arXiv subjects

M. Obergaulinger

Publications and source records attributed to M. Obergaulinger.

At least 19 recordsLinked to original sources

arXiv2025

Tracing the ejecta structure of SN 1987A: Insights and diagnostics from 3D MHD simulations

Supernova (SN) 1987A provides a unique window into the aftermath of a massive stellar explosion, offering key insights into the ejecta's morphology, composition, explosion mechanism, progenitor system, and circumstellar medium (CSM) interaction. We investigate large-scale ejecta asymmetries in SN 1987A. By comparing the simulations with JWST observations and making predictions for XRISM, we aim to refine our understanding of the explosion mechanism and the remnant's evolution. We performed 3D MHD simulations that trace the evolution of SN 1987A from the SN to the SNR, extending our predictions up to 5000 years into the future and considering the Ni-bubble effects. The simulation results are compared with JWST observations and used to predict XRISM spectra, to evaluate the accuracy of the modeled ejecta structure. Our simulations reproduce the large-scale Fe-rich ejecta morphology seen by JWST, revealing two clumps suggestive of a bipolar explosion. Ni-bubble effects in the first year boost Fe-rich ejecta expansion and their interaction with the reverse shock. However, discrepancies with JWST observations in clump velocities and spatial distribution suggest stronger explosion asymmetries than modeled. Since 2021, our models predict that shocked ejecta have contributed increasingly to X-ray emission, now rivaling shocked CSM and soon dominating as the latter fades. Future XRISM observations will trace the evolution of these ejecta structures, refining constraints on explosion geometry. Early remnant asymmetries from CSM interaction may persist for at least 100 years. Our results underscore the role of asymmetric core-collapse mechanisms in shaping SN 1987A's ejecta and constraining its explosion geometry. Future studies should explore more extreme asymmetries, in neutrino-driven core collapse or magneto-rotational SN models, to identify the origin of its bipolar Fe-rich structure.

astro-ph.HE↗

arXiv2024

Nucleosynthesis in magnetorotational supernovae: impact of the magnetic field configuration

The production of heavy elements is one of the main by-products of the explosive end of massive stars. A long sought goal is finding differentiated patterns in the nucleosynthesis yields, which could permit identifying a number of properties of the explosive core. Among them, the traces of the magnetic field topology are particularly important for \emph{extreme} supernova explosions, most likely hosted by magnetorotational effects. We investigate the nucleosynthesis of five state-of-the-art magnetohydrodynamic models with fast rotation that have been previously calculated in full 3D and that involve an accurate neutrino transport (M1). One of the models does not contain any magnetic field and synthesizes elements around the iron group, in agreement with other CC-SNe models in literature. All other models host a strong magnetic field of the same intensity, but with different topology. For the first time, we investigate the nucleosynthesis of MR-SNe models with a quadrupolar magnetic field and a 90 degree tilted dipole. We obtain a large variety of ejecta compositions reaching from iron nuclei to nuclei up to the third r-process peak. We assess the robustness of our results by considering the impact of different nuclear physics uncertainties such as different nuclear masses, $β^{-}$-decays and $β^{-}$-delayed neutron emission probabilities, neutrino reactions, fission, and a feedback of nuclear energy on the temperature. We find that the qualitative results do not change with different nuclear physics input. The properties of the explosion dynamics and the magnetic field configuration are the dominant factors determining the ejecta composition.

astro-ph.HE↗

arXiv2023

Inference of proto-neutron star properties in core-collapse supernovae from a gravitational-wave detector network

The next Galactic core-collapse supernova (CCSN) will be a unique opportunity to study within a fully multi-messenger approach the explosion mechanism responsible for the formation of neutron stars and stellar-mass black holes. State-of-the-art numerical simulations of those events reveal the complexity of the gravitational-wave emission which is highly stochastic. This challenges the possibility to infer the properties of the compact remnant and of its progenitor using the information encoded in the waveforms. In this paper we take further steps in a program we recently initiated to overcome those difficulties. In particular we show how oscillation modes of the proto-neutron star, highly visible in the gravitational-wave signal, can be used to reconstruct the time evolution of their physical properties. Extending our previous work where only the information from a single detector was used we here describe a new data-analysis pipeline that coherently combines gravitational-wave detectors' data and infers the time evolution of a combination of the mass and radius of the compact remnant. The performance of the method is estimated employing waveforms from 2D and 3D CCSN simulations covering a progenitor mass range between 11$\mathrm{M_{\odot}}$\, and 40$\mathrm{M_{\odot}}$\, and different equations of state for both a network of up to five second-generation detectors and the proposed third-generation detectors Einstein Telescope and Cosmic Explorer. Our study shows that it will be possible to infer PNS properties for CCSN events occurring in the vicinity of the Milky Way, up to the Large Magellanic Cloud, with the current generation of gravitational-wave detectors.

