A Super-Solar Metallicity for the Progenitor of Kepler's Supernova. (arXiv:1302.5435v2 [astro-ph.HE] UPDATED):
We have performed deep X-ray observations of the remnant of Kepler's
supernova (SN 1604) as a Key Project of the Suzaku Observatory. Our main goal
is to detect secondary Fe-peak elements in the SN ejecta to gain insights into
the Type Ia supernova explosion mechanism and the nature of the progenitor.
Here we report our initial results. We made a conclusive detection of X-ray
emission lines from highly ionized Mn, Cr, and Ni as well as Fe. The observed
Mn-to-Cr line flux ratio is ~0.60, ~30% larger than that measured in Tycho's
remnant. We estimate a Mn-to-Cr mass ratio of ~0.77, which is strongly
suggestive of a large neutron excess in the progenitor star before the onset of
the thermonuclear runaway. The observed Ni-to-Fe line flux ratio (~0.03)
corresponds to a mass ratio of ~0.06, which is generally consistent with the
products of explosive Si-burning regime in Type Ia explosion models, and rules
out contamination from the products of neutron-rich nuclear statistical
equilibrium in the shocked ejecta. Together with the previously suggested
luminous nature of the explosion, these mass ratios provide strong evidence for
a super-solar metallicity in the SN progenitor (~3 Z_sun). Kepler's supernova
was likely the thermonuclear explosion of a white dwarf formed in the recent
past that must have exploded through a relatively prompt channel.
Showing posts with label SNIa. Show all posts
Showing posts with label SNIa. Show all posts
Saturday, March 9, 2013
RX J0648.0--4418: the fastest-spinning white dwarf. (arXiv:1302.4634v1 [astro-ph.HE])
RX J0648.0--4418: the fastest-spinning white dwarf. (arXiv:1302.4634v1 [astro-ph.HE]):
RX J0648.0-4418 is a post common-envelope X-ray binary composed of a hot
subdwarf and one of the most massive white dwarfs with a dynamical mass
measurement (1.28+/-0.05 M_sun). This white dwarf, with a spin period of 13.2
s, rotates more than twice faster than the white dwarf in the cataclysmic
variable AE Aqr. The current properties of these two binaries, as well as their
future evolution, are quite different, despite both contain a fast-spinning
white dwarf. RX J0648.0-4418 could be the progenitor of either a Type Ia
supernova or of a non-recycled millisecond pulsars.
RX J0648.0-4418 is a post common-envelope X-ray binary composed of a hot
subdwarf and one of the most massive white dwarfs with a dynamical mass
measurement (1.28+/-0.05 M_sun). This white dwarf, with a spin period of 13.2
s, rotates more than twice faster than the white dwarf in the cataclysmic
variable AE Aqr. The current properties of these two binaries, as well as their
future evolution, are quite different, despite both contain a fast-spinning
white dwarf. RX J0648.0-4418 could be the progenitor of either a Type Ia
supernova or of a non-recycled millisecond pulsars.
Sunday, March 3, 2013
Conditions For Successful Helium Detonations In Astrophysical Environments. (arXiv:1302.6235v1 [astro-ph.HE])
Conditions For Successful Helium Detonations In Astrophysical Environments. (arXiv:1302.6235v1 [astro-ph.HE]):
Several models for type Ia-like supernovae events rely on the production of a
self-sustained detonation powered by nuclear reactions.In the absence of
hydrogen, the fuel that powers these detonations typically consists of either
pure helium (He) or a mixture of carbon and oxygen (C/O). Studies that
systematically determine the conditions required to initiate detonations in C/O
material exist, but until now no analogous investigation of degenerate He
matter has been conducted. We perform one-dimensional reactive hydrodynamical
simulations at a variety of initial density and temperature combinations and
find critical length scales for the initiation of He detonations that range
between 1 -- $10^{10}$ cm. These sizes are consistently smaller than the
corresponding Chapman-Jouguet (CJ) length scales by a factor of ~100, providing
opportunities for thermonuclear explosions in a wider range of low mass white
dwarfs (WDs) than previously thought possible. We find that virialized WDs with
as little mass as 0.24 $M_\odot$ can be detonated, and that even less massive
WDs can be detonated if a sizable fraction of their mass is raised to a higher
adiabat. That the initiation length is exceeded by the CJ length implies that
certain systems may not reach nuclear statistical equilibrium within the time
it takes a detonation to traverse the object. In support of this hypothesis, we
demonstrate that incomplete burning will occur in the majority of He WD
detonations and that $^{44}$Ti, rather than $^{56}$Ni, is the predominant
burning product for many of these events. We anticipate that a measure of the
quantity of $^{44}$Ti and $^{56}$Ni produced in a helium-rich thermonuclear
explosion can potentially be used to constrain the nature of the progenitor
system.
Several models for type Ia-like supernovae events rely on the production of a
self-sustained detonation powered by nuclear reactions.In the absence of
hydrogen, the fuel that powers these detonations typically consists of either
pure helium (He) or a mixture of carbon and oxygen (C/O). Studies that
systematically determine the conditions required to initiate detonations in C/O
material exist, but until now no analogous investigation of degenerate He
matter has been conducted. We perform one-dimensional reactive hydrodynamical
simulations at a variety of initial density and temperature combinations and
find critical length scales for the initiation of He detonations that range
between 1 -- $10^{10}$ cm. These sizes are consistently smaller than the
corresponding Chapman-Jouguet (CJ) length scales by a factor of ~100, providing
opportunities for thermonuclear explosions in a wider range of low mass white
dwarfs (WDs) than previously thought possible. We find that virialized WDs with
as little mass as 0.24 $M_\odot$ can be detonated, and that even less massive
WDs can be detonated if a sizable fraction of their mass is raised to a higher
adiabat. That the initiation length is exceeded by the CJ length implies that
certain systems may not reach nuclear statistical equilibrium within the time
it takes a detonation to traverse the object. In support of this hypothesis, we
demonstrate that incomplete burning will occur in the majority of He WD
detonations and that $^{44}$Ti, rather than $^{56}$Ni, is the predominant
burning product for many of these events. We anticipate that a measure of the
quantity of $^{44}$Ti and $^{56}$Ni produced in a helium-rich thermonuclear
explosion can potentially be used to constrain the nature of the progenitor
system.
