15 research outputs found
A one-parameter family of interpolating kernels for Smoothed Particle Hydrodynamics studies
A set of interpolating functions of the type f(v)={(sin[v pi/2])/(v pi/2)}^n
is analyzed in the context of the smoothed-particle hydrodynamics (SPH)
technique. The behaviour of these kernels for several values of the parameter n
has been studied either analytically as well as numerically in connection with
several tests carried out in two dimensions. The main advantage of this kernel
relies in its flexibility because for n=3 it is similar to the standard widely
used cubic-spline, whereas for n>3 the interpolating function becomes more
centrally condensed, being well suited to track discontinuities such as shock
fronts and thermal waves.Comment: 36 pages, 12 figures (low-resolution), published in J.C.
Influence of geometry in the delayed detonation model of SNIa
We present several hydrodynamical simulations of thermonuclear supernovae
dealing with multiple delayed detonations. The calculations were carried out in
three dimensions, making possible to study the influence of geometry of the
flame front in two aspects. First, the evolution of its fractal dimension
during the deflagration phase has been followed until a critical value is
reached such that the deflagration may turn into a detonation. Second, as the
resulting detonation could probably be scattered through the flame, the effect
of its initial location on the detonation propagation, final energetics and
nucleosynthesis has been explored.Comment: 6 pages, 3 Figures. To appear in Proc. of the ESO/MPA/MPO Workshop:
"From Twilight to Highlight- The physics of Supernovae
Thermonuclear Supernovae: Is Deflagration Triggered by Floating Bubbles?
In recent years, it has become clear from multidimensional simulations that
the outcome of deflagrations depends strongly on the initial configuration of
the flame. We have studied under which conditions this configuration could
consist of a number of scattered, isolated, hot bubbles. Afterwards, we have
calculated the evolution of deflagrations starting from different numbers of
bubbles. We have found that starting from 30 bubbles a mild explosion is
produced M(Ni56)=0.56 solar masses, while starting from 10 bubbles the star
becomes only marginally unbound (K = 0.05 foes).Comment: 4 pages, 3 figures. To appear in Proc. of ESO/MPA/MPI Workshop: 'From
Twilight to Highliht- The physics of Supernovae
A Three-Dimensional Picture of the Delayed-Detonation Model of Type Ia Supernovae
Deflagration models poorly explain the observed diversity of SNIa. Current
multidimensional simulations of SNIa predict a significant amount of, so far
unobserved, carbon and oxygen moving at low velocities. It has been proposed
that these drawbacks can be resolved if there is a sudden jump to a detonation
(delayed detonation), but this kind of models has been explored mainly in one
dimension. Here we present new three-dimensional delayed detonation models in
which the deflagraton-to-detonation transition (DDT) takes place in conditions
like those favored by one-dimensional models. We have used a SPH code adapted
to SNIa with algorithms devised to handle subsonic as well as supersonic
combustion fronts. The starting point was a C-O white dwarf of 1.38 solar
masses. When the average density on the flame surface reached 2-3x10^7 g/cm^3 a
detonation was launched. The detonation wave processed more than 0.3 solar
masses of carbon and oxygen, emptying the central regions of the ejecta of
unburned fuel and raising its kinetic energy close to the fiducial 10^51 ergs
expected from a healthy Type Ia supernova. The final amount of 56Ni synthesized
also was in the correct range. However, the mass of carbon and oxygen ejected
is still too high. The three-dimensional delayed detonation models explored
here show an improvement over pure deflagration models, but they still fail to
coincide with basic observational constraints. However, there are many aspects
of the model that are still poorly known (geometry of flame ignition, mechanism
of DDT, properties of detonation waves traversing a mixture of fuel and ashes).
