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ABSTRACT: The discovery of supernovae associated with long-duration gamma ray burst
observations is primary evidence that the progenitors of these outbursts are
massive stars. One of the principle mysteries in understanding these
progenitors has been the fact that all of these gamma-ray burst associated
supernovae are type Ic supernovae, with no evidence of helium in the stellar
atmosphere. Many studies have focused on whether or not this helium is simply
hidden from spectral analyses. In this paper, we show results from recent
stellar models using new convection algorithms based on our current
understanding of stellar mixing. We demonstrate that enhanced convection may
lead to severe depletion of stellar helium layers, suggesting that the helium
is not observed simply because it is not in the star. We also present
light-curves and spectra of these compact helium-depleted stars, compared to
models with more conventional helium layers.
05/2013;
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ABSTRACT: Supermassive primordial stars are expected to form in a small fraction of
massive protogalaxies in the early universe, and are generally conceived of as
the progenitors of the seeds of supermassive black holes (BHs) at high
redshift. Supermassive stars with masses of ~ 55,000 M_Sun, however, have been
found to explode and completely disrupt in a supernova (SN) with an energy of
up to ~ 10^55 erg, instead of collapsing to a BH. Such events, roughly 10,000
times more energetic than typical SNe today, would be among the biggest
explosions in the history of the universe. We carry out a simulation of such a
supermassive star SN in two stages. Using the RAGE radiation hydrodynamics code
we first evolve the explosion from the earliest stages, through the breakout of
the shock from the surface of the star until the blast wave has propagated out
to several parsecs from the explosion site, which lies deep within an atomic
cooling dark matter (DM) halo at z ~ 15. Then, using the GADGET cosmological
hydrodynamics code we evolve the explosion out to several kiloparsecs from the
explosion site, far into the low-density intergalactic medium. The host DM
halo, with a total mass of 4 x 10^7 M_Sun, much more massive than typical
primordial star-forming halos, is completely evacuated of high density gas
after < 10 Myr, although dense metal-enriched gas recollapses into the halo,
where it will likely form second-generation stars after > 70 Myr. The ~ 20,000
M_Sun in metals that are released in the explosion are widely distributed, and
enrich the dense recollapsing gas to an average metallicity of ~ 0.05 Z_Sun.
Such a high level of enrichment suggests that the chemical signature of these
supermassive star explosions may have been missed in previous surveys of
metal-poor stars.
04/2013;
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[show abstract]
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ABSTRACT: The detection of Pop III supernovae could directly probe the primordial IMF
for the first time, unveiling the properties of the first galaxies, early
chemical enrichment and reionization, and the seeds of supermassive black
holes. Growing evidence that some Pop III stars were less massive than 100
solar masses may complicate prospects for their detection, because even though
they would have been more plentiful they would have died as core-collapse
supernovae, with far less luminosity than pair-instability explosions. This
picture greatly improves if the SN shock collides with a dense circumstellar
shell ejected during a prior violent LBV type eruption. Such collisions can
turn even dim SNe into extremely bright ones whose luminosities can rival those
of pair-instability SNe. We present simulations of Pop III Type IIn SN light
curves and spectra performed with the Los Alamos RAGE and SPECTRUM codes.
Taking into account Lyman-alpha absorption in the early universe and
cosmological redshifting, we find that 40 solar mass Pop III Type IIn SNe will
be visible out to z ~ 20 with JWST and out to z ~ 7 with WFIRST. Thus, even low
mass Pop III SNe can be used to probe the primeval universe.