Wednesday, December 12, 2012
Insights into thermonuclear supernovae from the incomplete silicon burning process. (arXiv:1212.2410v1 [astro-ph.SR])
Insights into thermonuclear supernovae from the incomplete silicon burning process. (arXiv:1212.2410v1 [astro-ph.SR]):
Type Ia supernova (SNIa) explosions synthesize a few tenths to several tenths
of a solar mass, whose composition is the result of incomplete silicon burning
that reaches peak temperatures of 4 GK to 5 GK. The elemental abundances are
sensitive to the physical conditions in the explosion, making their measurement
a promising clue to uncovering the properties of the progenitor star and of the
explosion itself. Using a parameterized description of the thermodynamic
history of matter undergoing incomplete silicon burning, we computed the final
composition for a range of parameters wide enough to encompass current models
of SNIa. Then, we searched for combinations of elemental abundances that trace
the parameters values and are potentially measurable. For this purpose, we
divide the present study into two epochs of SNIa, namely the optical epoch,
from a few weeks to several months after the explosion, and the X-ray epoch,
which refers to the time period in which the supernova remnant is young,
starting one or two hundred years age and ending a thousand years after the
event. During the optical epoch, the only SNIa property that can be extracted
from the detection of incomplete silicon burning elements is the neutron excess
of the progenitor white dwarf at thermal runaway, which can be determined
through measuring the ratio of the abundance of manganese to that of titanium,
chromium, or vanadium. Conversely, in the X-ray epoch, any abundance ratio
built using a couple of elements from titanium, vanadium, chromium, or
manganese may constrain the initial neutron excess. Furthermore, measuring the
ratio of the abundances of vanadium to manganese in the X-ray might shed light
on the timescale of the thermonuclear explosion.
Type Ia supernova (SNIa) explosions synthesize a few tenths to several tenths
of a solar mass, whose composition is the result of incomplete silicon burning
that reaches peak temperatures of 4 GK to 5 GK. The elemental abundances are
sensitive to the physical conditions in the explosion, making their measurement
a promising clue to uncovering the properties of the progenitor star and of the
explosion itself. Using a parameterized description of the thermodynamic
history of matter undergoing incomplete silicon burning, we computed the final
composition for a range of parameters wide enough to encompass current models
of SNIa. Then, we searched for combinations of elemental abundances that trace
the parameters values and are potentially measurable. For this purpose, we
divide the present study into two epochs of SNIa, namely the optical epoch,
from a few weeks to several months after the explosion, and the X-ray epoch,
which refers to the time period in which the supernova remnant is young,
starting one or two hundred years age and ending a thousand years after the
event. During the optical epoch, the only SNIa property that can be extracted
from the detection of incomplete silicon burning elements is the neutron excess
of the progenitor white dwarf at thermal runaway, which can be determined
through measuring the ratio of the abundance of manganese to that of titanium,
chromium, or vanadium. Conversely, in the X-ray epoch, any abundance ratio
built using a couple of elements from titanium, vanadium, chromium, or
manganese may constrain the initial neutron excess. Furthermore, measuring the
ratio of the abundances of vanadium to manganese in the X-ray might shed light
on the timescale of the thermonuclear explosion.
Recurrent novae as progenitors of Type Ia supernovae. (arXiv:1212.2295v1 [astro-ph.SR])
Recurrent novae as progenitors of Type Ia supernovae. (arXiv:1212.2295v1 [astro-ph.SR]):
Recurrent novae are binaries harboring a very massive white dwarf (WD), as
massive as the Chandrasekhar mass, because of their short recurrence periods of
nova outbursts of 10-100 years. Thus, recurrent novae are considered as
candidates of progenitors of Type Ia supernovae (SNe Ia). In fact, the SN Ia
PTF11kx showed evidence that its progenitor is a symbiotic recurrent nova. The
binary parameters of recurrent novae have been well determined, especially for
the ones with frequent outbursts, U Sco and RS Oph, which provide useful
information on the elementary processes in binary evolution toward SNe Ia.
Therefore we use them as testbeds for binary evolution models. For example, the
original double degenerate (DD) scenario cannot reproduce RS Oph type recurrent
novae, whereas the new single degenerate (SD) scenario proposed by Hachisu et
al. (1999) naturally can. We review main differences between the SD and DD
scenarios, especially for their basic processes of binary evolution. We also
discuss observational support for each physical process. The original DD
scenario is based on the physics in 1980s, whereas the SD scenario on more
recent physics including the new opacity, mass-growth efficiency of WDs, and
optically thick winds developed in nova outbursts.
Recurrent novae are binaries harboring a very massive white dwarf (WD), as
massive as the Chandrasekhar mass, because of their short recurrence periods of
nova outbursts of 10-100 years. Thus, recurrent novae are considered as
candidates of progenitors of Type Ia supernovae (SNe Ia). In fact, the SN Ia
PTF11kx showed evidence that its progenitor is a symbiotic recurrent nova. The
binary parameters of recurrent novae have been well determined, especially for
the ones with frequent outbursts, U Sco and RS Oph, which provide useful
information on the elementary processes in binary evolution toward SNe Ia.
Therefore we use them as testbeds for binary evolution models. For example, the
original double degenerate (DD) scenario cannot reproduce RS Oph type recurrent
novae, whereas the new single degenerate (SD) scenario proposed by Hachisu et
al. (1999) naturally can. We review main differences between the SD and DD
scenarios, especially for their basic processes of binary evolution. We also
discuss observational support for each physical process. The original DD
scenario is based on the physics in 1980s, whereas the SD scenario on more
recent physics including the new opacity, mass-growth efficiency of WDs, and
optically thick winds developed in nova outbursts.
