arXiv subjects

E. Bravo

Publications and source records attributed to E. Bravo.

At least 19 recordsLinked to original sources

arXiv2026

Will a Supernova explode in CD-30{\deg}11223?

Context: Accretion of He-rich matter onto a low mass carbon-oxygen white dwarf in a binary system with a He-rich donor may lead to an explosive event of Supernova Ia proportion, though with low peak luminosity and peculiar nucleosynthesis. Recently such a statement has been questioned, suggesting that, if the effects of rotation are accounted for in the evolution of the accretor, the latter does not explode, but it becomes a white dwarf with a massive He-buffer. Aims: We investigate the expected evolution of the currently detached binary CD-30{\deg}11223 harboring a 0.74 Msun carbon-oxygen white dwarf and a 0.47 Msun donor with a He-burning core and a very thin H-envelope (Delta M_H=6e-4 Msun). Methods: We use stellar the evolution code FuNS to compute the evolution of CD-30{\deg}11223. With respect to our earlier study of the system PTF J2238+743015.1, we include also the transport of angular momentum due to magnetic instabilities in the accretor interiors (``magnetic model''). Results: During the H-accretion phase, the effects of rotation in the accretor are negligible. In the ``magnetic model'', the angular momentum deposited by the accreted matter is very efficiently redistributed along the whole WD due to magnetic instabilities, so that the angular velocity of the accreted layers remains very low. During the He-accretion phase, the accretor experiences two very strong He-flashes which result in the ejection from the binary system of a large part of the matter previously accreted. The system ends its life as a carbon-oxygen core capped by a massive He/C/O-envelope (Delta M_{env} ~ 0.194 Msun) and an extremely low-mass companion, remnant of the donor. Conclusions: The system CD-30{\deg}11223 cannot be regarded as the potential progenitor of Supernova Ia. Such a conclusion applies also to all detached binary systems having similar masses of components and orbital periods.

astro-ph.SR↗

arXiv2026

Implications for Type Ia Supernova Nucleosynthesis from an Experimentally Constrained $^{16}$O$(p,\alpha)^{13}$N Reaction Rate

The $^{16}$O$(p,\alpha)^{13}$N reaction plays a key role in shaping the $\alpha$-particle abundance during explosive oxygen burning in Type Ia supernovae. By enhancing $\alpha$-production, this reaction directly affects the calcium-to-sulphur (Ca/S) and argon-to-sulphur (Ar/S) ratios, which serves as a tracer of progenitor metallicity. However, recent work suggests that the rate must be enhanced by a factor of up to seven over the standard value to explain observed Ca/S ratios across a range of progenitor metallicities. To explore this impact, available experimental cross-section data for the $^{16}$O$(p,\alpha)^{13}$N reaction have been compiled and critically evaluated. Significant discrepancies are identified in the low-energy region ($E_{\mathrm{cm}}$ = 5.7--7.0 MeV), primarily due to limitations of the activation method. To resolve this, the first direct measurement at astrophysical energies has been performed using the MUSIC active-target detector. The new $^{16}$O$(p,\alpha)^{13}$N thermonuclear reaction rate is found to be approximately 1.5 times higher than the REACLIB rate in the temperature range T = 3--4 GK, with more constrained uncertainties that resolve the previously large spread among existing data. The suggested factor of seven enhancement is excluded and these results indicate that this reaction alone cannot fully explain the variation in the Ca/S and Ar/S ratios observed across different progenitor metallicities. Therefore, future work should focus on reducing the uncertainties in other key oxygen-burning reactions, particularly $^{16}$O+$^{16}$O and $^{12}$C+$^{16}$O. Further reducing the constraints on the $^{16}$O$(p,\alpha)^{13}$N rate is also needed to fully determine to whether a nuclear physics solution to this discrepancy is possible.