astro-ph.HE↗

arXiv2023

Nucleosynthesis in jet-driven and jet-associated supernovae

In contrast to regular core-collapse supernovae, explosions of rapidly rotating massive stars can develop jets, fast collimated outflows directed along the rotational axis. Depending on the rate of rotation and the magnetic field strength before collapse as well as on possible mechanisms amplifying the magnetic field, such a core can explode magnetorotationally rather than via the standard supernova mechanism based on neutrino heating. This scenario can explain the highest kinetic energies observed in the class of hypernovae. On longer time scales, rotation and magnetic fields can play an important role in the engine of long gamma-ray burst powered by proto-magnetars or hyperaccreting black holes in collapsars. Both classes of events are characterized by relativistic jets and winds driven by neutrinos or magnetic spin-down of the central objects. The nucleosynthesis in these events includes the production of Fe group elements, including a possibly enhanced synthesis of radioactive 56Ni leading to high peak luminosities. Additionally, these events are, out of all stellar core-collapse events the ones most likely to allow for the formation of the heaviest nuclei via rapid neutron captures. Increasingly sophisticated numerical simulations indicate that at least a limited r-process is possible, though it remains open how robust this result is against variations in the numerical methods and the initial conditions. If so, supernovae with jets could contribute to the observed galactic chemical enrichment, in particular at early times before neutron-star mergers might be able to set in.

astro-ph.HE↗

arXiv2022

Magnetorotational core collapse of possible GRB progenitors. IV. A wider range of progenitors

The final collapse of the cores of massive stars can lead to a wide variety of outcomes in terms of electromagnetic and kinetic energies, nucleosynthesis, and remnants. The connection of this wide spectrum of explosion and remnant types to the properties of the progenitors remains an open issue. Rotation and magnetic fields in Wolf-Rayet stars of subsolar metallicity may explain extreme events such as superluminous supernovae and gamma-ray bursts powered by proto-magnetars or collapsars. Continuing numerical studies of magnetorotational core collapse including detailed neutrino physics, we focus on progenitors with zero-age main-sequence masses in the range between 5 and 39 solar masses. The pre-collapse stars are one dimensional models employing prescriptions for the effects of rotation and magnetic fields. Eight of the ten stars we consider being the results of chemically homogeneous evolution due to enhanced rotational mixing (Aguilera-Dena et al. 2018). All but one of them produce explosions driven by neutrino heating (more likely for low mass progenitors up to 8 solar masses) and non-spherical flows or by magnetorotational stresses (more frequent above 26 solar masses). In most of them and for the one non-exploding model, ongoing accretion leads to black-hole formation. Rapid rotation makes a subsequent collapsar activity plausible. Models not forming black holes show proto-magnetar driven jets. Conditions for the formation of nickel are more favourable in magneto-rotationally driven models, though our rough estimates fall short of the requirements for extremely bright events if these are powered by radioactive decay. However, approximate light curves of our models suggest that a proto-magnetar or black hole spin-down may fuel luminous transients (with peak luminosities ~ 10^{43...44} erg).

astro-ph.HE↗

arXiv2021

Post-explosion evolution of core-collapse supernovae

We investigate the post-explosion phase in core-collapse supernovae with 2D hydrodynamical simulations and a simple neutrino treatment. The latter allows us to perform 46 simulations and follow the evolution of the 32 successful explosions during several seconds. We present a broad study based on three progenitors (11.2 $M_\odot$, 15 $M_\odot$, and 27 $M_\odot$), different neutrino-heating efficiencies, and various rotation rates. We show that the first seconds after shock revival determine the final explosion energy, remnant mass, and properties of ejected matter. Our results suggest that a continued mass accretion increases the explosion energy even at late times. We link the late-time mass accretion to initial conditions such as rotation strength and shock deformation at explosion time. Only some of our simulations develop a neutrino-driven wind that survives for several seconds. This indicates that neutrino-driven winds are not a standard feature expected after every successful explosion. Even if our neutrino treatment is simple, we estimate the nucleosynthesis of the exploding models for the 15 $M_\odot$ progenitor after correcting the neutrino energies and luminosities to get a more realistic electron fraction.

