443 research outputs found
Oxygen emission in remnants of thermonuclear supernovae as a probe for their progenitor system
Recent progress in numerical simulations of thermonuclear supernova
explosions brings up a unique opportunity in studying the progenitors of Type
Ia supernovae. Coupling state-of-the-art explosion models with detailed
hydrodynamical simulations of the supernova remnant evolution and the most
up-to-date atomic data for X-ray emission calculations makes it possible to
create realistic synthetic X-ray spectra for the supernova remnant phase.
Comparing such spectra with high quality observations of supernova remnants
could allow to constrain the explosion mechanism and the progenitor of the
supernova. The present study focuses in particular on the oxygen emission line
properties in young supernova remnants, since different explosion scenarios
predict a different amount and distribution of this element. Analysis of the
soft X-ray spectra from supernova remnants in the Large Magellanic Cloud and
confrontation with remnant models for different explosion scenarios suggests
that SNR 0509-67.5 could originate from a delayed detonation explosion and SNR
0519-69.0 from an oxygen-rich merger.Comment: 8 pages, 4 figures, MNRAS accepte
Deflagrations in hybrid CONe white dwarfs: a route to explain the faint Type Iax supernova 2008ha
Stellar evolution models predict the existence of hybrid white dwarfs (WDs)
with a carbon-oxygen core surrounded by an oxygen-neon mantle. Being born with
masses ~1.1 Msun, hybrid WDs in a binary system may easily approach the
Chandrasekhar mass (MCh) by accretion and give rise to a thermonuclear
explosion. Here, we investigate an off-centre deflagration in a near-MCh hybrid
WD under the assumption that nuclear burning only occurs in carbon-rich
material. Performing hydrodynamics simulations of the explosion and detailed
nucleosynthesis post-processing calculations, we find that only 0.014 Msun of
material is ejected while the remainder of the mass stays bound. The ejecta
consist predominantly of iron-group elements, O, C, Si and S. We also calculate
synthetic observables for our model and find reasonable agreement with the
faint Type Iax SN 2008ha. This shows for the first time that deflagrations in
near-MCh WDs can in principle explain the observed diversity of Type Iax
supernovae. Leaving behind a near-MCh bound remnant opens the possibility for
recurrent explosions or a subsequent accretion-induced collapse in faint Type
Iax SNe, if further accretion episodes occur. From binary population synthesis
calculations, we find the rate of hybrid WDs approaching MCh to be on the order
of 1 percent of the Galactic SN Ia rate.Comment: 9 pages, 7 figures, 2 tables, accepted for publication in MNRA
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
The peculiar Type Ia supernova iPTF14atg: Chandrasekhar-mass explosion or violent merger?
iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN
2002es, is the first SN Ia for which a strong UV flash was observed in the
early-time light curves. This has been interpreted as evidence for a
single-degenerate (SD) progenitor system where such a signal is expected from
interactions between the SN ejecta and the non-degenerate companion star. Here,
we compare synthetic observables of multi-dimensional state-of-the-art
explosion models for different progenitor scenarios to the light curves and
spectra of iPTF14atg. From our models, we have difficulties explaining the
spectral evolution of iPTF14atg within the SD progenitor channel. In contrast,
we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and
0.76 solar masses, respectively, provides an excellent match to the spectral
evolution of iPTF14atg from 10d before to several weeks after maximum light.
Our merger model does not naturally explain the initial UV flash of iPTF14atg.
We discuss several possibilities like interactions of the SN ejecta with the
circum-stellar medium and surface radioactivity from a He ignited merger that
may be able to account for the early UV emission in violent merger models.Comment: 12 pages, 7 figures, accepted for publication in MNRA
Gamma-ray diagnostics of Type Ia supernovae: Predictions of observables from three-dimensional modeling
Besides the fact that the gamma-ray emission due to radioactive decays is
responsible for powering the light curves of Type Ia supernovae (SNe Ia), gamma
rays themselves are of particular interest as a diagnostic tool because they
provide a direct way to obtain deeper insights into the nucleosynthesis and the
kinematics of these explosion events. Focusing on two of the most broadly
discussed SN Ia progenitor scenarios - a delayed detonation in a
Chandrasekhar-mass white dwarf (WD) and a violent merger of two WDs - we use
three-dimensional explosion models and perform radiative transfer simulations
to obtain synthetic gamma-ray spectra. Both chosen models produce the same mass
of 56Ni and have similar optical properties that are in reasonable agreement
with the recently observed supernova SN 2011fe. In contrast to the optical
regime, the gamma-ray emission of our two chosen models proves to be rather
different. The almost direct connection of the emission of gamma rays to
fundamental physical processes occuring in SNe Ia permits additional
constraints concerning several explosion model properties that are not easily
accessible within other wavelength ranges. Proposed future MeV missions such as
GRIPS will resolve all spectral details only for nearby SNe Ia, but hardness
ratio and light curve measurements still allow for a distinction of the two
different models at 10 and 16 Mpc for an exposure time of 10^6 s, respectively.
