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تسجيل مستخدم جديدA hybrid type Ia supernova with an early flash triggered by helium-shell detonation
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Type Ia supernovae (SNe Ia) arise from the thermonuclear explosion of carbon-oxygen white dwarfs. Though the uniformity of their light curves makes them powerful cosmological distance indicators, long-standing issues remain regarding their progenitors and explosion mechanisms. Recent detection of the early ultraviolet pulse of a peculiar subluminous SN Ia has been claimed as new evidence for the companion-ejecta interaction through the single-degenerate channel. Here, we report the discovery of a prominent but red optical flash at $sim$ 0.5 days after the explosion of a SN Ia which shows hybrid features of different SN Ia sub-classes: a light curve typical of normal-brightness SNe Ia, but with strong titanium absorptions, commonly seen in the spectra of subluminous ones. We argue that the early flash of such a hybrid SN Ia is different from predictions of previously suggested scenarios such as the companion-ejecta interaction. Instead it can be naturally explained by a SN explosion triggered by a detonation of a thin helium shell either on a near-Chandrasekhar-mass white dwarf ($gtrsim$ 1.3 M$_{odot}$) with low-yield $^{56}$Ni or on a sub-Chandrasekhar-mass white dwarf ($sim$ 1.0 M$_{odot}$) merging with a less massive white dwarf. This finding provides compelling evidence that one branch of the previously proposed explosion models, the helium-ignition scenario, does exist in nature, and such a scenario may account for explosions of white dwarfs in a wider mass range in contrast to what was previously supposed.
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The double-detonation explosion model has been considered a candidate for explaining astrophysical transients with a wide range of luminosities. In this model, a carbon-oxygen white dwarf star explodes following detonation of a surface layer of heliu
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We present observational data for a peculiar supernova discovered by the OGLE-IV survey and followed by the Public ESO Spectroscopic Survey for Transient Objects. The inferred redshift of $z=0.07$ implies an absolute magnitude in the rest-frame $I$-b
and of M$_{I}sim-17.6$ mag. This places it in the luminosity range between normal Type Ia SNe and novae. Optical and near infrared spectroscopy reveal mostly Ti and Ca lines, and an unusually red color arising from strong depression of flux at rest wavelengths $<5000$ AA. To date, this is the only reported SN showing Ti-dominated spectra. The data are broadly consistent with existing models for the pure detonation of a helium shell around a low-mass CO white dwarf and double-detonation models that include a secondary detonation of a CO core following a primary detonation in an overlying helium shell.
The detonation of a helium shell on top of a carbon-oxygen white dwarf has been argued as a potential explosion mechanism for type Ia supernovae (SNe~Ia). The ash produced during helium shell burning can lead to light curves and spectra that are inco
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We explore the evolution of thermonuclear supernova explosions when the progenitor white dwarf star ignites asymmetrically off-center. Several numerical simulations are carried out in two and three dimensions to test the consequences of different ini
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Early observations of Type Ia supernovae (SNe$,$Ia) provide essential clues for understanding the progenitor system that gave rise to the terminal thermonuclear explosion. We present exquisite observations of SN$,$2019yvq, the second observed SN$,$Ia
, after iPTF$,$14atg, to display an early flash of emission in the ultraviolet (UV) and optical. Our analysis finds that SN$,$2019yvq was unusual, even when ignoring the initial flash, in that it was moderately underluminous for an SN$,$Ia ($M_g approx -18.5,$mag at peak) yet featured very high absorption velocities ($v approx 15,000,mathrm{km,s}^{-1}$ for Si II $lambda$6355 at peak). We find that many of the observational features of SN$,$2019yvq, aside from the flash, can be explained if the explosive yield of radioactive $^{56}mathrm{Ni}$ is relatively low (we measure $M_{^{56}mathrm{Ni}} = 0.31 pm 0.05,M_odot$) and it and other iron-group elements are concentrated in the innermost layers of the ejecta. To explain both the UV/optical flash and peak properties of SN$,$2019yvq we consider four different models: interaction between the SN ejecta and a nondegenerate companion, extended clumps of $^{56}mathrm{Ni}$ in the outer ejecta, a double-detonation explosion, and the violent merger of two white dwarfs. Each of these models has shortcomings when compared to the observations; it is clear additional tuning is required to better match SN$,$2019yvq. In closing, we predict that the nebular spectra of SN$,$2019yvq will feature either H or He emission, if the ejecta collided with a companion, strong [Ca II] emission, if it was a double detonation, or narrow [O I] emission, if it was due to a violent merger.
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