02/2013;
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Fiona A. Harrison,
William W. Craig,
Finn E. Christensen,
Charles J. Hailey,
Will W. Zhang,
Steven E. Boggs,
Daniel Stern,
W. Rick Cook,
Karl Forster,
Paolo Giommi, [......],
Lorenzo Natalucci,
Patrick Ogle,
Eran O. Ofek,
Andrew Ptak,
Stephen P. Reynolds,
Jand R. Rigby,
Gianpiero Tagliaferri,
Stephen E. Thorsett,
Ezequiel Treister,
C. Megan Urry
[show abstract]
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ABSTRACT: The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 13
June 2012, is the first focusing high-energy X-ray telescope in orbit. NuSTAR
operates in the band from 3 -- 79 keV, extending the sensitivity of focusing
far beyond the ~10 keV high-energy cutoff achieved by all previous X-ray
satellites. The inherently low-background associated with concentrating the
X-ray light enables NuSTAR to probe the hard X-ray sky with a more than
one-hundred-fold improvement in sensitivity over the collimated or coded-mask
instruments that have operated in this bandpass. Using its unprecedented
combination of sensitivity, spatial and spectral resolution, NuSTAR will pursue
five primary scientific objectives, and will also undertake a broad program of
targeted observations. The observatory consists of two co-aligned
grazing-incidence X-ray telescopes pointed at celestial targets by a three-axis
stabilized spacecraft. Deployed into a 600 km, near-circular, 6degree
inclination orbit, the Observatory has now completed commissioning, and is
performing consistent with pre-launch expectations. NuSTAR is now executing its
primary science mission, and with an expected orbit lifetime of ten years, we
anticipate proposing a guest investigator program, to begin in Fall 2014.
01/2013;
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ABSTRACT: Gravitational-wave observations of compact binaries have the potential to
uncover the distribution of masses and angular momenta of black holes and
neutron stars in the universe. The binary components' physical parameters can
be inferred from their effect on the phasing of the gravitational-wave signal,
but a partial degeneracy between the components' mass ratio and their angular
momenta limits our ability to measure the individual component masses. At the
typical signal amplitudes expected by the Advanced Laser Interferometer
Gravitational-wave Observatory (signal-to-noise ratios between 10 and 20), we
show that it will in many cases be difficult to distinguish whether the
components are neutron stars or black holes. We identify when the masses of the
binary components could be unambiguously measured outside the range of current
observations: a system with a chirp mass $\mathcal{M} \le 0.871 $ M$_\odot$
would unambiguously contain the smallest-mass neutron star observed, and a
system with $\mathcal{M} \ge 2.786 \Msun$ must contain a black hole. However,
additional information would be needed to distinguish between a binary
containing two 1.35 M$_\odot$ neutron stars and an exotic
neutron-star--black-hole binary. We also identify those configurations that
could be unambiguously identified as black-hole binaries, and show how the
observation of an electromagnetic counterpart to a neutron-star--black-hole
binary could be used to constrain the black-hole spin.
01/2013;
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Daniel J. Whalen,
Wesley Even,
Lucille H. Frey,
Jarrett L. Johnson,
C. C. Lovekin, Chris L. Fryer,
Massimo Stiavelli,
Daniel E. Holz,
Alexander Heger,
S. E. Woosley,
Aimee L. Hungerford
[show abstract]
[hide abstract]
ABSTRACT: The first stars are the key to the formation of primitive galaxies, early
cosmological reionization and chemical enrichment, and the origin of
supermassive black holes. Unfortunately, in spite of their extreme
luminosities, individual Population III stars will likely remain beyond the
reach of direct observation for decades to come. However, their properties
could be revealed by their supernova explosions, which may soon be detected by
a new generation of NIR observatories such as JWST and WFIRST. We present light
curves and spectra for Pop III pair-instability supernovae calculated with the
Los Alamos radiation hydrodynamics code RAGE. Our numerical simulations account
for the interaction of the blast with realistic circumstellar envelopes, the
opacity of the envelope, and Lyman absorption by the neutral IGM at high
redshift, all of which are crucial to computing the NIR signatures of the first
cosmic explosions. We find that JWST will detect pair-instability supernovae
out to z > 30, WFIRST will detect them in all-sky surveys out to z ~ 15 - 20
and LSST and Pan-STARRS will find them at z ~ 7 - 8. The discovery of these
ancient explosions will probe the first stellar populations and reveal the
existence of primitive galaxies that might not otherwise have been detected.
