scholarly journals Magnetorotational core collapse of possible GRB progenitors – II. Formation of protomagnetars and collapsars

2020 ◽  
Vol 500 (4) ◽  
pp. 4365-4397
Author(s):  
M Á Aloy ◽  
M Obergaulinger
Keyword(s):  
Magnetic Field ◽  
Gamma Ray ◽  
Core Collapse ◽  
Poloidal Magnetic Field ◽  
Episodic Events ◽  
Long Time ◽  
Low Metallicity ◽  
Dipolar Fields ◽  
Poloidal Magnetic Fields ◽  
Protoneutron Star

ABSTRACT We assess the variance of the post-collapse evolution remnants of compact, massive, low-metallicity stars, under small changes in the degrees of rotation and magnetic field of selected pre-supernova cores. These stellar models are commonly considered progenitors of long gamma-ray bursts. The fate of the protoneutron star (PNS) formed after the collapse, whose mass may continuously grow due to accretion, critically depends on the poloidal magnetic field strength at bounce. Should the poloidal magnetic field be sufficiently weak, the PNS collapses to a black hole (BH) within a few seconds. Models on this evolutionary track contain promising collapsar engines. Poloidal magnetic fields smooth over large radial scales (e.g. dipolar fields) or slightly augmented with respect to the original pre-supernova core yield long-lasting PNSs. In these models, BH formation is avoided or staved off for a long time, hence, they may produce protomagnetars (PMs). Some of our PM candidates have been run for $\lesssim 10\,$ s after core bounce, but they have not entered the Kelvin–Helmholtz phase yet. Among these models, some display episodic events of spin-down during which we find properties broadly compatible with the theoretical expectations for PMs ($M_\rm {\small PNS}\approx 1.85{-}2.5\, \mathrm{M}_{\odot }$, $\bar{P}_\rm {\small PNS}\approx 1.5 {-} 4\,$ ms, and $b^{\rm surf}_\rm {\small PNS}\lesssim 10^{15}\,$ G) and their very collimated supernova ejecta have nearly reached the stellar surface with (still growing) explosion energies $\gtrsim {2} \times 10^{51}\, \textrm {erg}$.

scholarly journals SNR G39.2−0.3, an hadronic cosmic rays accelerator

2020 ◽  
Vol 497 (3) ◽  
pp. 3581-3590
Author(s):  
Emma de Oña Wilhelmi ◽  
Iurii Sushch ◽  
Robert Brose ◽  
Enrique Mestre ◽  
Yang Su ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Galactic Cosmic Rays ◽  
Spectral Energy ◽  
Core Collapse ◽  
Heavy Nuclei ◽  
The Rich

ABSTRACT Recent results obtained with gamma-ray satellites have established supernova remnants as accelerators of GeV hadronic cosmic rays. In such processes, CRs accelerated in SNR shocks interact with particles from gas clouds in their surrounding. In particular, the rich medium in which core-collapse SNRs explode provides a large target density to boost hadronic gamma-rays. SNR G39.2–0.3 is one of the brightest SNR in infrared wavelengths, and its broad multiwavelength coverage allows a detailed modelling of its radiation from radio to high energies. We reanalysed the Fermi-LAT data on this region and compare it with new radio observations from the MWISP survey. The modelling of the spectral energy distribution from radio to GeV energies favours a hadronic origin of the gamma-ray emission and constrains the SNR magnetic field to be at least ∼100 µG. Despite the large magnetic field, the present acceleration of protons seems to be limited to ∼10 GeV, which points to a drastic slow down of the shock velocity due to the dense wall traced by the CO observations, surrounding the remnant. Further investigation of the gamma-ray spectral shape points to a dynamically old remnant subjected to severe escape of CRs and a decrease of acceleration efficiency. The low-energy peak of the gamma-ray spectrum also suggests that that the composition of accelerated particles might be enriched by heavy nuclei which is certainly expected for a core-collapse SNR. Alternatively, the contribution of the compressed pre-existing Galactic cosmic rays is discussed, which is, however, found to not likely be the dominant process for gamma-ray production.

scholarly journals How to form a millisecond magnetar? Magnetic field amplification in protoneutron stars

