Browsing by Author "Reisenegger, Andreas"

Now showing 1 - 20 of 64
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    A redshift database towards the Shapley supercluster region
    (2020) Quintana Godoy, Hernán; Proust, D.; Dünner Planella, Rolando; Carrasco, E. R.; Reisenegger, Andreas
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    Asymptotic, non-linear solutions for ambipolar diffusion in one dimension
    (2010) Hoyos Barrios, Jaime; Reisenegger, Andreas
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    B fields in OB stars (BOB) : on the detection of weak magnetic fields in the two early B-type stars beta CMa and epsilon CMa Possible lack of a "magnetic desert" in massive stars
    (2015) Fossati, L.; Castro, N.; Morel, T.; Langer, N.; Briquet, M.; Carroll, T. A.; Hubrig, S.; Nieva, M. F.; Oskinova, L. M.; Reisenegger, Andreas
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    B fields in OB stars (BOB) Detection of a strong magnetic field in the O9.7 V star HD 54879
    (2015) Castro, N.; Fossati, L.; Hubrig, S.; Simon-Diaz, S.; Schöller, M.; Ilyin, I.; Carrol, T. A.; Langer, N.; Morel, T.; Reisenegger, Andreas
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    Constraining the equation of state of dense nuclear matter using thermal emission of neutron stars
    (2020) Baillot d’Étivaux, Nicolas; Margueron, Jérôme; Guillot, Sebastien; Webb, Natalie; Catelan, Márcio; Reisenegger, Andreas
    In this work, the equation of state (EoS) of the dense matter in the core of neutron stars (NSs) is based on a recently proposed meta-modeling of nuclear matter composed of nucleons, which can be parametrized by empirical quantities such as the energy density at saturation density or the nuclear incompressibility modulus. We use a set of recent observations of the thermal emission of seven NSs in quiescent low-mass X-ray binaries (qLMXBs) in order to find some constraints on the parameters of the meta-model, and thus on the nuclear EoS. This is done in a Bayesian statistical framework using Markov Chain Monte Carlo (MCMC) methods, to perform a simultaneous analysis over the seven sources. For the first time, the theoretical modeling of the EoS is directly implemented in the data analysis. We obtain constraints on the slope of the symmetry energy, {L}sym={37.2}-8.9+9.2 MeV, and give the first estimation of its curvature, {K}sym=-{85}-70+82 MeV, and on the isoscalar skewness parameter, {Q}sat={318}-366+673 MeV. Radii of about 12 km are preferred with a good fit statistic, yielding a nuclear EoS that is consistent with observational data and recent gravitational waves signals from NSs coalescence....
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    Contrasting neutron star heating mechanisms with Hubble Space Telescope observations
    (2018) Rodríguez Tapia, Luis; Reisenegger, Andreas; Pontificia Universidad Católica de Chile. Instituto de Física
    Si las estrellas de neutrones se enfriaran pasivamente, se esperaría que se vuelvan indetectables en un tiempo menor a 107 años, al alcanzar bajas temperaturas T < 104 K. Sin embargo, radiación del tipo ultravioleta, que implica temperaturas superficiales T ∼ 105 K, fue detectada desde los pulsares de Giga años PSR J0437- 4715 y PSR J2124-3358 y también desde el pulsar B0950+08 cuya edad es ∼ 107 años. Esta discrepancia puede ser explicada por un grupo de mecanismos de calentamiento propuestos en la literatura. Usando el código de Petrovich y Reisenegger se calcularon curvas de evolución térmica considerando diferentes mecanismos de calentamiento. Estas fueron contrastadas con las temperaturas inferidas a partir de las observaciones de los pulsares para determinar cuál es la principal fuente de emisión térmica de las estrellas de neutrones. Encontramos que el calentamiento rotoquímico, reacciones nucleares en las capas profundas de la corteza y el calor liberado por la fricción de vórtices superfluidos pueden mantener la estrella lo suficientemente caliente más allá del tiempo estándar de enfriamiento pasivo y explicar las observaciones.Si las estrellas de neutrones se enfriaran pasivamente, se esperaría que se vuelvan indetectables en un tiempo menor a 107 años, al alcanzar bajas temperaturas T < 104 K. Sin embargo, radiación del tipo ultravioleta, que implica temperaturas superficiales T ∼ 105 K, fue detectada desde los pulsares de Giga años PSR J0437- 4715 y PSR J2124-3358 y también desde el pulsar B0950+08 cuya edad es ∼ 107 años. Esta discrepancia puede ser explicada por un grupo de mecanismos de calentamiento propuestos en la literatura. Usando el código de Petrovich y Reisenegger se calcularon curvas de evolución térmica considerando diferentes mecanismos de calentamiento. Estas fueron contrastadas con las temperaturas inferidas a partir de las observaciones de los pulsares para determinar cuál es la principal fuente de emisión térmica de las estrellas de neutrones. Encontramos que el calentamiento rotoquímico, reacciones nucleares en las capas profundas de la corteza y el calor liberado por la fricción de vórtices superfluidos pueden mantener la estrella lo suficientemente caliente más allá del tiempo estándar de enfriamiento pasivo y explicar las observaciones.