11/2012;
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ABSTRACT: The existence of supermassive black holes as early as z ~ 7 is one of the
great unsolved problems in cosmological structure formation. One leading theory
argues that they are born during catastrophic baryon collapse in z ~ 15
protogalaxies in strong Lyman-Werner UV backgrounds. Atomic line cooling in
such galaxies fragments baryons into massive clumps that are thought to
directly collapse to 10^4 - 10^5 solar-mass black holes. We have now discovered
that some of these fragments can instead become supermassive stars that
eventually explode as pair-instability supernovae with energies of ~ 10^55 erg,
the most energetic explosions in the universe. We have calculated light curves
and spectra for supermassive Pop III PI SNe with the Los Alamos RAGE and
SPECTRUM codes. We find that they will be visible in NIR all-sky surveys by
WFIRST and WISH out to z ~ 20, perhaps revealing the birthplaces of the first
quasars.
11/2012;
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Amanda J. Bayless,
Tyler Pritchard,
Peter W. A. Roming,
Paul Kuin,
Peter J. Brown,
Maria Teresa Botticella,
Massimo Dall'Ora,
Lucille H. Frey,
Wesley Even, Chris L. Fryer,
Justyn R. Maund,
Morgan Fraser
[show abstract]
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ABSTRACT: Observations with the Swift UVOT have unambiguously uncovered for the first
time a long-lived, UV "plateau" in a Type II-P supernova (SN).
Although this flattening in slope is hinted at in a few other SNe, due to its
proximity and minimal line-of-sight extinction, SN 2012aw has afforded the
first opportunity to clearly observe this UV plateau. The observations of SN
2012aw revealed all Swift UV and u-band lightcurves initially declined rapidly,
but 27 days after explosion the light curves flattened. Some possible sources
of the UV plateau are: the same thermal process that cause the optical plateau,
heating from radioactive decay, or a combination of both processes.
10/2012;
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ABSTRACT: The first stars ended the cosmic Dark Ages and created the first heavy
elements necessary for the formation of planets and life. The properties of
these stars remain uncertain, and it may be decades before individual Pop III
stars are directly observed. Their masses, however, can be inferred from their
supernova explosions, which may soon be found in both deep-field surveys by
JWST and in all-sky surveys by WFIRST. We have performed radiation
hydrodynamical simulations of the near infrared signals of Pop III
pair-instability supernovae in realistic circumstellar environments with Lyman
absorption by the neutral intergalactic medium. We find that JWST and WFIRST
will detect these explosions out to z ~ 30 and 20, respectively, unveiling the
first generation of stars in the universe.
09/2012;
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[show abstract]
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ABSTRACT: BH-NS and BH-BH systems are among the most promising gravitational wave
sources detectable by advanced LIGO/VIRGO and the Einstein Telescope. Although
the rates of these systems may be above those of NS-NS mergers, BH-NS and BH-BH
systems are difficult to detect, and thusfar none have been observed. But the
progenitors of BH-NS and BH-BH binary systems may have been observed, in the
form of High-Mass X-ray Binaries (HMXBs). In this paper, we continue work
studying these potential progenitors of these important gravitational wave
sources. In the first two papers of the series, we have demonstrated that IC10
X-1 and NGC300 X-1 are direct progenitors of BH-BH systems and that Cyg X-1 may
form, alas with a very low probability, a BH-NS system. Here, we analyze the
Galactic binaries GX 301-2, Vela X-1, XTEJ1855-026, 4U1907+09, Cir X-1 and
extra-galactic LMC X-1, LMC X-3, M33 X-1. In each case, we find that the future
evolution will not allow the formation of a BH-NS nor a BH-BH system. Most of
these binaries will soon merge in the common envelope phase, with a compact
object sinking into a helium-rich core of a stellar companion. This
"helium-merger" may be a progenitor for long duration gamma-ray bursts (GRBs).