Therefore, it will be worth pursuing its exploration to see if a good SNIa
model based on the three-dimensional delayed detonation scenario can be
obtained.Comment: To appear in A&A, 12 pages, 12 figure
Beyond the bubble catastrophe of Type Ia supernovae: Pulsating Reverse Detonation models
We describe a mechanism by which a failed deflagration of a
Chandrasekhar-mass carbon-oxygen white dwarf can turn into a successful
thermonuclear supernova explosion, without invoking an ad hoc high-density
deflagration-detonation transition. Following a pulsating phase, an accretion
shock develops above a core of 1 M_sun composed of carbon and oxygen, inducing
a converging detonation. A three-dimensional simulation of the explosion
produced a kinetic energy of 1.05E51 ergs and 0.70 M_sun of 56Ni, ejecting
scarcely 0.01 M_sun of C-O moving at low velocities. The mechanism works under
quite general conditions and is flexible enough to account for the diversity of
normal Type Ia supernovae. In given conditions the detonation might not occur,
which would reflect in peculiar signatures in the gamma and UV-wavelengthsComment: Accepted for The Astrophysical Journal Letters, 12 pages, 3 figure
High temperature combustion: Approaching equilibrium using nuclear networks
A method for integrating the chemical equations associated with nuclear
combustion at high temperature is presented and extensively checked. Following
the idea of E. M\"uller, the feedback between nuclear rates and temperature was
taken into account by simultaneously computing molar fraction changes and
temperature response in the same matrix. The resulting algorithm is very stable
and efficient at calculating nuclear combustion in explosive scenarios,
especially in those situations where the reacting material manages to climb to
the nuclear statistical equilibrium regime. The numerical scheme may be useful
not only for those who carry out hydrodynamical simulations of explosive
events, but also as a tool to investigate the properties of a nuclear system
approaching equilibrium through a variety of thermodynamical trajectories.Comment: 31 pages, 11 figures, accepted for publication in the ApJ
Gravitational waves as tracers of nuclear equation of state
The signal of neutron star (NS) mergers has the imprint of the EOS of dense nuclear matter, which is still not well known. A set of gravitational waves (GW) signals have been calculated from 3D hydrodynamical simulations of NS-NS mergers using the Smoothed Particle Hydrodynamics technique (SPH) with different EOS. By analyzing the morphology and time evolution of the signal we want to be able to discriminate among the variety of proposed EOS after a successful GW detection has been done
Detailed Spectral Modeling of a 3-D Pulsating Reverse Detonation Model: Too Much Nickel
We calculate detailed NLTE synthetic spectra of a Pulsating Reverse
Detonation (PRD) model, a novel explosion mechanism for Type Ia supernovae.
While the hydro models are calculated in 3-D, the spectra use an angle averaged
hydro model and thus some of the 3-D details are lost, but the overall average
should be a good representation of the average observed spectra. We study the
model at 3 epochs: maximum light, seven days prior to maximum light, and 5 days
after maximum light. At maximum the defining Si II feature is prominent, but
there is also a prominent C II feature, not usually observed in normal SNe Ia
near maximum. We compare to the early spectrum of SN 2006D which did show a
prominent C II feature, but the fit to the observations is not compelling.
Finally we compare to the post-maximum UV+optical spectrum of SN 1992A. With
the broad spectral coverage it is clear that the iron-peak elements on the
outside of the model push too much flux to the red and thus the particular PRD
realizations studied would be intrinsically far redder than observed SNe Ia. We
briefly discuss variations that could improve future PRD models.Comment: 15 pages, 4 figures, submitted to Ap
The neutron star population in M28: a joint Chandra/GBT look at pulsar paradise
We present the results of a deep study of the neutron star (NS) population in
the globular cluster M28 (NGC 6626), using the full 330-ks 2002-2015 ACIS
dataset from the Chandra X-ray Observatory and coordinated radio observations
taken with the Green Bank Telescope (GBT) in 2015. We investigate the X-ray
luminosity (Lx), spectrum, and orbital modulation of the 7 known compact binary
millisecond pulsars (MSPs) in the cluster. We report two simultaneous
detections of the redback PSR J1824-2452I (M28I) and its X-ray counterpart. We
discover a double-peaked X-ray orbital flux modulation in M28I during its
pulsar state, centered around pulsar inferior conjunction. We analyze the
spectrum of the quiescent neutron star low-mass X-ray binary to constrain its
mass and radius. Using both hydrogen and helium NS atmosphere models, we find a
NS radius of R = 9.5-11.5 km and R = 13.5 - 16.7 km, respectively, for a
neutron star mass of 1.4 Msun. We also search for long-term variability in the
46 brightest X-ray sources and report the discovery of six new variable low
luminosity X-ray sources in M28.Comment: 26 pages, Accepted for publication in The Astrophysical Journa
Observations of SN2011fe with INTEGRAL
SN2011fe was detected by the Palomar Transient Factory on August 24th 2011 in
M101 few hours after the explosion. From the early spectra it was immediately
realized that it was a Type Ia supernova thus making this event the brightest
one discovered in the last twenty years. In this paper the observations
performed with the instruments on board of INTEGRAL (SPI, IBIS/ISGRI, JEM-X and
OMC) before and after the maximum of the optical light as well as the
interpretation in terms of the existing models of --ray emission from
such kind of supernovae are reported. All INTEGRAL high-energy have only been
able to provide upper limits to the expected emission due to the decay of
Ni. These bounds allow to reject explosions involving a massive white
dwarf in the sub--Chandrasekhar scenario. On the other hand, the optical light
curve obtained with the OMC camera suggests that the event was produced by a
delayed detonation of a CO white dwarf that produced M of
Ni. In this particular case, INTEGRAL would have only been able to
detect the early --ray emission if the supernova had occurred at a
distance of 2 -3 Mpc, although the brightest event could be visible up to
distances larger by a factor two.Comment: Proceedings of "An INTEGRAL view of the high-energy sky (the first 10
years)" the 9th INTEGRAL Workshop, October 15-19, 2012, Paris, France, in
Proceedings of Science (INTEGRAL 2012), Eds. A. Goldwurm, F. Lebrun and C.
Winkler, http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=176, id number
PoS (INTEGRAL 2012) 103 (2013