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    Deep Optical Observations of the Fields of Two Nearby Millisecond Pulsars With the Vlt
    (2003) Sutaria, F.; Reisenegger, Andreas; Quintana Godoy, Hernán; Minniti, D.
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    Evolution of random initial magnetic fields in stably stratified and barotropic stars
    (2022) Becerra, Laura; Reisenegger, Andreas; Alejandro Valdivia, Juan; Gusakov, Mikhail E.
    Long-lived magnetic fields are known to exist in upper main-sequence stars, white dwarfs, and neutron stars. In order to explore possible equilibrium configurations of the magnetic field inside these stars, we have performed 3D magnetohydrodynamic simulations of the evolution of initially random magnetic fields in stably stratified and barotropic stars with an ideal-gas equation of state using the pencil code, a high-order finite-difference code for compressible hydrodynamic flows in the presence of magnetic fields. In barotropic (isentropic) stars, we confirm previous results in the sense that all initial magnetic fields we tried decay away, unable to reach a stable equilibrium. In the case of stably stratified stars (with radially increasing specific entropy), initially random magnetic fields appear to always evolve to a stable equilibrium. However, the nature of this equilibrium depends on the dissipation mechanisms considered. If magnetic diffusivity (or hyper-diffusivity) is included, the final state is more axially symmetric and dominated by large wavelengths than the initial state, whereas this is not the case if only viscosity (or hyper-viscosity) is present. In real stars, the main mechanism allowing them to relax to equilibrium is likely to be phase mixing, which we argue is more closely mimicked by viscosity. Therefore, we conclude that, depending on its formation mechanism, the equilibrium magnetic field in these stars could in principle be very asymmetric.
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    Fast Radio Bursts : constraining possible astrophysical scenarios from a particle acceleration model
    (2020) Zepeda González, Felipe; Reisenegger, Andreas; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
    Fast Radio Bursts (FRBs) are bright millisecond-long radio flashes that imply strong electromagnetic waves in their vicinity. We analyzed the acceleration experienced by particles under such intense fields, and we obtained that they will quickly become relativistic and move in the direction of the incident wave. In this process, the particles periodically reach a high Lorentz factor, which remains valid up to the radial distance r_f \sim 3 \times 10^{10} {\rm cm} \, (m/m_p)^{-1} L_{42}^{1/2} \nu_9^{-1}. We analyzed the possible formation of a charge separation region due to the different r_f of protons and electrons, and then we argued about the possible disruption of the electron acceleration process at r> r_f. We also analyzed the incoherent and coherent radiation processes experienced by the accelerating particles and concluded that the coherent radiation can substantially disperse the energy of the incident wave if the emission mechanism of the FRB is activated at r < r_{f,p^+}. Based on this, our model disfavours mechanisms in which the FRB is emitted from within the magnetosphere of a NS or magnetar as a progenitor scenario. Although the model was applied to FRBs, it is applicable to other FRB-like phenomena. We propose to extend our analysis by self-consistently solving the Maxwell equations and the equations of motion for the plasma.
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    Future evolution of bound superclusters in an accelerating Universe
    (2009) Araya-Melo, PA.; Reisenegger, Andreas; Dünner Planella, Rolando; Quintana Godoy, Hernán
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    Hall drift of axisymmetric magnetic fields in solid neutron-star matter
    (2007) Reisenegger, Andreas; Benguria Donoso, Rafael
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    Hubble Space Telescope Detection of the Millisecond Pulsar J2124-3358 and its Far-ultraviolet Bow Shock Nebula
    (2017) Reisenegger, Andreas; Rangelov, B.; Pavlov, G. G.; Kargaltsev, O.; Guillot, S.; Van Kerkwijk, M. H.
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    Hubble Space Telescope Nondetection of PSR J2144-3933 : The Coldest Known Neutron Star
    (2019) Guillot, S.; Pavlov, G.G.; Reyes, C.; Reisenegger, Andreas; Rodríguez Pemjean, Luis Enrique; Rangelov, B.; Kargaltsev, O.
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