arXiv subjects

Nahliel Wygoda

Publications and source records attributed to Nahliel Wygoda.

6 recordsLinked to original sources

arXiv2025

All known Type Ia supernovae models fail to reproduce the observed bolometric luminosity-width correlation

Type Ia supernovae (SNe Ia) are widely believed to arise from thermonuclear explosions of white dwarfs (WDs). However, ongoing debate surrounds their progenitor systems and the mechanisms triggering these explosions. Recently, Sharon \& Kushnir showed that existing models do not reproduce the observed positive correlation between the $γ$-ray escape time, $t_0$, and the synthesized $^{56}$Ni mass, $M_\mathrm{Ni56}$. Their analysis, while avoiding complex radiation transfer (RT) calculations, did not account for the viewing-angle dependence of the derived $t_0$ and $M_\mathrm{Ni56}$ in multi-dimensional (multi-D) models during pre-nebular phases, where most observations performed. Here, we aim to identify an observational width-luminosity relation, similar to the $t_0$-$M_\mathrm{Ni56}$ relation to constrain multi-D models during pre-nebular phases while minimizing RT calculation uncertainties. We show that the bolometric luminosity at $t\le30$ days since explosion can be accurately computed without non-thermal ionization considerations, which are computationally expensive and uncertain. We find that the ratio of the bolometric luminosity at 30 days since explosion to the peak luminosity, $L_{30}/Lp$, correlates strongly with $t_0$. Using a sample of well-observed SNe Ia, we show that this parameter tightly correlates with the peak luminosity, $L_p$. We compare the observed $L_{30}/Lp$-$L_p$ distribution with models from the literature, including non-spherical models consisting of head-on WD collisions and off-centered ignitions of sub-Chandrasekhar mass WDs. We find that all known SNe Ia models fail to reproduce the observed bolometric luminosity-width correlation.

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arXiv2023

StaNdaRT: A repository of standardized test models and outputs for supernova radiative transfer

We present the first results of a comprehensive supernova (SN) radiative-transfer (RT) code-comparison initiative (StaNdaRT), where the emission from the same set of standardized test models is simulated by currently-used RT codes. A total of ten codes have been run on a set of four benchmark ejecta models of Type Ia supernovae. We consider two sub-Chandrasekhar-mass ($M_\mathrm{tot} = 1.0$ M$_\odot$) toy models with analytic density and composition profiles and two Chandrasekhar-mass delayed-detonation models that are outcomes of hydrodynamical simulations. We adopt spherical symmetry for all four models. The results of the different codes, including the light curves, spectra, and the evolution of several physical properties as a function of radius and time, are provided in electronic form in a standard format via a public repository. We also include the detailed test model profiles and several python scripts for accessing and presenting the input and output files. We also provide the code used to generate the toy models studied here. In this paper, we describe in detail the test models, radiative-transfer codes and output formats and provide access to the repository. We present example results of several key diagnostic features.

astro-ph.SR↗

arXiv2020

Sub-Chandrasekhar-mass detonations are in tension with the observed $t_0-M_\text{Ni56}$ relation of type Ia supernovae

Type Ia supernovae (SNe Ia) are likely the thermonuclear explosions of carbon-oxygen (CO) white-dwarf (WD) stars, but their progenitor systems remain elusive. Recent studies have suggested that a propagating detonation within a thin helium shell surrounding a sub-Chandrasekhar mass CO core can subsequently trigger a detonation within the core (the double-detonation model, DDM). The outcome of this explosion is similar to a central ignition of a sub-Chandrasekhar mass CO WD (SCD). While SCD is consistent with some observational properties of SNe Ia, several computational challenges prohibit a robust comparison to the observations. We focus on the observed $t_0-M_\text{Ni56}$ relation, where $t_0$ (the $γ$-rays' escape time from the ejecta) is positively correlated with $M_\text{Ni56}$ (the synthesized $^{56}$Ni mass). We apply our recently developed numerical scheme to calculate SCD and show that the calculated $t_0-M_\text{Ni56}$ relation, which does not require radiation transfer calculations, converges to an accuracy of a few percent. We find a clear tension between our calculations and the observed $t_0-M_\text{Ni56}$ relation. SCD predicts an anti-correlation between $t_0$ and $M_\text{Ni56}$, with $t_0\approx30\,\textrm{day}$ for luminous ($M_\text{Ni56}\gtrsim0.5\,M_{\odot}$) SNe Ia, while the observed $t_0$ is in the range of $35-45\,\textrm{day}$. We show that this tension is larger than the uncertainty of the results, and that it exists in all previous studies of the problem. Our results hint that more complicated models are required, but we argue that DDM is unlikely to resolve the tension with the observations.

