Preprint typeset using LATEX style emulateapj v. 11/10/09 RAPIDLY DECAYING SUPERNOVA 2010X: A CANDIDATE “.IA ” EXPLOSION (original) (raw)
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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 Astrophysical Journal, 2009
We present a theoretical model for supernova (SN) 2008D associated with the luminous X-ray transient 080109. The bolometric light curve and optical spectra of the SN are modelled based on the progenitor models and the explosion models obtained from hydrodynamic/nucleosynthetic calculations. We find that SN 2008D is a more energetic explosion than normal core-collapse supernovae, with an ejecta mass of M ej = 5.3 ± 1.0 M ⊙ and a kinetic energy of E K = 6.0 ± 2.5 × 10 51 erg. The progenitor star of the SN has a 6 − 8M ⊙ He core with essentially no H envelope (< 5 × 10 −4 M ⊙) prior to the explosion. The main-sequence mass of the progenitor is estimated to be M MS = 20 − 25 M ⊙ , with additional systematic uncertainties due to convection, mass loss, rotation, and binary effects. These properties are intermediate between those of normal SNe and hypernovae associated with gamma-ray bursts. The mass of the central remnant is estimated as 1.6 − 1.8M ⊙ , which is near the boundary between neutron star and black hole formation.
Monthly Notices of the Royal Astronomical Society, 2016
Spectrophotometry of SN 1996al carried out throughout 15 yr is presented. The early photometry suggests that SN 1996al is a linear Type II supernova, with an absolute peak of M V ∼ −18.2 mag. Early spectra present broad asymmetric Balmer emissions, with superimposed narrow lines with P-Cygni profile, and He I features with asymmetric broad emission components. The analysis of the line profiles shows that the H and He broad components form in the same region of the ejecta. By day +142, the Hα profile dramatically changes: the narrow P-Cygni profile disappears, and the Hα is fitted by three emission components that will be detected over the remaining 15 yr of the supernova (SN) monitoring campaign. Instead, the He I emissions become progressively narrower and symmetric. A sudden increase in flux of all He I lines is observed between 300 and 600 d. Models show that the SN luminosity is sustained by the interaction of low-mass (∼1.15 M) ejecta, expelled in a low kinetic energy (∼1.6 × 10 50 erg) explosion, with highly asymmetric circumstellar medium. The detection of Hα emission in pre-explosion archive images suggests that the progenitor was most likely a massive star (∼25 M ZAMS) that had lost a large fraction of its hydrogen envelope before explosion, and was hence embedded in a H-rich cocoon. The low-mass ejecta and modest kinetic energy of the explosion are explained with massive fallback of material into the compact remnant, a 7-8-M black hole.
A hybrid type Ia supernova with an early flash triggered by helium-shell detonation
Nature, 2017
Type Ia supernovae arise from the thermonuclear explosion of white-dwarf stars that have cores of carbon and oxygen. The uniformity of their light curves makes these supernovae powerful cosmological distance indicators, but there have long been debates about exactly how their explosion is triggered and what kind of companion stars are involved. For example, the recent detection of the early ultraviolet pulse of a peculiar, subluminous type Ia supernova has been claimed as evidence for an interaction between a red-giant or a main-sequence companion and ejecta from a white-dwarf explosion. Here we report observations of a prominent but red optical flash that appears about half a day after the explosion of a type Ia supernova. This supernova shows hybrid features of different supernova subclasses, namely a light curve that is typical of normal-brightness supernovae, but with strong titanium absorption, which is commonly seen in the spectra of subluminous ones. We argue that this early ...
Supernovae from Direct Collisions of White Dwarfs and the Role of Helium Shell Ignition
The Astrophysical Journal, 2016
Models for supernovae (SNe) arising from thermonuclear explosions of white dwarfs (WDs) have been extensively studied over the last few decades, mostly focusing on the single degenerate (accretion of material of a WD) and double degenerate (WD-WD merger) scenarios. In recent years it was suggested that WD-WD direct collisions provide an additional channel for such explosions. Here we extend the studies of such explosions, and explore the role of Helium-shells in affecting the thermonuclear explosions. We study both the impact of low-mass helium (∼ 0.01 M ⊙) shells, as well as high mass shells (≥ 0.1 M ⊙). We find that detonation of the massive helium layers precede the detonation of the WD Carbon-Oxygen (CO) bulk during the collision and can change the explosive evolution and outcomes for the cases of high mass He-shells. In particular, the He-shell detonation propagates on the WD surface and inefficiently burns material prior to the CO detonation that later follows in the central parts of the WD. Such evolution leads to larger production of intermediate elements, producing larger yields of 44 Ti and 48 Cr relative to the pure CO-CO WD collisions. Collisions of WDs with a low-mass He-shell do not give rise to helium detonation, but helium burning does precede the CO bulk detonation. Such collisions produce a high velocity, low-mass of ejected burned material enriched with intermediate elements, with smaller changes to the overall explosion outcomes. The various effects arising from the contribution of low/high mass He layers change the kinematics and the morphological structure of collision-induced SNe and may thereby provide unique observational signatures for such SNe, and play a role in the chemical enrichment of galaxies and the production of intermediate elements and positrons from their longer-term decay.