Saturday, December 1, 2012
Three-dimensional delayed-detonation models with nucleosynthesis for Type Ia supernovae. (arXiv:1211.3015v1 [astro-ph.SR])
Three-dimensional delayed-detonation models with nucleosynthesis for Type Ia supernovae. (arXiv:1211.3015v1 [astro-ph.SR]):
We present results for a suite of fourteen three-dimensional, high resolution
hydrodynamical simulations of delayed-detonation modelsof Type Ia supernova (SN
Ia) explosions. This model suite comprises the first set of three-dimensional
SN Ia simulations with detailed isotopic yield information. As such, it may
serve as a database for Chandrasekhar-mass delayed-detonation model
nucleosynthetic yields and for deriving synthetic observables such as spectra
and light curves. We employ a physically motivated, stochastic model based on
turbulent velocity fluctuations and fuel density to calculate in situ the
deflagration to detonation transition (DDT) probabilities. To obtain different
strengths of the deflagration phase and thereby different degrees of
pre-expansion, we have chosen a sequence of initial models with 1, 3, 5, 10,
20, 40, 100, 150, 200, 300, and 1600 (two different realizations) ignition
kernels in a hydrostatic white dwarf with central density of 2.9 x 10^9 gcc,
plus in addition one high central density (5.5 x 10^9 gcc), and one low central
density (1.0 x 10^9 gcc) rendition of the 100 ignition kernel configuration.
For each simulation we determined detailed nucleosynthetic yields by
post-processing 10^6 tracer particles with a 384 nuclide reaction network. All
delayed detonation models result in explosions unbinding the white dwarf,
producing a range of 56Ni masses from 0.32 to 1.11 solar masses. As a general
trend, the models predict that the stable neutron-rich iron group isotopes are
not found at the lowest velocities, but rather at intermediate velocities
(~3,000 - 10,000 km/s) in a shell surrounding a 56Ni-rich core. The models
further predict relatively low velocity oxygen and carbon, with typical minimum
velocities around 4,000 and 10,000 km/s, respectively.
We present results for a suite of fourteen three-dimensional, high resolution
hydrodynamical simulations of delayed-detonation modelsof Type Ia supernova (SN
Ia) explosions. This model suite comprises the first set of three-dimensional
SN Ia simulations with detailed isotopic yield information. As such, it may
serve as a database for Chandrasekhar-mass delayed-detonation model
nucleosynthetic yields and for deriving synthetic observables such as spectra
and light curves. We employ a physically motivated, stochastic model based on
turbulent velocity fluctuations and fuel density to calculate in situ the
deflagration to detonation transition (DDT) probabilities. To obtain different
strengths of the deflagration phase and thereby different degrees of
pre-expansion, we have chosen a sequence of initial models with 1, 3, 5, 10,
20, 40, 100, 150, 200, 300, and 1600 (two different realizations) ignition
kernels in a hydrostatic white dwarf with central density of 2.9 x 10^9 gcc,
plus in addition one high central density (5.5 x 10^9 gcc), and one low central
density (1.0 x 10^9 gcc) rendition of the 100 ignition kernel configuration.
For each simulation we determined detailed nucleosynthetic yields by
post-processing 10^6 tracer particles with a 384 nuclide reaction network. All
delayed detonation models result in explosions unbinding the white dwarf,
producing a range of 56Ni masses from 0.32 to 1.11 solar masses. As a general
trend, the models predict that the stable neutron-rich iron group isotopes are
not found at the lowest velocities, but rather at intermediate velocities
(~3,000 - 10,000 km/s) in a shell surrounding a 56Ni-rich core. The models
further predict relatively low velocity oxygen and carbon, with typical minimum
velocities around 4,000 and 10,000 km/s, respectively.
Hydrodynamic Studies of the Evolution of Recurrent, Symbiotic, and Dwarf Novae: The White Dwarf Components are Growing in Mass. (arXiv:1211.6145v1 [astro-ph.SR])
Hydrodynamic Studies of the Evolution of Recurrent, Symbiotic, and Dwarf Novae: The White Dwarf Components are Growing in Mass. (arXiv:1211.6145v1 [astro-ph.SR]):
Symbiotic binaries are systems containing white dwarfs (WDs) and red giants.
Symbiotic novae are those systems in which thermonuclear eruptions occur on the
WD components. These are to be distinguished from events driven by accretion
disk instabilities analogous to dwarf novae eruptions in cataclysmic variable
outbursts. Another class of symbiotic systems are those in which the WD is
extremely luminous and it seems likely that quiescent nuclear burning is
ongoing on the accreting WD. A fundamental question is the secular evolution of
the WD. Do the repeated outbursts or quiescent burning in these accreting
systems cause the WD to gain or lose mass? If it is gaining mass, can it
eventually reach the Chandrasekhar Limit and become a supernova (a SN Ia if it
can hide the hydrogen and helium in the system)? In order to better understand
these systems, we have begun a new study of the evolution of Thermonuclear
Runaways (TNRs) in the accreted envelopes of WDs using a variety of initial WD
masses, luminosities and mass accretion rates. We use our 1-D hydro code, NOVA,
which includes the new convective algorithm of Arnett, Meakin and Young, the
Hix and Thielemann nuclear reaction solver, the Iliadis reaction rate library,
the Timmes equation of state, and the OPAL opacities. We assume a solar
composition (Lodders abundance distribution) and do not allow any mixing of
accreted material with core material. This assumption strongly influences our
results. We report here (1) that the WD grows in mass for all simulations so
that canonical `steady burning' does not occur, and (2) that only a small
fraction of the accreted matter is ejected in some (but not all) simulations.
We also find that the accreting systems, before thermonuclear runaway, are too
cool to be seen in X-ray searches for SN Ia progenitors.
Symbiotic binaries are systems containing white dwarfs (WDs) and red giants.