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arXiv2019

Type Ia supernovae have two physical width-luminosity relations and they favor sub-Chandrasekhar and direct collision models. I. Bolometric

While the width-luminosity relation (WLR) among type Ia supernovae (slower is brighter) has been extensively studied, its physical basis has not been convincingly identified. In particular, the 'width' has not been quantitatively linked yet to a physical time scale. We demonstrate that there are two robust fundamental time scales that 1. can be calculated based on integral quantities of the ejecta, with little dependence on radiation transfer modeling and 2. can be inferred from observations. The first is the gamma-ray escape time $t_0$, which determines the long-term evolution of the bolometric light curve and is studied in this Paper I. The second is the recombination time of $^{56}$Fe and $^{56}$Co, which sets the long-term color evolution of the emitted light and is studied in Paper II. Here we show that the gamma-ray escape time $t_0$ can be derived with $\sim 15\%$ accuracy from bolometric observations based on first principles. When applied to a sample of supernovae, the observed values of $t_0$ span a narrow range of $30-45$ days for the wide range of observed $^{56}\rm Ni$ masses $0.1M_{\odot}\lesssim M_{^{56}\rm Ni}\lesssim 1 M_{\odot}$. %This (trivial) bolometric WLR This narrow range of the gamma-ray escape time across the range of luminosities (a trivial WLR) is consistent with central detonations and direct collisions of sub-Chandrasekhar mass white dwarfs (WDs) but not with delayed detonation models for explosions of Chandrasekhar mass WDs, which are therefore disfavored as the primary channel for the population of type Ia supernovae. Computer codes for extracting $t_0$ from observations and models and for calculating gamma-ray transfer in 1D-3D are provided.

astro-ph.HE↗

arXiv2019

Type Ia supernovae have two physical width-luminosity relations and they favor sub-Chandrasekhar and direct collision models - II. Color evolution

While the width-luminosity relation (WLR) among type Ia supernovae (slower is brighter) is one of the best studied properties of this type of events, its physical basis has not been identified convincingly. The 'luminosity' is known to be related to a clear physical quantity -- the amount of $^{56}$Ni synthesized, but the 'width' has not been quantitatively linked yet to a physical time scale. We show that the recombination time of $^{56}$Fe and $^{56}$Co from doubly to singly ionized states causes the typical observed break in the color curve B-V due to a cliff in the mean opacities, and is a robust width measure of the light curve, which is insensitive to radiation transfer uncertainties. A simple photospheric model is shown to predict the recombination time to an accuracy of $\sim5$ days, allowing a quantitative understanding of the color WLR. Two physical times scales of the width luminosity relation are shown to be set by two column densities -- the total column density which sets the gamma-ray escape time $t_0$ (previous Paper I) and the $^{56}$Ni column density which sets the recombination time (this Paper II). Central detonations of sub-$\rm M_{ch}$ WDs and direct WD collision models have gamma-ray escape times and recombination times which are consistent with observations across the luminosity range of type Ia's. Delayed detonation Chandrasekhar mass models have recombination times that are broadly consistent with observations, with tension at the bright end of the luminosity range and inconsistent gamma-ray escape times at the faint end.

astro-ph.HE↗

arXiv2015

The energy budget of GRBs based on updated prompt \& afterglow observations

We compare the isotropic equivalent 15-2000 keV gamma-ray energy, E_gamma, emitted by a sample of 91 swift Gamma-Ray Bursts (GRBs) with known redshifts, with the isotropic equivalent fireball energy, E_fb, as estimated within the fireball model framework from X-ray afterglow observations of these bursts. The uncertainty in E_gamma, which spans the range of ~10^51 erg to ~10^53.5 erg, is approximately 25% on average, due mainly to the extrapolation from the BAT detector band to the 15-2000 keV band. The uncertainty in E_fb is approximately a factor of 2, due mainly to the X-ray measurements' scatter. We find E_gamma and E_fb to be tightly correlated. The average(std) of η^11hr_gamma is approximately log_10(E_gamma/(3ε _eE^11hr_fb)) are -0.34(0.60), and the upper limit on the intrinsic spread of η_gamma is approximately 0.5 (ε_e is the fraction of shocked plasma energy carried by electrons and E^x hr_fb is inferred from the X-ray flux at x hours). We also find that E_fb inferred from X-ray observations at 3 and 11 hours are similar, with an average(std) of log_10(E^3hr_fb/E^11hr_fb) of 0.04(0.28). The small variance of η_gamma implies that burst-to-burst variations in ε_e and in the efficiency of fireball energy conversion to gamma-rays are small, and suggests that both are of order unity. The small variance of η_gamma and the similarity of E^3hr_fb and E^11hr_fb further imply that ε_e does not vary significantly with shock Lorentz factor, and that for most bursts the modification of fireball energy during the afterglow phase, by processes such as radiative losses or extended duration energy injection, are not significant. Finally, our results imply that if fireballs are indeed jets, then the jet opening angle satisfies θ>0.1 for most cases. [abridged]

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