nucl-ex↗

arXiv2024

Type Ia supernovae from chemically segregated white dwarfs

Type Ia supernovae are the outcome of the explosion of a carbon-oxygen white dwarf in a close binary system. They are thought to be the main contributors to the galactic nucleosynthesis of iron-peak elements, with important contributions to the yields of intermediate mass elements. Recent analyses of the phase diagram of carbon and oxygen containing impurities such as $^{22}$Ne and $^{56}$Fe in conditions relevant to white dwarf interiors suggest that both isotopes can partially separate when the temperature of the star is low enough to start solidifying. The purpose of this paper is to examine the impact of such a segregation on the yields of the different chemical species synthesized during explosions. A one-dimensional supernova code has been used to evaluate the impact of the sedimentation assuming different degrees of chemical separation. It is found that the main properties of the ejecta, kinetic energy and ejected mass of $^{56}$Ni do only vary slightly when the separation is taken into account. However, the yields of important isotopes that are used as diagnostic tools such as manganese can be strongly modified. Furthermore, the chemical segregation studied here is able to change several indicators related to progenitor metallicity (such as the mass ratio of calcium to sulphur in the ejecta or the UV flux of the supernova) and to its mass, whether it is a Chandrasekhar-mass white dwarf or a substantially lighter one (such as the imprint of stable nickel on late-time infrared spectra or those related to the presence of radioactive nickel at the centre of the ejecta).

astro-ph.SR↗

arXiv2021

Synthesis of radioactive elements in novae and supernovae and their use as a diagnostic tool

Novae and supernovae play a key role in many fields of Astrophysics and Cosmology. Despite their importance, an accurate description of which objects explode and why and how they explode is still lacking. One of the main characteristics of such explosions is that they are the main suppliers of newly synthesized chemical elements in the Galaxy. Since some of these isotopes are radioactive, it is possible to use the corresponding gamma-rays as a diagnostic tool of the explosion thanks to their independence on the thermal state of the debris. The drawback is the poor sensitivity of detectors in the MeV energy domain. As a consequence, the radioactive lines have only been detected in one core collapse supernova (SN 1987A), one Type Ia supernova (SN 2014J), and one supernova remnant (Cas A). Nevertheless these observations have provided and are providing important information about the explosion mechanisms. Unfortunately, novae are still eluding detection. These results emphasize the necessity to place as soon as possible a new instrument in orbit with enough sensitivity to noticeably enlarge the sample of detected events

astro-ph.HE↗

arXiv2018

White Dwarf Collisions, a promising scenario to account for meteoritic anomalies

It is commonly accepted that collisions between white dwarfs (WD) are rare events that only occur in the dense interior of globular clusters or in the dense outskirts around the central galactic black holes, and are therefore disregarded as an important source of Type Ia supernovae (SNIa). Although the majority of these encounters will not result in a SNIa event, many of them will produce mass ejections. Under the appropriate circumstances, this material can become part of a protostar nebula, including the pre-solar one, in the form of stardust leading to the existence of chemical anomalies in meteorites. We describe a WD-WD collision scenario that potentially might explain the so called Ne-E anomaly found in some primitive meteorites like Orgueil and Murchison.

astro-ph.SR↗

arXiv2017

Gamma-rays from SNIa

Type Ia supernovae are thought to be the outcome of the thermonuclear explosion of a carbon/oxygen white dwarf in a close binary system. Their optical light curve is powered by thermalized gamma-rays produced by the radioactive decay of 56Ni, the most abundant isotope present in the debris. The maximum and the shape of the light curve strongly depends on the total amount and distribution of this freshly synthesized isotope, as well as on the velocity and density distribution of the ejecta. Gamma-rays escaping the ejecta have the advantage of their lower interaction with the ejecta, the possibility to distinguish among isotopes and the relative simplicity of their transport modelling, and can be used as a diagnostic tool for studying the structure of the exploding star and the characteristics of the explosion, as it has been proved in the case of SN2014J.