Based on the observed HMXB population, the rate of helium-mergers may make up a
sizable fraction of long-duration GRBs. Due to this high number of potential
GRB progenitors, a chance that a Galactic HMXB has caused one of the recent
major mass extinction events is significant (10-20%).
08/2012;
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[show abstract]
[hide abstract]
ABSTRACT: A leading formation scenario for R Coronae Borealis (RCB) stars invokes the
merger of degenerate He and CO white dwarfs (WD) in a binary. The observed
ratio of 16O/18O for RCB stars is in the range of 0.3-20 much smaller than the
solar value of ~500. In this paper, we investigate whether such a low ratio can
be obtained in simulations of the merger of a CO and a He white dwarf. We
present the results of five 3-dimensional hydrodynamic simulations of the
merger of a double white dwarf system where the total mass is 0.9 Mdot and the
initial mass ratio (q) varies between 0.5 and 0.99. We identify in simulations
with $q\lesssim0.7$ a feature around the merged stars where the temperatures
and densities are suitable for forming 18O. However, more 16O is being
dredged-up from the C- and O-rich accretor during the merger than the amount of
18O that is produced. Therefore, on a dynamical time scale over which our
hydrodynamics simulation runs, a 16O/18O ratio of ~2000 in the "best" case is
found. If the conditions found in the hydrodynamic simulations persist for 10^6
seconds the oxygen ratio drops to 16 in one case studied, while in a hundred
years it drops to ~4 in another case studied, consistent with the observed
values in RCB stars. Therefore, the merger of two white dwarfs remains a strong
candidate for the formation of these enigmatic stars.
08/2012;
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[show abstract]
[hide abstract]
ABSTRACT: It is now generally accepted that long-duration gamma ray bursts (GRBs) are
due to the collapse of massive rotating stars. The precise collapse process
itself, however, is not yet fully understood. Strong winds, outbursts, and
intense ionizing UV radiation from single stars or strongly interacting
binaries are expected to destroy the molecular cloud cores that give birth to
them and create highly complex circumburst environments for the explosion. Such
environments might imprint features on GRB light curves that uniquely identify
the nature of the progenitor and its collapse. We have performed numerical
simulations of realistic environments for a variety of long-duration GRB
progenitors with ZEUS-MP, and have developed an analytical method for
calculating GRB light curves in these profiles. Though a full,
three-dimensional, relativistic magnetohydrodynamical computational model is
required to precisely describe the light curve from a GRB in complex
environments, our method can provide a qualitative understanding of these
phenomena. We find that, in the context of the standard afterglow model,
massive shells around GRBs produce strong signatures in their light curves, and
that this can distinguish them from those occurring in uniform media or steady
winds. These features can constrain the mass of the shell and the properties of
the wind before and after the ejection. Moreover, the interaction of the GRB
with the circumburst shell is seen to produce features that are consistent with
observed X-ray flares that are often attributed to delayed energy injection by
the central engine. Our algorithm for computing light curves is also applicable
to GRBs in a variety of environments such as those in high-redshift
cosmological halos or protogalaxies, both of which will soon be targets of
future surveys such as JANUS or Lobster.
04/2012;
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[show abstract]
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ABSTRACT: We have entered the era of explosive transient astronomy, in which upcoming
real-time surveys like the Large Synoptic Survey Telescope (LSST), the Palomar
Transient Factory (PTF) and Panoramic Survey Telescope and Rapid Response
System (Pan-STARRS) will detect supernovae in unprecedented numbers. Future
telescopes such as the James Webb Space Telescope may discover supernovae from
the earliest stars in the universe and reveal their masses. The observational
signatures of these astrophysical transients are the key to unveiling their
central engines, the environments in which they occur, and to what precision
they will pinpoint cosmic acceleration and the nature of dark energy. We
present a new method for modeling supernova light curves and spectra with the
radiation hydrodynamics code RAGE coupled with detailed monochromatic opacities
in the SPECTRUM code. We include a suite of tests that demonstrate how the
improved physics is indispensable to modeling shock breakout and light curves.