The possibility to detect the strongest line features up to the Virgo distance
will offer the opportunity to build up a first sample of SN Ia detections in
the gamma-ray energy range and underlines the importance of future space
observatories for MeV gamma rays.Comment: 10 pages, 8 figures, accepted for publication by A&
Thermonuclear explosions of rapidly differentially rotating white dwarfs: Candidates for superluminous Type Ia supernovae?
The observed sub-class of "superluminous" Type Ia supernovae lacks a
convincing theoretical explanation. If the emission of such objects were
powered exclusively by radioactive decay of 56Ni formed in the explosion, a
progenitor mass close to or even above the Chandrasekhar limit for a
non-rotating white dwarf star would be required. Masses significantly exceeding
this limit can be supported by differential rotation. We, therefore, explore
explosions and predict observables for various scenarios resulting from
differentially rotating carbon-oxygen white dwarfs close to their respective
limit of stability. Specifically, we have investigated a prompt detonation
model, detonations following an initial deflagration phase ("delayed
detonation" models), and a pure deflagration model. In postprocessing steps, we
performed nucleosynthesis and three-dimensional radiative transfer
calculations, that allow us, for the first time, to consistently derive
synthetic observables from our models. We find that all explosion scenarios
involving detonations produce very bright events. The observables predicted for
them, however, are inconsistent with any known subclass of Type Ia supernovae.
Pure deflagrations resemble 2002cx-like supernovae and may contribute to this
class. We discuss implications of our findings for the explosion mechanism and
for the existence of differentially rotating white dwarfs as supernova
progenitors.Comment: 12 pages, 9 figures, 2 tables, accepted for publication in A&A. Model
data are available from the Heidelberg Supernova Model Archive (HESMA) at
https://hesma.h-its.org
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
Sub-luminous type Ia supernovae from the mergers of equal-mass white dwarfs with M~0.9 M_sun
Type Ia supernovae (SNe Ia) are thought to result from thermonuclear
explosions of carbon-oxygen white dwarf stars. Existing models generally
explain the observed properties, with the exception of the sub-luminous
1991-bg-like supernovae. It has long been suspected that the merger of two
white dwarfs could give rise to a type Ia event, but hitherto simulations have
failed to produce an explosion. Here we report a simulation of the merger of
two equal-mass white dwarfs that leads to an underluminous explosion, though at
the expense of requiring a single common-envelope phase, and component masses
of ~0.9 M_sun. The light curve is too broad, but the synthesized spectra, red
colour and low expansion velocities are all close to what is observed for
sub-luminous 1991bg-like events. While mass ratios can be slightly less than
one and still produce an underluminous event, the masses have to be in the
range 0.83-0.9 M_sun.Comment: Accepted to Natur
White dwarf deflagrations for Type Iax supernovae: polarisation signatures from the explosion and companion interaction
Growing evidence suggests that Type Iax supernovae might be the result of thermonuclear deflagrations of Chandrasekhar-mass white dwarfs in binary systems. We carry out Monte Carlo radiative transfer simulations and predict spectropolarimetric features originating from the supernova explosion and subsequent ejecta interaction with the companion star. Specifically, we calculate viewing-angle dependent flux and polarisation spectra for a 3D model simulating the deflagration of a Chandrasekhar-mass white dwarf and, for a second model, simulating the ejecta interaction with a main-sequence star. We find that the intrinsic signal is weakly polarised and only mildly viewing-angle dependent, owing to the overall spherical symmetry of the explosion and the depolarising contribution of iron-group elements dominating the ejecta composition. The interaction with the companion star carves out a cavity in the ejecta and produces a detectable, but modest signal that is significant only at relatively blue wavelengths (5000 Å). In particular, increasingly fainter and redder spectra are predicted for observer orientations further from the cavity, while a modest polarisation signal P∼0.2 per cent is found at blue wavelengths for orientations 30◦ and 45◦ away from the cavity. We find a reasonable agreement between the interaction model viewed from these orientations and spectropolarimetric data of SN 2005hk and interpret the maximum-light polarisation signal seen at blue wavelengths for this event as a possible signature of the ejecta–companion interaction. We encourage further polarimetric observations of SNe Iax to test whether our results can be extended and generalised to the whole SN Iax class
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