astro-ph.GA↗

arXiv2017

Insights on the physics of SNIa obtained from their gamma-ray emission

Type Ia supernovae are thought to be the outcome of the thermonuclear explosion of a carbon/oxygen white dwarf in a close binary system. Their optical light curve is powered by thermalized gamma-rays produced by the radioactive decay of $^{56}$Ni, the most abundant isotope present in the debris. Gamma-rays escaping the ejecta can be used as a diagnostic tool for studying the structure of the exploding star and the characteristics of the explosion. The fluxes of the $^{56}$Ni lines and the continuum obtained by INTEGRAL from SN2014J in M82, the first ever gamma-detected SNIa, around the time of the maximum of the optical light curve strongly suggest the presence of a plume of $^{56}$Ni in the outermost layers moving at high velocities. If this interpretation was correct, it could have important consequences on our current understanding of the physics of the explosion and on the nature of the systems that explode.

astro-ph.HE↗

arXiv2017

Cobalt-56 gamma-ray emission lines from the type Ia supernova 2014J

A type Ia supernova is thought to be a thermonuclear explosion of either a single carbon-oxygen white dwarf or of a pair of merging white dwarfs. The explosion fuses a large amount of radioactive 56Ni. After the explosion, the decay chain from 56Ni to 56Co to 56Fe generates gamma-ray photons, which are reprocessed in the expanding ejecta and give rise to powerful optical emission. Here we report the detection of 56Co lines at energies of 847 and 1238 keV and a gamma-ray continuum in the 200-400 keV band from the type Ia supernova 2014J in the nearby galaxy M82. The line fluxes suggest that about 0.6 +/- 0.1 solar masses of radioactive 56Ni were synthesized during the explosion. The line broadening gives a characteristic mass-weighted ejecta expansion velocity of 10000 +/- 3000 km/s. The observed gamma-ray properties are in broad agreement with the canonical model of an explosion of a white dwarf just massive enough to be unstable to gravitational collapse, but do not immediately exclude more complicated merger scenarios, which fuse comparable amount of 56Ni.

astro-ph.HE↗

arXiv2016

Explosion of white dwarfs harboring hybrid CONe cores

Recently, it has been found that off-centre carbon burning in a subset of intermediate-mass stars does not propagate all the way to the center, resulting in a class of hybrid CONe cores. Here, we consider the possibility that stars hosting these hybrid CONe cores might belong to a close binary system and, eventually, become white dwarfs accreting from a non-degenerate companion at rates leading to a supernova explosion. We have computed the hydrodynamical phase of the explosion of Chandrasekhar-mass white dwarfs harboring hybrid cores, assuming that the explosion starts at the center, either as a detonation (as may be expected in some degenerate merging scenarios) or as a deflagration (that afterwards transitions into a delayed detonation). We assume these hybrid cores are made of a central CO volume, of mass M(CO), surrounded by an ONe shell. We show that, in case of a pure detonation, a medium-sized CO-rich region, M(CO)<0.4 Msun, results in the ejection of a small fraction of the mantle while leaving a massive bound remnant. Part of this remnant is made of the products of the detonation, Fe-group nuclei, but they are buried in its inner regions, unless convection is activated during the ensuing cooling and shrinking phase of the remnant. In contrast, and somehow paradoxically, delayed detonations do not leave remnants but for the minimum M(CO) we have explored, M(CO)=0.2 Msun, and even in this case the remnant is as small as 0.13 Msun. The ejecta produced by these delayed detonations are characterized by slightly smaller masses of 56Ni and substantially smaller kinetic energies than obtained for a delayed detonation of a 'normal' CO white dwarf. The optical emission expected from these explosions would hardly match the observational properties of typical Type Ia supernovae, although they make interesting candidates for the subluminous class of SN2002cx-like or SNIax.