03/2012;
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[show abstract]
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ABSTRACT: We use three-dimensional hydrodynamical simulations to study the rapid infall phase of the common envelope (CE) interaction of a red giant branch star of mass equal to 0.88 M ☉ and a companion star of mass ranging from 0.9 down to 0.1 M ☉. We first compare the results obtained using two different numerical techniques with different resolutions, and find very good agreement overall. We then compare the outcomes of those simulations with observed systems thought to have gone through a CE. The simulations fail to reproduce those systems in the sense that most of the envelope of the donor remains bound at the end of the simulations and the final orbital separations between the donor's remnant and the companion, ranging from 26.8 down to 5.9 R ☉, are larger than the ones observed. We suggest that this discrepancy vouches for recombination playing an essential role in the ejection of the envelope and/or significant shrinkage of the orbit happening in the subsequent phase.
The Astrophysical Journal 12/2011; 744(1):52. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We use three-dimensional hydrodynamical simulations to study the rapid infall
phase of the common envelope interaction of a red giant branch star of mass
equal to 0.88 \msun and a companion star of mass ranging from 0.9 down to 0.1
\msun. We first compare the results obtained using two different numerical
techniques with different resolutions, and find overall very good agreement. We
then compare the outcomes of those simulations with observed systems thought to
have gone through a common envelope. The simulations fail to reproduce those
systems in the sense that most of the envelope of the donor remains bound at
the end of the simulations and the final orbital separations between the
donor's remnant and the companion, ranging from 26.8 down to 5.9 \rsun, are
larger than the ones observed. We suggest that this discrepancy vouches for
recombination playing an essential role in the ejection of the envelope and/or
significant shrinkage of the orbit happening in the subsequent phase.
07/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We present three-dimensional hydrodynamical simulations of the fast in-spiral phase of the common envelope interaction between a red giant star and a range of companions with different masses. In order to verify the reliability of the numerics we use two different approaches. The code-to-code comparison shows consistent results. We then compare the outcomes of our simulations to post common envelope systems. At the end of the simulations, most of the envelope of the progenitor is still bound to the system and the orbital separations are systematically larger than those observed. We explain what the reasons for this discrepancy might be and how we will proceed with our investigation.
Evolution of Compact Binaries, Vina del Mar, Chile; 01/2011
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Chris L. Fryer,
Ashley J. Ruiter,
Krzysztof Belczynski,
Peter J. Brown,
Filomena Bufano,
Steven Diehl,
Christopher J. Fontes,
Lucille H. Frey,
Stephen T. Holland,
Aimee L. Hungerford,
Stefan Immler,
Paolo Mazzali,
Casey Meakin,
Peter A. Milne,
Cody Raskin,
and Francis X. Timmes
[show abstract]
[hide abstract]
ABSTRACT: The merger of two white dwarfs (aka double-degenerate merger) has often been cited as a potential progenitor of Type Ia supernovae. Here we combine population synthesis, merger, and explosion models with radiation-hydrodynamics light-curve models to study the implications of such a progenitor scenario on the observed Type Ia supernova population. Our standard model, assuming double-degenerate mergers do produce thermonuclear explosions, produces supernova light curves that are broader than the observed type Ia sample. In addition, we discuss how the shock breakout and spectral features of these double-degenerate progenitors will differ from the canonical bare Chandrasekhar-massed explosion models. We conclude with a discussion of how one might reconcile these differences with current observations.