astro-ph.HE↗

arXiv2020

The impact of non-dipolar magnetic fields in core-collapse supernovae

The magnetic field is believed to play an important role in at least some core-collapse supernovae if its magnitude reaches $10^{15}\,\rm{G}$, which is a typical value for a magnetar. In the presence of fast rotation, such a strong magnetic field can drive powerful jet-like explosions if it has the large-scale coherence of a dipole. The topology of the magnetic field is, however, probably much more complex with strong multipolar and small-scale components and the consequences for the explosion are so far unclear. We investigate the effects of the magnetic field topology on the dynamics of core-collapse supernovae and the properties of forming proto-neutron star (PNS) by comparing pre-collapse fields of different multipolar orders and radial profiles. Using axisymmetric special relativistic MHD simulations and a two-moment neutrino transport, we find that higher multipolar magnetic configurations lead to generally less energetic explosions, slower expanding shocks and less collimated outflows. Models with a low order multipolar configuration tend to produce more oblate PNS, surrounded in some cases by a rotationally supported toroidal structure of neutron-rich material. Moreover, magnetic fields which are distributed on smaller angular scales produce more massive and faster rotating central PNS, suggesting that higher-order multipolar configurations tend to decrease the efficiency of the magnetorotational launching mechanism. Even if our dipolar models systematically display a far more efficient extraction of the rotational energy of the PNS, fields distributed on smaller angular scales are still capable of powering magnetorotational explosions and shape the evolution of the central compact object.

astro-ph.HE↗

arXiv2020

Magnetorotational core collapse of possible GRB progenitors. I. Explosion mechanisms

We investigate the explosion of stars with zero-age main-sequence masses between 20 and 35 solar masses and varying degrees of rotation and magnetic fields including ones commonly considered progenitors of gamma-ray bursts (GRBs). The simulations, combining special relativistic magnetohydrodynamics, a general relativistic approximate gravitational potential, and two-moment neutrino transport, demonstrate the viability of different scenarios for the post-bounce evolution. Having formed a highly massive proto-neutron star (PNS), several models launch successful explosions, either by the standard supernova mechanism based on neutrino heating and hydrodynamic instabilities or by magnetorotational processes. It is, however, quite common for the PNS to collapse to a black hole (BH) within a few seconds. Others might produce proto-magnetar-driven explosions. We explore several ways to describe the different explosion mechanisms. The competition between the timescales for advection of gas through the gain layer and heating by neutrinos provides an approximate explanation for models with insignificant magnetic fields. The fidelity of this explosion criterion in the case of rapid rotation can be improved by accounting for the strong deviations from spherical symmetry and mixing between pole and equator. We furthermore study an alternative description including the ram pressure of the gas falling through the shock. Magnetically driven explosions tend to arise from a strongly magnetised region around the polar axis. In these cases, the onset of the explosion corresponds to the equality between the advection timescale and the timescale for the propagation of Alfvén waves through the gain layer.

astro-ph.HE↗

arXiv2019

Titanium hidden in dust

Cassiopeia A, one of the most intriguing galactic supernova remnants, has been a target of many observational efforts including most recent observations by ALMA, Hubble, Herschel, Spitzer, NuSTAR, Integral, and other observatories. We use recent gamma-ray lines observations of the radioactive products of Cas A supernova explosive nucleosynthesis as well as spectral energy densities derived for Cas A at infrared wavelengths to speculate about the possibility of radioactive 44Ti being locked into large dust grains. This suggestion is also supported by the possible observation of a pre-supernova outburst about 80 years before the actual Cas A supernova explosion in 1671 AD by Italian astronomer G.D. Cassini. The plausibility of such a scenario is discussed also with reference to recent supernovae, and to the contribution of core-collapse supernovae to the overall dust production in the Galaxy.

astro-ph.HE↗

arXiv2019

Neutron star collapse and gravitational waves with a non-convex equation of state

The thermodynamical properties of the equation of state (EoS) of high-density matter (above nuclear saturation density) and the possible existence of exotic states such as phase transitions from nuclear/hadronic matter into quark-gluon plasma, or the appearance of hyperons, may critically influence the stability and dynamics of compact relativistic stars. From a theoretical point of view, establishing the existence of those states requires the analysis of the `convexity' of the EoS. We show indications of the existence of regions in the dense-matter EoS where the thermodynamics may be non-convex as a result of a non-monotonic dependence of the sound speed with the rest-mass density. When this happens, non-conventional dynamics may develop. In this paper we investigate the effects of a phenomenological, non-convex EoS on the equilibrium structure of stable compact stars and on the dynamics of unstable neutron stars that collapse gravitationally to black holes, both for spherically symmetric and uniformly-rotating configurations. We show how the dynamics of the collapse with a non-convex EoS departs from the convex case, leaving distinctive imprints on the gravitational waveforms. The astrophysical significance of these results for microphysical EoSs is discussed.