astro-ph.SR↗

arXiv2016

Gamma-Ray emission from SN2014J near maximum optical light

The optical light curve of Type Ia supernovae (SNIa) is powered by thermalized gamma-rays produced by the decay of 56Ni and 56Co, the main radioactive isotopes synthesized by the thermonuclear explosion of a C/O white dwarf. Gamma-rays escaping the ejecta can be used as a diagnostic tool for studying the characteristics of the explosion. In particular, it is expected that the analysis of the early gamma emission, near the maximum of the optical light curve, could provide information about the distribution of the radioactive elements in the debris. In this paper, the gamma data obtained from SN2014J in M82 by the instruments on board of INTEGRAL are analyzed taking special care of the impact that the detailed spectral response has on the measurements of the intensity of the lines. The 158 keV emission of 56Ni has been detected in SN2014J at ~5 sigma at low energy with both ISGRI and SPI around the maximum of the optical light curve. After correcting the spectral response of the detector, the fluxes in the lines suggest that, in addition to the bulk of radioactive elements buried in the central layers of the debris, there is a plume of 56Ni, with a significance of ~3 sigma, moving at high velocity and receding from the observer. The mass of the plume is in the range of ~ 0.03-0.08 solar masses. No SNIa explosion model had predicted the mass and geometrical distribution of 56Ni suggested here. According to its optical properties, SN2014J looks as a normal SNIa. So it is extremely important to discern if it is also representative in the gamma-ray band.

astro-ph.HE↗

arXiv2015

Gamma-rays from Type Ia supernova SN2014J

The whole set of INTEGRAL observations of type Ia supernova SN2014J, covering the period 19-162 days after the explosion has being analyzed. For spectral fitting the data are split into "early" and "late" periods covering days 19-35 and 50-162, respectively, optimized for $^{56}$Ni and $^{56}$Co lines. As expected for the early period much of the gamma-ray signal is confined to energies below $\sim$200 keV, while for the late period it is most strong above 400 keV. In particular, in the late period $^{56}$Co lines at 847 and 1248 keV are detected at 4.7 and 4.3 $σ$ respectively. The lightcurves in several representative energy bands are calculated for the entire period. The resulting spectra and lightcurves are compared with a subset of models. We confirm our previous finding that the gamma-ray data are broadly consistent with the expectations for canonical 1D models, such as delayed detonation or deflagration models for a near-Chandrasekhar mass WD. Late optical spectra (day 136 after the explosion) show rather symmetric Co and Fe lines profiles, suggesting that unless the viewing angle is special, the distribution of radioactive elements is symmetric in the ejecta.

astro-ph.HE↗

arXiv2014

Measurement of the $^{58}$Ni($α$,$γ$)$^{62}$Zn reaction and its astrophysical impact

Cross section measurements of the $^{58}$Ni($α$,$γ$)$^{62}$Zn reaction were performed in the energy range $E_α=5.5-9.5$ MeV at the Nuclear Science Laboratory of the University of Notre Dame, using the NSCL Summing NaI(Tl) detector and the $γ$-summing technique. The measurements are compared to predictions in the statistical Hauser-Feshbach model of nuclear reactions using the SMARAGD code. It is found that the energy dependence of the cross section is reproduced well but the absolute value is overestimated by the prediction. This can be remedied by rescaling the $α$ width by a factor of 0.45. Stellar reactivities were calculated with the rescaled $α$ width and their impact on nucleosynthesis in type Ia supernovae has been studied. It is found that the resulting abundances change by up to 5\% when using the new reactivities.

nucl-ex↗

arXiv2013

Observations of SN2011fe with INTEGRAL

SN2011fe was detected by the Palomar Transient Factory on August 24th 2011 in M101 few hours after the explosion. From the early spectra it was immediately realized that it was a Type Ia supernova thus making this event the brightest one discovered in the last twenty years. In this paper the observations performed with the instruments on board of INTEGRAL (SPI, IBIS/ISGRI, JEM-X and OMC) before and after the maximum of the optical light as well as the interpretation in terms of the existing models of $γ$--ray emission from such kind of supernovae are reported. All INTEGRAL high-energy have only been able to provide upper limits to the expected emission due to the decay of $^{56}$Ni. These bounds allow to reject explosions involving a massive white dwarf in the sub--Chandrasekhar scenario. On the other hand, the optical light curve obtained with the OMC camera suggests that the event was produced by a delayed detonation of a CO white dwarf that produced $\sim 0.5$ M$\odot$ of $^{56}$Ni. In this particular case, INTEGRAL would have only been able to detect the early $γ$--ray emission if the supernova had occurred at a distance of 2 -3 Mpc, although the brightest event could be visible up to distances larger by a factor two.