Symbiotic novae are those systems in which thermonuclear eruptions occur on the
WD components. These are to be distinguished from events driven by accretion
disk instabilities analogous to dwarf novae eruptions in cataclysmic variable
outbursts. Another class of symbiotic systems are those in which the WD is
extremely luminous and it seems likely that quiescent nuclear burning is
ongoing on the accreting WD. A fundamental question is the secular evolution of
the WD. Do the repeated outbursts or quiescent burning in these accreting
systems cause the WD to gain or lose mass? If it is gaining mass, can it
eventually reach the Chandrasekhar Limit and become a supernova (a SN Ia if it
can hide the hydrogen and helium in the system)? In order to better understand
these systems, we have begun a new study of the evolution of Thermonuclear
Runaways (TNRs) in the accreted envelopes of WDs using a variety of initial WD
masses, luminosities and mass accretion rates. We use our 1-D hydro code, NOVA,
which includes the new convective algorithm of Arnett, Meakin and Young, the
Hix and Thielemann nuclear reaction solver, the Iliadis reaction rate library,
the Timmes equation of state, and the OPAL opacities. We assume a solar
composition (Lodders abundance distribution) and do not allow any mixing of
accreted material with core material. This assumption strongly influences our
results. We report here (1) that the WD grows in mass for all simulations so
that canonical `steady burning' does not occur, and (2) that only a small
fraction of the accreted matter is ejected in some (but not all) simulations.
We also find that the accreting systems, before thermonuclear runaway, are too
cool to be seen in X-ray searches for SN Ia progenitors.
Friday, November 9, 2012
Three-dimensional numerical investigations of the morphology of type Ia SNRs. (arXiv:1210.7790v1 [astro-ph.GA])
Three-dimensional numerical investigations of the morphology of type Ia SNRs. (arXiv:1210.7790v1 [astro-ph.GA]):
We explore the morphology of Type Ia supernova remnants (SNRs) using
three-dimensional hydrodynamics modeling and an exponential density profile.
Our model distinguishes ejecta from the interstellar medium (ISM), and tracks
the ionization age of shocked ejecta, both of which allow for additional
analysis of the simulated remnants. We also include the adiabatic index as a
free parameter, which affects the compressibility of the fluid and emulates the
efficiency of cosmic ray acceleration by shock fronts. In addition to
generating 3-D images of the simulations, we compute line-of-sight projections
through the remnants for comparison against observations of Tycho's SNR and SN
1006. We find that several features observed in these two remnants, such as the
separation between the fluid discontinuities and the presence of ejecta knots
ahead of the forward shock, can be generated by smooth ejecta without any
initial clumpiness. Our results are consistent with SN 1006 being dynamically
younger than Tycho's SNR, and more efficiently accelerating cosmic rays at its
forward shock. We conclude that clumpiness is not a necessary condition to
reproduce many observed features of Type Ia supernova remnants, particularly
the radial profiles and the fleecy emission from ejecta at the central region
of both remnants.
We explore the morphology of Type Ia supernova remnants (SNRs) using
three-dimensional hydrodynamics modeling and an exponential density profile.
Our model distinguishes ejecta from the interstellar medium (ISM), and tracks
the ionization age of shocked ejecta, both of which allow for additional
analysis of the simulated remnants. We also include the adiabatic index as a
free parameter, which affects the compressibility of the fluid and emulates the
efficiency of cosmic ray acceleration by shock fronts. In addition to
generating 3-D images of the simulations, we compute line-of-sight projections
through the remnants for comparison against observations of Tycho's SNR and SN
1006. We find that several features observed in these two remnants, such as the
separation between the fluid discontinuities and the presence of ejecta knots
ahead of the forward shock, can be generated by smooth ejecta without any
initial clumpiness. Our results are consistent with SN 1006 being dynamically
younger than Tycho's SNR, and more efficiently accelerating cosmic rays at its
forward shock. We conclude that clumpiness is not a necessary condition to
reproduce many observed features of Type Ia supernova remnants, particularly
the radial profiles and the fleecy emission from ejecta at the central region
of both remnants.
Thursday, October 25, 2012
Theoretical Studies of Accretion of Matter onto White Dwarfs and the Single Degenerate Scenario for Supernovae of Type Ia. (arXiv:1210.6086v1 [astro-ph.SR])
Theoretical Studies of Accretion of Matter onto White Dwarfs and the Single Degenerate Scenario for Supernovae of Type Ia. (arXiv:1210.6086v1 [astro-ph.SR]):
We present a brief summary of the Single Degenerate Scenario for the
progenitors of Type Ia Supernovae in which it is assumed that a low mass
carbon-oxygen white dwarf is growing in mass as a result of accretion from a
secondary star in a close binary system. Recent hydrodynamic simulations of
accretion of solar material onto white dwarfs without mixing always produce a
thermonuclear runaway and steady burning does not occur. For a broad range in
WD mass (0.4 Solar masses to 1.35 Solar Masses), the maximum ejected material
occurs for the 1.25 Solar Mass sequences and then decreases as the white dwarf
mass decreases. Therefore, the white dwarfs are growing in mass as a
consequence of the accretion of solar material and as long as there is no
mixing of accreted material with core material. In contrast, a thermonuclear
runaway in the accreted hydrogen-rich layers on the low luminosity WDs in close
binary systems where mixing of core matter with accreted material has occurred
is the outburst mechanism for Classical, Recurrent, and Symbiotic novae. The
differences in characteristics of these systems is likely the WD mass and mass
accretion rate. The high levels of enrichment of CN ejecta in elements ranging
from carbon to sulfur confirm that there is dredge-up of matter from the core
of the WD and enable them to contribute to the chemical enrichment of the
interstellar medium. Therefore, studies of CNe can lead to an improved
understanding of Galactic nucleosynthesis, some sources of pre-solar grains,
and the Extragalactic distance scale. The characteristics of the outburst
depend on the white dwarf mass, luminosity, mass accretion rate, and the
chemical composition of both the accreting material and WD material. The
properties of the outburst also depends on when, how, and if the accreted
layers are mixed with the WD core and the mixing mechanism is still unknown.