astro-ph.HE↗

arXiv2018

Core collapse with magnetic fields and rotation

We study the effects of magnetic fields and rotation on the core collapse of a star of an initial mass of M = 20 solar masses using axisymmetric simulations coupling special relativistic magnetohydrodynamics, an approximately relativistic gravitational potential, and spectral neutrino transport. We compare models of the same core with different, artificially added profiles of rotation and magnetic field. A model with weak field and slow rotation does not produce an explosion, while stronger fields and fast rotation open the possibility of explosions. Whereas the neutrino luminosities of the exploding models are the same as or even less than those of the non-exploding model, magnetic fields locally in equipartition with the gas pressure provide a strong contribution to the shock revival and the acceleration of bipolar outflows. Among the amplification processes generating such strong fields, we find the magneto-rotational instability. However, our limited grid resolution allows us to find it only in limited regions of the model with the strongest pre-collapse field ($10^{11}$ G) and fastest rotation.

astro-ph.HE↗

arXiv2018

On the existence of a luminosity threshold of GRB jets in massive stars

Motivated by the many associations of $γ$-ray bursts (GRBs) with energetic supernova (SN) explosions, we study the propagation of relativistic jets within the progenitor star in which a SN shock wave may be launched briefly before the jets start to propagate. Based on analytic considerations and verified with an extensive set of 2D axisymmetric relativistic hydrodynamic simulations, we have estimated a threshold intrinsic jet luminosity, $L_{\rm j}^{\rm thr}$, for successfully launching a jet. This threshold depends on the structure of the progenitor and, thus, it is sensible to its mass and to its metallicity. For a prototype host of cosmological long GRBs, a low-metallicity star of 35$\,M_{\odot}$, it is $L_{\rm j}^{\rm thr} \simeq 1.35\times 10^{49}\,$erg$\,$s$^{-1}$. The observed equivalent isotropic $γ$-ray luminosity, $L_{\rm γ,iso,BO} \simeq 4 ε_γL_{\rm j} θ_{\rm BO}^{-2}$, crucially depends on the jet opening angle after breakout, $θ_{\rm BO}$, and on the efficiency for converting the intrinsic jet luminosity into $γ$-radiation, $ε_γ$. Highly energetic jets can produce low-luminosity events if either their opening angle after the breakout is large, which is found in our models, or if the conversion efficiency of kinetic and internal energy into radiation is low enough. Beyond this theoretical analysis, we show how the presence of a SN shock wave may reduce this luminosity threshold by means of numerical simulations. We foresee that the high-energy transients released by jets produced near the luminosity threshold will be more similar to llGRBs or XRFs than to GRBs.

astro-ph.HE↗

arXiv2017

Estimation of the mechanical properties of the eye through the study of its vibrational modes

Measuring the eye's mechanical properties in vivo and with minimally invasive techniques can be the key for individualized solutions to a number of eye pathologies. The development of such techniques largely relies on a computational modelling of the eyeball and, it optimally requires the synergic interplay between experimentation and numerical simulation. In Astrophysics and Geophysics the remote measurement of structural properties of the systems of their realm is performed on the basis of (helio-)seismic techniques. As a biomechanical system, the eyeball possesses normal vibrational modes encompassing rich information about its structure and mechanical properties. However, the integral analysis of the eyeball vibrational modes has not been performed yet. Here we develop a new finite difference method to compute both the spheroidal and, specially, the toroidal eigenfrequencies of the human eye. Using this numerical model, we show that the vibrational eigenfrequencies of the human eye fall in the interval 100 Hz - 10 MHz. We find that compressible vibrational modes may release a trace on high frequency changes of the intraocular pressure, while incompressible normal modes could be registered analyzing the scattering pattern that the motions of the vitreous humour leave on the retina. Existing contact lenses with embebed devices operating at high sampling frequency could be used to register the microfluctuations of the eyeball shape we obtain. We advance that an inverse problem to obtain the mechanical properties of a given eye (e.g., Young's modulus, Poisson ratio) measuring its normal frequencies is doable. These measurements can be done using non-invasive techniques, opening very interesting perspectives to estimate the mechanical properties of eyes in vivo. Future research might relate various ocular pathologies with anomalies in measured vibrational frequencies of the eye.

physics.med-ph↗

arXiv2016

Termination of the MRI via parasitic instabilities in core-collapse supernovae: influence of numerical methods