2017 ◽  
Vol 12 (S331) ◽  
pp. 119-124 ◽  
Author(s):  
Jérôme Guilet ◽  
Ewald Müller ◽  
Hans-Thomas Janka ◽  
Tomasz Rembiasz ◽  
Martin Obergaulinger ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Gamma Ray ◽  
Core Collapse ◽  
Magnetorotational Instability ◽  
Strong Magnetic Fields ◽  
Physical Conditions ◽  
Field Amplification ◽  
Magnetic Prandtl Number ◽  
Protoneutron Stars

AbstractExtremely strong magnetic fields of the order of 1015G are required to explain the properties of magnetars, the most magnetic neutron stars. Such a strong magnetic field is expected to play an important role for the dynamics of core-collapse supernovae, and in the presence of rapid rotation may power superluminous supernovae and hypernovae associated to long gamma-ray bursts. The origin of these strong magnetic fields remains, however, obscure and most likely requires an amplification over many orders of magnitude in the protoneutron star. One of the most promising agents is the magnetorotational instability (MRI), which can in principle amplify exponentially fast a weak initial magnetic field to a dynamically relevant strength. We describe our current understanding of the MRI in protoneutron stars and show recent results on its dependence on physical conditions specific to protoneutron stars such as neutrino radiation, strong buoyancy effects and large magnetic Prandtl number.

scholarly journals Deformation of neutron stars due to poloidal magnetic fields

2019 ◽  
Vol 2019 (8) ◽  
Author(s):  
K Yanase ◽  
N Yoshinaga ◽  
E Nakano ◽  
C Watanabe
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Strong Magnetic Field ◽  
Axially Symmetric ◽  
Poloidal Magnetic Field ◽  
The One ◽  
Poloidal Magnetic Fields

Abstract The mass–radius (MR) relation of deformed neutron stars in the axially symmetric poloidal magnetic field is calculated. The MR relation is obtained by solving the Hartle equations, whereas the one for spherical stars is obtained by the Tolman–Oppenheimer–Volkoff equations. The anisotropic effects of the poloidal magnetic fields are found to be non-negligible for a strong magnetic field more than $3\times10^{18}$ G at the center of a neutron star.

scholarly journals OUTFLOWS FROM MAGNETOROTATIONAL SUPERNOVAE

2008 ◽  
Vol 17 (09) ◽  
pp. 1411-1417 ◽  
Author(s):  
S. G. MOISEENKO ◽  
G. S. BISNOVATYI-KOGAN
Keyword(s):  
Magnetic Field ◽  
Shock Wave ◽  
Supernova Explosion ◽  
Core Collapse ◽  
Rotational Axis ◽  
Magnetorotational Instability ◽  
Poloidal Magnetic Field ◽  
Core Mass ◽  
Supernova Explosions ◽  
Initial Magnetic Field

We discuss results of 2D simulations of magnetorotational (MR) mechanism of core collapse supernova explosions. Due to the nonuniform collapse, the collapsed core rotates differentially. In the presence of an initial poloidal magnetic field its toroidal component appears and grows with time. Increased magnetic pressure leads to the formation of a compression wave which moves outwards. It transforms into the fast MHD shock wave (supernova shock wave). The shape of the MR supernova explosion qualitatively depends on the configuration of the initial magnetic field. For a dipole-like initial magnetic field, the supernova explosion develops mainly along the rotational axis, forming a mildly collimated jet. A quadrupole-like initial magnetic field leads to the explosion developing mainly along the equatorial plane. The magnetorotational instability was found in our simulations. The supernova explosion energy grows with an increase of the initial core mass and rotational energy of the core, and corresponds to the observational data.

scholarly journals Limiting magnetic field for minimal deformation of a magnetized neutron star

2019 ◽  
Vol 627 ◽  
pp. A61 ◽  
Author(s):  
R. O. Gomes ◽  
H. Pais ◽  
V. Dexheimer ◽  
C. Providência ◽  
S. Schramm
Keyword(s):  
Magnetic Field ◽  
Neutron Stars ◽  
Magnetic Moment ◽  
Spherical Symmetry ◽  
Degrees Of Freedom ◽  
Gamma Ray ◽  
Mean Field ◽  
Field Equations ◽  
Poloidal Magnetic Field ◽  
The Magnetic Field