We present a brief summary of the Single Degenerate Scenario for the
progenitors of Type Ia Supernovae in which it is assumed that a low mass
carbon-oxygen white dwarf is growing in mass as a result of accretion from a
secondary star in a close binary system. Recent hydrodynamic simulations of
accretion of solar material onto white dwarfs without mixing always produce a
thermonuclear runaway and steady burning does not occur. For a broad range in
WD mass (0.4 Solar masses to 1.35 Solar Masses), the maximum ejected material
occurs for the 1.25 Solar Mass sequences and then decreases as the white dwarf
mass decreases. Therefore, the white dwarfs are growing in mass as a
consequence of the accretion of solar material and as long as there is no
mixing of accreted material with core material. In contrast, a thermonuclear
runaway in the accreted hydrogen-rich layers on the low luminosity WDs in close
binary systems where mixing of core matter with accreted material has occurred
is the outburst mechanism for Classical, Recurrent, and Symbiotic novae. The
differences in characteristics of these systems is likely the WD mass and mass
accretion rate. The high levels of enrichment of CN ejecta in elements ranging
from carbon to sulfur confirm that there is dredge-up of matter from the core
of the WD and enable them to contribute to the chemical enrichment of the
interstellar medium. Therefore, studies of CNe can lead to an improved
understanding of Galactic nucleosynthesis, some sources of pre-solar grains,
and the Extragalactic distance scale. The characteristics of the outburst
depend on the white dwarf mass, luminosity, mass accretion rate, and the
chemical composition of both the accreting material and WD material. The
properties of the outburst also depends on when, how, and if the accreted
layers are mixed with the WD core and the mixing mechanism is still unknown.
Tuesday, October 9, 2012
No surviving evolved companions to the progenitor of supernova SN 1006. (arXiv:1210.1948v1 [astro-ph.GA])
No surviving evolved companions to the progenitor of supernova SN 1006. (arXiv:1210.1948v1 [astro-ph.GA]):
Type Ia supernovae are thought to occur as a white dwarf made of carbon and
oxygen accretes sufficient mass to trigger a thermonuclear explosion$^{1}$. The
accretion could occur slowly from an unevolved (main-sequence) or evolved
(subgiant or giant) star$^{2,3}$, that being dubbed the single-degenerate
channel, or rapidly as it breaks up a smaller orbiting white dwarf (the double-
degenerate channel)$^{3,4}$. Obviously, a companion will survive the explosion
only in the single-degenerate channel$^{5}$. Both channels might contribute to
the production of type Ia supernovae$^{6,7}$ but their relative proportions
still remain a fundamental puzzle in astronomy. Previous searches for remnant
companions have revealed one possible case for SN 1572$^{8,9}$, though that has
been criticized$^{10}$. More recently, observations have restricted surviving
companions to be small, main-sequence stars$^{11,12,13}$, ruling out giant
companions, though still allowing the single-degenerate channel. Here we report
the result of a search for surviving companions to the progenitor of SN
1006$^{14}$. None of the stars within 4' of the apparent site of the explosion
is associated with the supernova remnant, so we can firmly exclude all giant
and subgiant companions to the progenitor. Combined with the previous results,
less than 20 per cent of type Iae occur through the single degenerate channel.
Type Ia supernovae are thought to occur as a white dwarf made of carbon and
oxygen accretes sufficient mass to trigger a thermonuclear explosion$^{1}$. The
accretion could occur slowly from an unevolved (main-sequence) or evolved
(subgiant or giant) star$^{2,3}$, that being dubbed the single-degenerate
channel, or rapidly as it breaks up a smaller orbiting white dwarf (the double-
degenerate channel)$^{3,4}$. Obviously, a companion will survive the explosion
only in the single-degenerate channel$^{5}$. Both channels might contribute to
the production of type Ia supernovae$^{6,7}$ but their relative proportions
still remain a fundamental puzzle in astronomy. Previous searches for remnant
companions have revealed one possible case for SN 1572$^{8,9}$, though that has
been criticized$^{10}$. More recently, observations have restricted surviving
companions to be small, main-sequence stars$^{11,12,13}$, ruling out giant
companions, though still allowing the single-degenerate channel. Here we report
the result of a search for surviving companions to the progenitor of SN
1006$^{14}$. None of the stars within 4' of the apparent site of the explosion
is associated with the supernova remnant, so we can firmly exclude all giant
and subgiant companions to the progenitor. Combined with the previous results,
less than 20 per cent of type Iae occur through the single degenerate channel.
Monday, September 10, 2012
Binary Paths to Type Ia Supernovae Explosions: The Highlights. (arXiv:1209.1201v1 [astro-ph.CO])
Binary Paths to Type Ia Supernovae Explosions: The Highlights. (arXiv:1209.1201v1 [astro-ph.CO]):
This Symposium was focused on the hunt for the progenitors of Supernovae of
Type Ia. Is there a main channel for the production of SNeIa? If so, are these
elusive progenitors Single Degenerate or Double Degenerate systems? Although
most participants seemed to favour the Single Degenerate channel, there was no
general agreement on the type of binary system at play. An observational puzzle
that was highlighted was the apparent paucity of Super-Soft Sources in our
Galaxy and also in external galaxies. The Single Degenerate channel (and as it
was pointed out, quite possibly also the Double Degenerate channel) requires
the binary system to pass through a phase of steady nuclear burning. However,
the observed number of Super-Soft sources falls short by a factor of up to 100
in explaining the estimated birth rates of SNeIa. Thus, are these Super-Soft
sources somehow hidden away and radiating at different wavelengths or are we
missing some important pieces of this puzzle that may lead to the elimination
of a certain class of progenitor? Another unanswered question concerns the
dependence of SNeIa luminosities on the age of their host galaxy. Several
hypotheses were put forward, but none was singled out as the most likely
explanation.
It is fair to say that at the end of the Symposium the definitive answer to
the vexed progenitor question remained is well and truly wide open.
