The physical mechanism behind normal and peculiar Supernovae Ia and nuclear burning in Collapsar accretion disks

TYPEAstrophysics Seminar
Speaker:Yossef Zenati
Time:14:30 - 15:30
LocationZoom LINK
Remark:Ph.D seminar
Supernovae (SNe) are some of the most energetic explosions in the universe and are thought to arise either from the core collapse of massive stars or from the thermonuclear explosions of white dwarfs (WDs). Heavy elements such as nickel and iron, and intermediate elements such as sulfur, calcium, and titanium are all thought to form mainly through explosive nucleosynthetic processes occurring in the high-temperature, high-density environments in exploding cores of massive stars and WDs. A particularly important class of SNe are Type Ia SNe (SNe Ia), in which no hydrogen and no helium are observed, but for which strong silicon absorption lines are evident. The majority of SNe Ia show very similar light curve evolution, and similar spectral properties and are thought to arise from the thermonuclear explosions of WDs. The peak luminosity and the typical light curve width of standard type-Ia SNe are correlated, and after appropriate normalization, serve as the best standardizable candles available for measurement of large cosmological distances in the universe. The last two decades of observational progress in the advent and development of large-scale automated SNe surveys have revealed the existence of several families of non-standard type Ia and other likely thermonuclear. Here we focused on merging Neutron star (NS)-WD binaries as they come into contact. We examined their formation, as well as on the evolution of binary systems that could end as supernovae, and in particular, those containing Carbon Oxygen-WD (CO WDs) or HeCO WDs (hybrid WDs-are defined some specified fraction of he4 fractions in the range 6-20% of their mass and CO core). These SNe show distinct properties that separate them from normal SNe Ia, luminosity, LC (rapidly/slowly evolving), peculiar spectra, and/or environment (old/young, a different delay time distribution (DTD)). Many of these peculiar SNe can be classified into several distinct groups, and the estimated rates of SNe from each of these groups lead to the conclusion that they are relatively common transients.
The core collapse of massive, rapidly-rotating stars are thought to be the progenitors of long-duration gamma-ray bursts (GRB) and their associated hyper-energetic supernovae. Here we explore the effects of nuclear burning on collapsar accretion disks and their outflows by means of hydrodynamical alpha-viscosity torus simulations coupled to a 19-isotope nuclear reaction network, which are designed to mimic the late infall epochs in collapsar evolution when the viscous time of the torus has become comparable to the envelope fall-back time.  Our results address several key questions, such as the conditions for quiescent burning and accretion versus detonation and the generation of Ni56 in disk outflows, which may contribute to powering GRB supernovae. Being located in the slowest, innermost layers of the ejecta, the latter could provide the radioactive heating source necessary to make the spectral signatures of r-process elements visible in late-time GRB-SNe spectra.