Aims. In this work, we study the structure of neutron stars under the effect of a poloidal magnetic field and determine the limiting largest magnetic field strength that induces a deformation such that the ratio between the polar and equatorial radii does not exceed 2%. We consider that, under these conditions, the description of magnetic neutron stars in the spherical symmetry regime is still satisfactory. Methods. We described different compositions of stars (nucleonic, hyperonic, and hybrid) using three state-of-the-art relativistic mean field models (NL3ωρ, MBF, and CMF, respectively) for the microscopic description of matter, all in agreement with standard experimental and observational data. The structure of stars was described by the general relativistic solution of both Einstein’s field equations assuming spherical symmetry and Einstein-Maxwell’s field equations assuming an axi-symmetric deformation. Results. We find a limiting magnetic moment on the order of 2 × 1031 Am2, which corresponds to magnetic fields on the order of 1016 G at the surface and 1017 G at the center of the star, above which the deformation due to the magnetic field is above 2%, and therefore not negligible. We show that the intensity of the magnetic field developed in the star depends on the equation of state (EoS), and, for a given baryonic mass and fixed magnetic moment, larger fields are attained with softer EoS. We also show that the appearance of exotic degrees of freedom, such as hyperons or a quark core, is disfavored in the presence of a very strong magnetic field. As a consequence, a highly magnetized nucleonic star may suffer an internal conversion due to the decay of the magnetic field, which could be accompanied by a sudden cooling of the star or a gamma ray burst.

scholarly journals UNSTABLE ELECTROMAGNETIC MODES IN STRONGLY MAGNETIZED PLASMAS

2013 ◽  
Vol 27 (30) ◽  
pp. 1350151
Author(s):  
S. SON ◽  
SUNG JOON MOON
Keyword(s):  
Magnetic Field ◽  
Strong Magnetic Field ◽  
Inertial Confinement Fusion ◽  
Gamma Ray ◽  
Landau Damping ◽  
Magnetized Plasmas ◽  
Inertial Confinement ◽  
Electron Motion ◽  
Confinement Fusion ◽  
Long Time

A theory for instability in the long-time limit, arising from the electron gyro-motion in strongly magnetized plasmas, is presented. The analysis of the electron motion in the presence of a strong magnetic field leads to a theoretical framework similar to that of the Landau damping. Various electromagnetic modes are predicted to be possibly unstable, and the regime where the radiation from this instability would stand out, compared to the incoherent electron–cyclotron radiation, is identified. This instability would be relevant to the inertial confinement fusion and the gamma ray burst.

scholarly journals Magnetic nulls in interacting dipolar fields

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
Todd Elder ◽  
Allen H. Boozer
Keyword(s):  
Magnetic Field ◽  
Current Density ◽  
Magnetic Flux Tube ◽  
Electron Inertia ◽  
Characteristic Spatial Scale ◽  
Field Lines ◽  
Dipolar Fields ◽  
Time Required ◽  
Magnetic Null ◽  
The Magnetic Field

The prominence of nulls in reconnection theory is due to the expected singular current density and the indeterminacy of field lines at a magnetic null. Electron inertia changes the implications of both features. Magnetic field lines are distinguishable only when their distance of closest approach exceeds a distance $\varDelta _d$ . Electron inertia ensures $\varDelta _d\gtrsim c/\omega _{pe}$ . The lines that lie within a magnetic flux tube of radius $\varDelta _d$ at the place where the field strength $B$ is strongest are fundamentally indistinguishable. If the tube, somewhere along its length, encloses a point where $B=0$ vanishes, then distinguishable lines come no closer to the null than $\approx (a^2c/\omega _{pe})^{1/3}$ , where $a$ is a characteristic spatial scale of the magnetic field. The behaviour of the magnetic field lines in the presence of nulls is studied for a dipole embedded in a spatially constant magnetic field. In addition to the implications of distinguishability, a constraint on the current density at a null is obtained, and the time required for thin current sheets to arise is derived.

scholarly journals On the dynamical interaction between overshooting convection and an underlying dipole magnetic field – I. The non-dynamo regime

2021 ◽  
Vol 503 (1) ◽  
pp. 362-375
Author(s):  
L Korre ◽  
NH Brummell ◽  
P Garaud ◽  
C Guervilly
Keyword(s):  
Magnetic Field ◽  
Turbulent Diffusion ◽  
Large Scale ◽  
Molecular Diffusion ◽  
Mean Field ◽  
Stable Region ◽  
Turbulent Regime ◽  
Poloidal Magnetic Field ◽  
Dynamical Interaction ◽  
Large Scale Field