This Symposium was focused on the hunt for the progenitors of Supernovae of
Type Ia. Is there a main channel for the production of SNeIa? If so, are these
elusive progenitors Single Degenerate or Double Degenerate systems? Although
most participants seemed to favour the Single Degenerate channel, there was no
general agreement on the type of binary system at play. An observational puzzle
that was highlighted was the apparent paucity of Super-Soft Sources in our
Galaxy and also in external galaxies. The Single Degenerate channel (and as it
was pointed out, quite possibly also the Double Degenerate channel) requires
the binary system to pass through a phase of steady nuclear burning. However,
the observed number of Super-Soft sources falls short by a factor of up to 100
in explaining the estimated birth rates of SNeIa. Thus, are these Super-Soft
sources somehow hidden away and radiating at different wavelengths or are we
missing some important pieces of this puzzle that may lead to the elimination
of a certain class of progenitor? Another unanswered question concerns the
dependence of SNeIa luminosities on the age of their host galaxy. Several
hypotheses were put forward, but none was singled out as the most likely
explanation.
It is fair to say that at the end of the Symposium the definitive answer to
the vexed progenitor question remained is well and truly wide open.
Thursday, September 6, 2012
White Dwarf/M Dwarf Binaries as Single Degenerate Progenitors of Type Ia Supernovae. (arXiv:1209.1021v1 [astro-ph.SR])
White Dwarf/M Dwarf Binaries as Single Degenerate Progenitors of Type Ia Supernovae. (arXiv:1209.1021v1 [astro-ph.SR]):
Limits on the companions of white dwarfs in the single degenerate scenario
for the origin of Type Ia supernovae (SNIa) have gotten increasingly tight. The
only type of non-degenerate stars that survive the limits on the companions of
SNIa in SNR 0509-67.5 and SN1572 are M dwarfs. M dwarfs have special properties
that have not been considered in most work on the progenitors of SNIa: they
have small but finite magnetic fields, and they flare frequently. These
properties are explored in the context of SNIa progenitors. White dwarf/M dwarf
pairs may be sufficiently plentiful to provide an adequate rate of explosions.
Even modest magnetic fields on the white dwarf and M dwarf will yield adequate
torques to lock the two stars together, resulting in a slowly rotating white
dwarf, with the magnetic poles pointing at one another in the orbital plane.
The mass loss will be channeled by a "magnetic bottle" connecting the two
stars, landing on a concentrated polar area on the white dwarf. This enhances
the effective rate of accretion compared to spherical accretion. Luminosity
from accretion and hydrogen burning on the surface of the white dwarf may
induce self-excited mass transfer. The combined effects of self-excited mass
loss, polar accretion, and magnetic inhibition of mixing of accretion layers
give possible means to beat the "nova limit" and grow the white dwarf to the
Chandrasekhar mass even at rather moderate mass accretion rates.
Limits on the companions of white dwarfs in the single degenerate scenario
for the origin of Type Ia supernovae (SNIa) have gotten increasingly tight. The
only type of non-degenerate stars that survive the limits on the companions of
SNIa in SNR 0509-67.5 and SN1572 are M dwarfs. M dwarfs have special properties
that have not been considered in most work on the progenitors of SNIa: they
have small but finite magnetic fields, and they flare frequently. These
properties are explored in the context of SNIa progenitors. White dwarf/M dwarf
pairs may be sufficiently plentiful to provide an adequate rate of explosions.
Even modest magnetic fields on the white dwarf and M dwarf will yield adequate
torques to lock the two stars together, resulting in a slowly rotating white
dwarf, with the magnetic poles pointing at one another in the orbital plane.
The mass loss will be channeled by a "magnetic bottle" connecting the two
stars, landing on a concentrated polar area on the white dwarf. This enhances
the effective rate of accretion compared to spherical accretion. Luminosity
from accretion and hydrogen burning on the surface of the white dwarf may
induce self-excited mass transfer. The combined effects of self-excited mass
loss, polar accretion, and magnetic inhibition of mixing of accretion layers
give possible means to beat the "nova limit" and grow the white dwarf to the
Chandrasekhar mass even at rather moderate mass accretion rates.
Tuesday, September 4, 2012
Discovery of 100 supernovae among 700,000 Sloan spectra: the Type-Ia supernova rate versus galaxy mass and star-formation rate at redshift ~0.1. (arXiv:1209.0008v1 [astro-ph.CO])
Discovery of 100 supernovae among 700,000 Sloan spectra: the Type-Ia supernova rate versus galaxy mass and star-formation rate at redshift ~0.1. (arXiv:1209.0008v1 [astro-ph.CO]):
Using a method to discover and classify supernovae (SNe) in galaxy spectra,
we find 90 Type Ia SNe (SNe Ia) and 10 Type IIP SNe among the ~700,000 galaxy
spectra in the Sloan Digital Sky Survey Data Release 7 that have VESPA-derived
star-formation histories (SFHs). We use the SN Ia sample to measure SN Ia rates
per unit stellar mass. We confirm, at the median redshift of the sample, z =
0.1, the inverse dependence on galaxy mass of the SN Ia rate per unit mass,
previously reported by Li et al. (2011b) for a local sample. We further
confirm, following Kistler et al. (2011), that this relation can be explained
by the combination of galaxy "downsizing" and a power-law delay-time
distribution (DTD; the distribution of times that elapse between a hypothetical
burst of star formation and the subsequent SN Ia explosions) with an index of
-1, inherent to the double-degenerate progenitor scenario. We use the method of
Maoz et al. (2011) to recover the DTD by comparing the number of SNe Ia hosted
by each galaxy in our sample with the VESPA-derived SFH of the stellar
population within the spectral aperture. In this galaxy sample, which is
dominated by old and massive galaxies, we recover a "delayed" component to the
DTD of 4.5 +/- 0.6 X 10^-14 SNe Msun^-1 yr^-1 for delays in the range > 2.4
Gyr. The mass-normalized SN Ia rate, averaged over all masses and redshifts in
our galaxy sample, is R(Ia,M,z=0.1) = 0.10 +/- 0.01 SNuM, and the volumetric
rate is R(Ia,V,z=0.1) = 0.25 +/- 0.03 X 10^-4 SNe yr^-1 Mpc^-3. This is the
most precise SN Ia rate measurement at this redshift, and is consistent with
rates and the rate evolution from other SN Ia surveys.