We study the influence of numerical methods and grid resolution on the termination of the magnetorotational instability (MRI) by means of parasitic instabilities in three-dimensional shearing-disc simulations reproducing typical conditions found in core-collapse supernovae. Whether or not the MRI is able to amplify weak magnetic fields in this context strongly depends, among other factors, on the amplitude at which its growth terminates. The qualitative results of our study do not depend on the numerical scheme. In all our models, MRI termination is caused by Kelvin-Helmholtz instabilities, consistent with theoretical predictions. Quantitatively, however, there are differences, but numerical convergence can be achieved even at relatively low grid resolutions if high-order reconstruction methods are used.

astro-ph.SR↗

arXiv2014

A method for computing synchrotron and inverse-Compton emission from hydrodynamic simulations of supernova remnants

The observational signature of supernova remnants (SNRs) is very complex, in terms of both their geometrical shape and their spectral properties, dominated by non-thermal synchrotron and inverse-Compton scattering. We propose a post-processing method to analyse the broad-band emission of SNRs based on three-dimensional hydrodynamical simulations. From the hydrodynamical data, we estimate the distribution of non-thermal electrons accelerated at the shock wave and follow the subsequent evolution as they lose or gain energy by adiabatic expansion or compression and emit energy by radiation. As a first test case, we use a simulation of a bipolar supernova expanding into a cloudy medium. We find that our method qualitatively reproduces the main observational features of typical SNRs and produces fluxes that agree with observations to within a factor of a few. allowing for further use in more extended sets of models.

astro-ph.SR↗

arXiv2014

Hydrodynamic simulations of the interaction of supernova shock waves with a clumpy environment: the case of the RX J0852.0-4622 (Vela Jr) supernova remnant

Observations in all electromagnetic bands show that many supernova remnants (SNRs) have a very aspherical shape. This can be the result of asymmetries in the supernova explosion or a clumpy circumstellar medium. We study the generation of inhomogeneities and the mixing of elements arising from these two sources in multidimensional hydrodynamic simulations of the propagation of a supernova blast wave into a cloudy environment. We model a specific SNR, Vela Jr (RX J0852.0-4622). By comparing our results with recent observations, we can constrain the properties of the explosion. We find that a very energetic explosion of several 10^{51} erg occurring roughly about 800 years ago is consistent with the shape and emission of the SNR, as well as a supernova with an energy closer to the canonical value of 10^{51} erg a few thousand years ago.

astro-ph.SR↗

arXiv2010

Local simulations of the magnetized Kelvin-Helmholtz instability in neutron-star mergers

Context. Global MHD simulations show Kelvin-Helmholtz (KH) instabilities at the contact surface of two merging neutron stars. That region has been identified as the site of efficient amplification of magnetic fields. However, these global simulations, due to numerical limitations, were unable to determine the saturation level of the field strength, and thus the possible back-reaction of the magnetic field onto the flow. Aims. We investigate the amplification of initially weak fields in KH unstable shear flows, and the back-reaction of the field onto the flow. Methods. We use a high-resolution ideal MHD code to perform 2D and 3D local simulations of shear flows. Results. In 2D, the magnetic field is amplified in less than 0.01ms until it reaches locally equipartition with the kinetic energy. Subsequently, it saturates due to resistive instabilities that disrupt the KH vortex and decelerate the shear flow on a secular time scale. We determine scaling laws of the field amplification with the initial field strength and the grid resolution. In 3D, this hydromagnetic mechanism may be dominated by purely hydrodynamic instabilities limiting the amplification. We find maximum magnetic fields of 10^16 G locally, and r.m.s. maxima within the box of 10^15 G. However, such strong fields exist only for a short period. In the saturated state, the magnetic field is mainly oriented parallel to the shear flow for strong initial fields, while weaker initial fields tend to lead to a more balanced distribution of the field energy. In all models the flow shows small-scale features. The magnetic field is at most in equipartition with the decaying shear flow. (abridged)

astro-ph.SR↗

arXiv2009

Simulations of the Magneto-rotational Instability in Core-Collapse Supernovae

We assess the importance of the magneto-rotational instability in core-collapse supernovae by an analysis of the growth rates of unstable modes in typical post-collapse systems and by numerical simulations of simplified models. The interplay of differential rotation and thermal stratification defines different instability regimes which we confirm in our simulations. We investigate the termination of the growth of the MRI by parasitic instabilities, establish scaling laws characterising the termination amplitude, and study the long-term evolution of the saturated turbulent state.

astro-ph.SR↗