The Astrophysical Journal 11/2010; 725(1):296. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Depending on mass and metallicity as well as evolutionary phase, stars
occasionally experience convective-reactive nucleosynthesis episodes. We
specifically investigate the situation when nucleosynthetically unprocessed,
H-rich material is convectively mixed with a He-burning zone, for example in
convectively unstable shell on top of electron-degenerate cores in AGB stars,
young white dwarfs or X-ray bursting neutron stars. Such episodes are
frequently encountered in stellar evolution models of stars of extremely low or
zero metal content [...] We focus on the convective-reactive episode in the
very-late thermal pulse star Sakurai's object (V4334 Sagittarii). Asplund etal.
(1999) determined the abundances of 28 elements, many of which are highly
non-solar, ranging from H, He and Li all the way to Ba and La, plus the C
isotopic ratio. Our simulations show that the mixing evolution according to
standard, one-dimensional stellar evolution models implies neutron densities in
the He that are too low to obtain a significant neutron capture nucleosynthesis
on the heavy elements. We have carried out 3D hydrodynamic He-shell flash
convection [...] we assume that the ingestion process of H into the He-shell
convection zone leads only after some delay time to a sufficient entropy
barrier that splits the convection zone [...] we obtain significantly higher
neutron densities (~few 10^15 1/cm^3) and reproduce the key observed abundance
trends found in Sakurai's object. These include an overproduction of Rb, Sr and
Y by about 2 orders of magnitude higher than the overproduction of Ba and La.
Such a peculiar nucleosynthesis signature is impossible to obtain with the
mixing predictions in our one-dimensional stellar evolution models. [...] We
determine how our results depend on uncertainties of nuclear reaction rates,
for example for the C13(\alpha, n)O16 reaction.
02/2010;
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[show abstract]
[hide abstract]
ABSTRACT: GRB 080913 and GRB 090423 are the most distant gamma-ray bursts (GRBs) known to date, with spectroscopically determined redshifts of z = 6.7 and z = 8.1, respectively. The detection of bursts at this early epoch of the universe significantly constrains the nature of GRBs and their progenitors. We perform population synthesis studies of the formation and evolution of early stars, and calculate the resulting formation rates of short- and long-duration GRBs at high redshift. The peak of the GRB rate from Population II stars occurs at z ~ 7 for a model with efficient/fast mixing of metals, while it is found at z ~ 3 for an inefficient/slow metallicity evolution model. We show that in the redshift range 6 z 10, essentially all GRBs originate from Population II stars, regardless of the metallicity evolution model. These stars (having small, but non-zero metallicity) are the most likely progenitors for both long GRBs (collapsars) and short GRBs (neutron star-neutron star or blackhole-neutron star mergers) at this epoch. Although the predicted intrinsic rates of long and short GRBs are similar at these high redshifts, observational selection effects lead to higher (a factor of ~10) observed rates for long GRBs. We conclude that the two recently observed high-z GRB events are most likely long GRBs originating from Population II collapsars.
The Astrophysical Journal 12/2009; 708(1):117. · 6.02 Impact Factor
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Chris L. Fryer,
Peter J. Brown,
Filomena Bufano,
Jon A. Dahl,
Christopher J. Fontes,
Lucille H. Frey,
Stephen T. Holland,
Aimee L. Hungerford,
Stefan Immler,
Paolo Mazzali,
Peter A. Milne,
Evan Scannapieco,
Nevin Weinberg,
Patrick A. Young
[show abstract]
[hide abstract]
ABSTRACT: Astronomers have proposed a number of mechanisms to produce supernova explosions. Although many of these mechanisms are now not considered primary engines behind supernovae, they do produce transients that will be observed by upcoming ground-based surveys and NASA satellites. Here we present the first radiation-hydrodynamics calculations of the spectra and light curves from three of these "failed" supernovae: supernovae with considerable fallback, accretion induced collapse of white dwarfs, and energetic helium flashes (also known as type .Ia supernovae). Comment: 33 pages, 14 figures
The Astrophysical Journal 08/2009; · 6.02 Impact Factor