Using a method to discover and classify supernovae (SNe) in galaxy spectra,
we find 90 Type Ia SNe (SNe Ia) and 10 Type IIP SNe among the ~700,000 galaxy
spectra in the Sloan Digital Sky Survey Data Release 7 that have VESPA-derived
star-formation histories (SFHs). We use the SN Ia sample to measure SN Ia rates
per unit stellar mass. We confirm, at the median redshift of the sample, z =
0.1, the inverse dependence on galaxy mass of the SN Ia rate per unit mass,
previously reported by Li et al. (2011b) for a local sample. We further
confirm, following Kistler et al. (2011), that this relation can be explained
by the combination of galaxy "downsizing" and a power-law delay-time
distribution (DTD; the distribution of times that elapse between a hypothetical
burst of star formation and the subsequent SN Ia explosions) with an index of
-1, inherent to the double-degenerate progenitor scenario. We use the method of
Maoz et al. (2011) to recover the DTD by comparing the number of SNe Ia hosted
by each galaxy in our sample with the VESPA-derived SFH of the stellar
population within the spectral aperture. In this galaxy sample, which is
dominated by old and massive galaxies, we recover a "delayed" component to the
DTD of 4.5 +/- 0.6 X 10^-14 SNe Msun^-1 yr^-1 for delays in the range > 2.4
Gyr. The mass-normalized SN Ia rate, averaged over all masses and redshifts in
our galaxy sample, is R(Ia,M,z=0.1) = 0.10 +/- 0.01 SNuM, and the volumetric
rate is R(Ia,V,z=0.1) = 0.25 +/- 0.03 X 10^-4 SNe yr^-1 Mpc^-3. This is the
most precise SN Ia rate measurement at this redshift, and is consistent with
rates and the rate evolution from other SN Ia surveys.
Friday, August 17, 2012
Prospect of Studying Hard X- and Gamma-Rays from Type Ia Supernovae. (arXiv:1208.2094v1 [astro-ph.HE])
Prospect of Studying Hard X- and Gamma-Rays from Type Ia Supernovae. (arXiv:1208.2094v1 [astro-ph.HE]):
We perform multi-dimensional, time-dependent radiation transfer simulations
for hard X-ray and $\gamma$-ray emissions, following radioactive decays of
$^{56}$Ni and $^{56}$Co, 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 with an exposure 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 the upper limit for the mass of
$^{56}$Ni as $\lsim$1.0 M_{\odot}$ 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 or ASTRO-H, launched in 2012 and to be
so in 2014, will reach to SNe Ia at $\sim$15 Mpc, i.e., one SN in a 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
$\sim$25 Mpc, i.e., a few SNe Ia per year. Proposed next generation
$\gamma$-ray missions, e.g., GRIPS, could reach to SNe Ia at $\sim$20 - 35$
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.
We perform multi-dimensional, time-dependent radiation transfer simulations
for hard X-ray and $\gamma$-ray emissions, following radioactive decays of
$^{56}$Ni and $^{56}$Co, 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 with an exposure 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 the upper limit for the mass of
$^{56}$Ni as $\lsim$1.0 M_{\odot}$ 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 or ASTRO-H, launched in 2012 and to be
so in 2014, will reach to SNe Ia at $\sim$15 Mpc, i.e., one SN in a 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
$\sim$25 Mpc, i.e., a few SNe Ia per year. Proposed next generation
$\gamma$-ray missions, e.g., GRIPS, could reach to SNe Ia at $\sim$20 - 35$
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.
Wednesday, August 8, 2012
Self-shielding of Soft X-rays in SN Ia Progenitors. (arXiv:1208.0858v1 [astro-ph.HE])
Self-shielding of Soft X-rays in SN Ia Progenitors. (arXiv:1208.0858v1 [astro-ph.HE]):
There are insufficient super soft (~ 0.1 keV) X-ray sources in either spiral
or elliptical galaxies to account for the rate of explosion of Type Ia
supernovae in either the single degenerate or the double degenerate scenarios.
We quantify the amount of circumstellar matter that would be required to
suppress the soft X-ray flux by yielding a column density in excess of 10^{23}
cm^{-2}. We summarize evidence that appropriate quantities of matter are extant
in SN Ia and in recurrent novae that may be supernova precursors. The obscuring
matter is likely to have a large, but not complete, covering factor and to be
substantially non-spherically symmetric. Assuming that much of the absorbed
X-ray flux is re-radiated as black-body radiation in the UV, we estimate that
fewer than 100 sources might be detectable in the GALEX all sky survey.
There are insufficient super soft (~ 0.1 keV) X-ray sources in either spiral
or elliptical galaxies to account for the rate of explosion of Type Ia
supernovae in either the single degenerate or the double degenerate scenarios.
We quantify the amount of circumstellar matter that would be required to
suppress the soft X-ray flux by yielding a column density in excess of 10^{23}
cm^{-2}. We summarize evidence that appropriate quantities of matter are extant
in SN Ia and in recurrent novae that may be supernova precursors. The obscuring
matter is likely to have a large, but not complete, covering factor and to be
substantially non-spherically symmetric. Assuming that much of the absorbed
X-ray flux is re-radiated as black-body radiation in the UV, we estimate that
fewer than 100 sources might be detectable in the GALEX all sky survey.
Friday, July 27, 2012
Obscuration of Supersoft X-ray Sources by Circumbinary Material - A Way to Hide Type Ia Supernova Progenitors?. (arXiv:1207.6310v1 [astro-ph.SR])
Obscuration of Supersoft X-ray Sources by Circumbinary Material - A Way to Hide Type Ia Supernova Progenitors?. (arXiv:1207.6310v1 [astro-ph.SR]):
The progenitors of supernovae (SNe) type Ia are usually assumed to be either
a single white dwarf (WD) accreting from a non-degenerate companion (the SD
channel) or the result of two merging WDs (DD channel). However, no consensus
currently exists as to which progenitor scenario is the correct one, or whether
the observed SN Ia rate is produced by a combination of both channels. Unlike a
DD progenitor a SD progenitor is expected to emit supersoft X-rays for a
prolonged period of time (~1 Myr) as a result of the burning of accreted matter
on the surface of the WD. An argument against the SD channel as a significant
producer of SNe type Ia has been the lack of observed supersoft X-ray sources
(SSS) and the lower-than-expected integrated soft X-ray flux from elliptical
galaxies.
