TYPE Ib SUPERNOVA 2008D ASSOCIATED WITH THE LUMINOUS X-RAY TRANSIENT 080109: AN ENERGETIC EXPLOSION OF A MASSIVE HELIUM STAR (original) (raw)
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The Astrophysical Journal, 2015
We present the SuperNova Explosion Code (SNEC), an open-source Lagrangian code for the hydrodynamics and equilibrium-diffusion radiation transport in the expanding envelopes of supernovae. Given a model of a progenitor star, an explosion energy, and an amount and distribution of radioactive nickel, SNEC generates the bolometric light curve, as well as the light curves in different broad bands assuming black body emission. As a first application of SNEC, we consider the explosions of a grid of 15 M (at zero-age main sequence) stars whose hydrogen envelopes are stripped to different extents and at different points in their evolution. The resulting light curves exhibit plateaus with durations of ∼20 − 100 days if 1.5 − 2 M of hydrogen-rich material is left and no plateau if less hydrogen-rich material is left. If these shorter plateau lengths are not seen for Type IIP supernovae in nature, it suggests that, at least for zero-age main sequence masses 20 M , hydrogen mass loss occurs as an all or nothing process. This perhaps points to the important role binary interactions play in generating the observed mass-stripped supernovae (i.e., Type Ib/c events). These light curves are also unlike what is typically seen for Type IIL supernovae, arguing that simply varying the amount of mass loss cannot explain these events. The most stripped models begin to show double-peaked light curves similar to what is often seen for Type IIb supernovae, confirming previous work that these supernovae can come from progenitors that have a small amount of hydrogen and a radius of ∼ 500 R .
The response of a helium white dwarf to an exploding Type Ia supernova
Monthly Notices of the Royal Astronomical Society, 2015
We conduct numerical simulations of the interacting ejecta from an exploding CO white dwarf (WD) with the He WD donor in the double-detonation scenario for Type Ia supernovae (SNe Ia), and find that the descendant supernova remnant (SNR) is highly asymmetrical, in contradiction with observations. When the donor He WD has low mass, M WD = 0.2M ⊙ , it is at a distance of ∼ 0.08R ⊙ from the explosion, and helium is not ignited. The low mass He WD casts an 'ejecta shadow' behind it, that has imprint in the SN remnant (SNR) hundreds of years later. The outer parts of the shadowed side are fainter and its boundary with the ambient gas is somewhat flat. These features are not found in known SNRs. More massive He WD donors, M WD ≃ 0.4M ⊙ , must be closer to the CO WD to transfer mass. At a distance a 0.045R ⊙ helium is ignited and the He WD explodes. This explosion leads to a highly asymmetrical SNR and to ejection of ∼ 0.15M ⊙ of helium, both of which contradict observations of SNe Ia.
The metamorphosis of supernova SN 2008D/XRF 080109: a link between supernovae and GRBs/hypernovae
Science (New York, N.Y.), 2008
The only supernovae (SNe) to show gamma-ray bursts (GRBs) or early x-ray emission thus far are overenergetic, broad-lined type Ic SNe (hypernovae, HNe). Recently, SN 2008D has shown several unusual features: (i) weak x-ray flash (XRF), (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SN Ic HNe, and (iv) development of helium lines as in SNe Ib. Detailed analysis shows that SN 2008D was not a normal supernova: Its explosion energy (E approximately 6x10(51) erg) and ejected mass [ approximately 7 times the mass of the Sun (M(middle dot in circle))] are intermediate between normal SNe Ibc and HNe. We conclude that SN 2008D was originally a approximately 30 M(middle dot in circle) star. When it collapsed, a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse...
The Explosion Mechanism of Core-Collapse Supernovae: Progress in Supernova Theory and Experiments
Publications of the Astronomical Society of Australia, 2015
The explosion of core-collapse supernova depends on a sequence of events taking place in less than a second in a region of a few hundred kilometers at the center of a supergiant star, after the stellar core approaches the Chandrasekhar mass and collapses into a proto-neutron star, and before a shock wave is launched across the stellar envelope. Theoretical efforts to understand stellar death focus on the mechanism which transforms the collapse into an explosion. Progress in understanding this mechanism is reviewed with particular attention to its asymmetric character. We highlight a series of successful studies connecting observations of supernova remnants and pulsars properties to the theory of core-collapse using numerical simulations. The encouraging results from first principles models in axisymmetric simulations is tempered by new puzzles in 3D. The diversity of explosion paths and the dependence on the pre-collapse stellar structure is stressed, as well as the need to gain a better understanding of hydrodynamical and MHD instabilities such as SASI and neutrino-driven convection. The shallow water analogy of shock dynamics is presented as a comparative system where buoyancy effects are absent. This dynamical system can be studied numerically and also experimentally with a water fountain. The potential of this complementary research tool for supernova theory is analyzed. We also review its potential for public outreach in science museums.
The Unique Type Ib Supernova 2005bf: A WN Star Explosion Model for Peculiar Light Curves and Spectra
The Astrophysical Journal, 2005
Observations and modeling for the light curve (LC) and spectra of supernova (SN) 2005bf are reported. This SN showed unique features: the LC had two maxima, and declined rapidly after the second maximum, while the spectra showed strengthening He lines whose velocity increased with time. The double-peaked LC can be reproduced by a double-peaked 56 Ni distribution, with most 56 Ni at low velocity and a small amount at high velocity. The rapid post-maximum decline requires a large fraction of the γ-rays to escape from the 56 Ni-dominated region, possibly because of low-density "holes". The presence of Balmer lines in the spectrum suggests that the He layer of the progenitor was substantially intact. Increasing γ-ray deposition in the He layer due to enhanced γ-ray escape from the 56 Ni-dominated region may explain both the delayed strengthening and the increasing velocity of the He lines. The SN has massive ejecta (∼ 6−7M ⊙), normal kinetic energy (∼ 1.0 − 1.5 × 10 51 ergs), high peak bolometric luminosity (∼ 5 × 10 42 erg s −1) for an epoch as late as ∼ 40 days, and a large 56 Ni mass (∼ 0.32M ⊙). These properties, and the presence of a small amount of H suggest that the progenitor was initially massive (M∼ 25 − 30M ⊙) and had lost most of its H envelope, and was possibly a WN star. The double-peaked 56 Ni distribution suggests that the explosion may have formed jets that did not reach the He layer. The properties of SN 2005bf resemble those of the explosion of Cassiopeia A.
Single point off-center helium ignitions as origin of some Type Ia supernovae
International Symposium on …, 2006
The explosion of a helium layer accreted on top of a white dwarf, leading to the subsequent explosion of the star (while the accreting dwarf is still below the Chandrasekhar mass limit) is an alternative model for some subluminous Type Ia supernovae explosions. In this communication we present two preliminary hydrodynamical simulations concerning these socalled Sub-Chandrasekhar mass models for Type Ia supernovae, calculated in two dimensions. In the first calculation we have assumed one single detonation travelling through the helium layer which, after a while, induces the detonation of the carbon layer at the antipodes of the original ignition point. In the second case we assumed the prompt detonation of the carbon just beneath the ignition point. A comparison between these two models is presented.