astro-ph.HE↗

arXiv2013

Observation of SN2011fe with INTEGRAL. I. Pre--maximum phase

SN2011fe was detected by the Palomar Transient Factory on August 24th 2011 in M101 a few hours after the explosion. From the early optical spectra it was immediately realized that it was a Type Ia supernova thus making this event the brightest one discovered in the last twenty years. The distance of the event offered the rare opportunity to perform a detailed observation with the instruments on board of INTEGRAL to detect the gamma-ray emission expected from the decay chains of $^{56}$Ni. The observations were performed in two runs, one before and around the optical maximum, aimed to detect the early emission from the decay of $^{56}$Ni and another after this maximum aimed to detect the emission of $^{56}$Co. The observations performed with the instruments on board of INTEGRAL (SPI, IBIS/ISGRI, JEMX and OMC) have been analyzed and compared with the existing models of gamma-ray emission from such kind of supernovae. In this paper, the analysis of the gamma-ray emission has been restricted to the first epoch. Both, SPI and IBIS/ISGRI, only provide upper-limits to the expected emission due to the decay of $^{56}$Ni. These upper-limits on the gamma-ray flux are of 7.1 $\times$ 10$^{-5}$ ph/s/cm$^2$ for the 158 keV line and of 2.3 $\times$ 10$^{-4}$ ph/s/cm$^2$ for the 812 keV line. These bounds allow to reject at the $2σ$ level explosions involving a massive white dwarf, $\sim 1$ M$\odot$ in the sub--Chandrasekhar scenario and specifically all models that would have substantial amounts of radioactive $^{56}$Ni in the outer layers of the exploding star responsible of the SN2011fe event. The optical light curve obtained with the OMC camera also suggests that SN2011fe was the outcome of the explosion, possibly a delayed detonation although other models are possible, of a CO white dwarf that synthesized $\sim 0.55$ M$_\odot$ of $^{56}$Ni. For this specific model.

astro-ph.HE↗

arXiv2012

Insights into thermonuclear supernovae from the incomplete silicon burning process

Type Ia supernova (SNIa) explosions synthesize a few tenths to several tenths of a solar mass, whose composition is the result of incomplete silicon burning that reaches peak temperatures of 4 GK to 5 GK. The elemental abundances are sensitive to the physical conditions in the explosion, making their measurement a promising clue to uncovering the properties of the progenitor star and of the explosion itself. Using a parameterized description of the thermodynamic history of matter undergoing incomplete silicon burning, we computed the final composition for a range of parameters wide enough to encompass current models of SNIa. Then, we searched for combinations of elemental abundances that trace the parameters values and are potentially measurable. For this purpose, we divide the present study into two epochs of SNIa, namely the optical epoch, from a few weeks to several months after the explosion, and the X-ray epoch, which refers to the time period in which the supernova remnant is young, starting one or two hundred years age and ending a thousand years after the event. During the optical epoch, the only SNIa property that can be extracted from the detection of incomplete silicon burning elements is the neutron excess of the progenitor white dwarf at thermal runaway, which can be determined through measuring the ratio of the abundance of manganese to that of titanium, chromium, or vanadium. Conversely, in the X-ray epoch, any abundance ratio built using a couple of elements from titanium, vanadium, chromium, or manganese may constrain the initial neutron excess. Furthermore, measuring the ratio of the abundances of vanadium to manganese in the X-ray might shed light on the timescale of the thermonuclear explosion.