We wish to determine if it is possible to obscure the supersoft X-ray
emission from a nuclear burning white dwarf in an accreting single degenerate
binary system. In case of obscured systems we wish to determine their general
observational characteristics.
We examine the emergent X-ray emission from a canonical SSS system surrounded
by a spherically symmetric configuration of material, assuming a black body
spectrum with T_BB=50 eV and L=10^38 erg/s. The circumbinary material is
assumed to be of solar chemical abundances, and we leave the mechanism behind
the mass loss into the circumbinary region unspecified.
If steadily accreting, nuclear burning WDs are canonical SSS our analysis
suggests that they can be obscured by relatively modest circumbinary mass loss
rates. This may explain the discrepancy of SSS compared to the SN Ia rate
inferred from observations if the SD progenitor scenario contributes
significantly to the SN Ia rate. Recycled emissions from obscured systems may
be visible in other wavebands than X-rays. It may also explain the lack of
observed SSS in symbiotic binary systems.
The progenitors of supernovae (SNe) type Ia are usually assumed to be either
a single white dwarf (WD) accreting from a non-degenerate companion (the SD
channel) or the result of two merging WDs (DD channel). However, no consensus
currently exists as to which progenitor scenario is the correct one, or whether
the observed SN Ia rate is produced by a combination of both channels. Unlike a
DD progenitor a SD progenitor is expected to emit supersoft X-rays for a
prolonged period of time (~1 Myr) as a result of the burning of accreted matter
on the surface of the WD. An argument against the SD channel as a significant
producer of SNe type Ia has been the lack of observed supersoft X-ray sources
(SSS) and the lower-than-expected integrated soft X-ray flux from elliptical
galaxies.
We wish to determine if it is possible to obscure the supersoft X-ray
emission from a nuclear burning white dwarf in an accreting single degenerate
binary system. In case of obscured systems we wish to determine their general
observational characteristics.
We examine the emergent X-ray emission from a canonical SSS system surrounded
by a spherically symmetric configuration of material, assuming a black body
spectrum with T_BB=50 eV and L=10^38 erg/s. The circumbinary material is
assumed to be of solar chemical abundances, and we leave the mechanism behind
the mass loss into the circumbinary region unspecified.
If steadily accreting, nuclear burning WDs are canonical SSS our analysis
suggests that they can be obscured by relatively modest circumbinary mass loss
rates. This may explain the discrepancy of SSS compared to the SN Ia rate
inferred from observations if the SD progenitor scenario contributes
significantly to the SN Ia rate. Recycled emissions from obscured systems may
be visible in other wavebands than X-rays. It may also explain the lack of
observed SSS in symbiotic binary systems.
Tuesday, July 24, 2012
Some constraints on the lower mass limit for double-degenerate progenitors of Type Ia supernovae. (arXiv:1207.2519v1 [astro-ph.SR])
Some constraints on the lower mass limit for double-degenerate progenitors of Type Ia supernovae. (arXiv:1207.2519v1 [astro-ph.SR]):
Recent theoretical and observational studies both argue that the merging of
double carbon-oxygen white dwarfs (WDs) is responsible for at least some Type
Ia supernovae (SNe Ia). Previous (standard) studies of the anticipated SN
birthrate from this channel have assumed that the merger process is
conservative and that the primary criterion for explosion is that the merged
mass exceeds the Chandrasekhar mass. Han & Webbink (1999) demonstrated that
mass transfer and merger in close double WDs will in many cases be
non-conservative. Pakmor et al. (2011) further suggested that the merger
process should be violent in order to initiate an explosion. We have therefore
investigated how the SN Ia birthrate from the double-degenerate (DD) channel is
affected by these constraints. Using the binary-star population-synthesis
method, we have calculated the DD SN Ia birthrate under conservative and
non-conservative approximations, and including lower mass and mass-ratio limits
indicated by recent smoothed-particle-hydrodynamic calculations. The predicted
DD SN Ia rate is significantly reduced by all of these constraints. With
dynamical mass loss alone (violent merger) the birthrate is reduced to 56% of
the conservative rate. Requiring that the mass ratio $q>2/3$ further reduces
the birthrate to 18% that of the standard assumption. An upper limit of 0.0061
SNuM, or a Galactic rate of $4.6 \times 10^{-4}{\rm yr}^{-1}$, might be
realistic.
Recent theoretical and observational studies both argue that the merging of
double carbon-oxygen white dwarfs (WDs) is responsible for at least some Type
Ia supernovae (SNe Ia). Previous (standard) studies of the anticipated SN
birthrate from this channel have assumed that the merger process is
conservative and that the primary criterion for explosion is that the merged
mass exceeds the Chandrasekhar mass. Han & Webbink (1999) demonstrated that
mass transfer and merger in close double WDs will in many cases be
non-conservative. Pakmor et al. (2011) further suggested that the merger
process should be violent in order to initiate an explosion. We have therefore
investigated how the SN Ia birthrate from the double-degenerate (DD) channel is
affected by these constraints. Using the binary-star population-synthesis
method, we have calculated the DD SN Ia birthrate under conservative and
non-conservative approximations, and including lower mass and mass-ratio limits
indicated by recent smoothed-particle-hydrodynamic calculations. The predicted
DD SN Ia rate is significantly reduced by all of these constraints. With
dynamical mass loss alone (violent merger) the birthrate is reduced to 56% of
the conservative rate. Requiring that the mass ratio $q>2/3$ further reduces
the birthrate to 18% that of the standard assumption. An upper limit of 0.0061
SNuM, or a Galactic rate of $4.6 \times 10^{-4}{\rm yr}^{-1}$, might be
realistic.
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