astro-ph.SR↗

arXiv2011

Type Ia supernovae and the ^{12}C+^{12}C reaction rate

The experimental determination of the cross-section of the ^{12}C+^{12}C reaction has never been made at astrophysically relevant energies (E<2 MeV). The profusion of resonances throughout the measured energy range has led to speculation that there is an unknown resonance at E\sim1.5 MeV possibly as strong as the one measured for the resonance at 2.14 MeV. We study the implications that such a resonance would have for the physics of SNIa, paying special attention to the phases that go from the crossing of the ignition curve to the dynamical event. We use one-dimensional hydrostatic and hydrodynamic codes to follow the evolution of accreting white dwarfs until they grow close to the Chandrasekhar mass and explode as SNIa. In our simulations, we account for a low-energy resonance by exploring the parameter space allowed by experimental data. A change in the ^{12}C+^{12}C rate similar to the one explored here would have profound consequences for the physical conditions in the SNIa explosion, namely the central density, neutronization, thermal profile, mass of the convective core, location of the runaway hot spot, or time elapsed since crossing the ignition curve. For instance, with the largest resonance strength we use, the time elapsed since crossing the ignition curve to the supernova event is shorter by a factor ten than for models using the standard rate of ^{12}C+^{12}C, and the runaway temperature is reduced from \sim8.14\times10^{8} K to \sim4.26\times10^{8} K. On the other hand, a resonance at 1.5 MeV, with a strength ten thousand times smaller than the one measured at 2.14 MeV, but with an α/p yield ratio substantially different from 1 would have a sizeable impact on the degree of neutronization of matter during carbon simmering. We conclude that a robust understanding of the links between SNIa properties and their progenitors will not be attained until the ^{12}C+^{12}C reaction rate is measured at energies \sim1.5 MeV.

astro-ph.SR↗

arXiv2010

Metallicity as a source of dispersion in the SNIa bolometric light curve luminosity-width relationship

The recognition that the metallicity of Type Ia supernova (SNIa) progenitors might bias their use for cosmological applications has led to an increasing interest in its role on the shaping of SNIa light curves. We explore the sensitivity of the synthesized mass of 56Ni, M(56Ni), to the progenitor metallicity starting from Pre-Main Sequence models with masses M0 = 2 - 7 M_sun and metallicities Z = 1e-5 - 0.10. The interplay between convective mixing and carbon burning during the simmering phase eventually rises the neutron excess and leads to a smaller 56Ni yield, but does not change substantially the dependence of M(56Ni) on Z. Uncertain attributes of the WD, like the central density, have a minor effect on M(56Ni). Our main results are: 1) a sizable amount of 56 Ni is synthesized during incomplete Si-burning, which leads to a stronger dependence of M(56Ni) on Z than obtained by assuming that 56Ni is produced in material that burns fully to nuclear statistical equilibrium; 2) in one-dimensional delayed detonation simulations a composition dependence of the deflagration-to-detonation transition density gives a non-linear relationship between M(56Ni) and Z, and predicts a luminosity larger than previously thought at low metallicities (however, the progenitor metallicity alone cannot explain the whole observational scatter of SNIa luminosities), and 3) an accurate measurement of the slope of the Hubble residuals vs metallicity for a large enough data set of SNIa might give clues to the physics of deflagration-to-detonation transition in thermonuclear explosions.

astro-ph.CO↗

arXiv2008

Axisymmetric smoothed particle hydrodynamics with self-gravity

The axisymmetric form of the hydrodynamic equations within the smoothed particle hydrodynamics (SPH) formalism is presented and checked using idealized scenarios taken from astrophysics (free fall collapse, implosion and further pulsation of a sun-like star), gas dynamics (wall heating problem, collision of two streams of gas) and inertial confinement fusion (ICF, -ablative implosion of a small capsule-). New material concerning the standard SPH formalism is given. That includes the numerical handling of those mass points which move close to the singularity axis, more accurate expressions for the artificial viscosity and the heat conduction term and an easy way to incorporate self-gravity in the simulations. The algorithm developed to compute gravity does not rely in any sort of grid, leading to a numerical scheme totally compatible with the lagrangian nature of the SPH equations.

astro-ph↗