ABSTRACT Motivated by the dynamics in the deep interiors of many stars, we study the interaction between overshooting convection and the large-scale poloidal fields residing in radiative zones. We have run a suite of 3D Boussinesq numerical calculations in a spherical shell that consists of a convection zone with an underlying stable region that initially compactly contains a dipole field. By varying the strength of the convective driving, we find that, in the less turbulent regime, convection acts as turbulent diffusion that removes the field faster than solely molecular diffusion would do. However, in the more turbulent regime, turbulent pumping becomes more efficient and partially counteracts turbulent diffusion, leading to a local accumulation of the field below the overshoot region. These simulations suggest that dipole fields might be confined in underlying stable regions by highly turbulent convective motions at stellar parameters. The confinement is of large-scale field in an average sense and we show that it is reasonably modelled by mean-field ideas. Our findings are particularly interesting for certain models of the Sun, which require a large-scale, poloidal magnetic field to be confined in the solar radiative zone in order to explain simultaneously the uniform rotation of the latter and the thinness of the solar tachocline.

scholarly journals Broadband Linear Polarization in Ap Stars

1993 ◽  
Vol 138 ◽  
pp. 305-309
Author(s):  
Marco Landolfi ◽  
Egidio Landi Degl’Innocenti ◽  
Maurizio Landi Degl’Innocenti ◽  
Jean-Louis Leroy ◽  
Stefano Bagnulo
Keyword(s):  
Magnetic Field ◽  
Circular Polarization ◽  
Linear Polarization ◽  
Rotation Axis ◽  
Spectral Lines ◽  
Line Of Sight ◽  
Long Time ◽  
Rotating Star ◽  
Ap Stars ◽  
The Magnetic Field

AbstractBroadband linear polarization in the spectra of Ap stars is believed to be due to differential saturation between σ and π Zeeman components in spectral lines. This mechanism has been known for a long time to be the main agent of a similar phenomenon observed in sunspots. Since this phenomenon has been carefully calibrated in the solar case, it can be confidently used to deduce the magnetic field of Ap stars.Given the magnetic configuration of a rotating star, it is possible to deduce the broadband polarization at any phase. Calculations performed for the oblique dipole model show that the resulting polarization diagrams are very sensitive to the values of i (the angle between the rotation axis and the line of sight) and β (the angle between the rotation and magnetic axes). The dependence on i and β is such that the four-fold ambiguity typical of the circular polarization observations ((i,β), (β,i), (π-i,π-β), (π-β,π-i)) can be removed.

scholarly journals Constraining the coherence scale of the interstellar magnetic field using TeV gamma-ray observations of supernova remnants

2020 ◽  
Vol 496 (2) ◽  
pp. 2448-2461 ◽  
Author(s):  
Matteo Pais ◽  
Christoph Pfrommer ◽  
Kristian Ehlert ◽  
Maria Werhahn ◽  
Georg Winner
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Galactic Cosmic Rays ◽  
Shock Acceleration ◽  
Interstellar Gas ◽  
Narrow Angle ◽  
Magnetohydrodynamic Simulations ◽  
Tev Gamma Rays

ABSTRACT Galactic cosmic rays (CRs) are believed to be accelerated at supernova remnant (SNR) shocks. In the hadronic scenario, the TeV gamma-ray emission from SNRs originates from decaying pions that are produced in collisions of the interstellar gas and CRs. Using CR-magnetohydrodynamic simulations, we show that magnetic obliquity-dependent shock acceleration is able to reproduce the observed TeV gamma-ray morphology of SNRs such as Vela Jr and SN1006 solely by varying the magnetic morphology. This implies that gamma-ray bright regions result from quasi-parallel shocks (i.e. when the shock propagates at a narrow angle to the upstream magnetic field), which are known to efficiently accelerate CR protons, and that gamma-ray dark regions point to quasi-perpendicular shock configurations. Comparison of the simulated gamma-ray morphology to observations allows us to constrain the magnetic coherence scale λB around Vela Jr and SN1006 to $\lambda _B \simeq 13_{-4.3}^{+13}$ pc and $\lambda _B \gt 200_{-40}^{+50}$ pc, respectively, where the ambient magnetic field of SN1006 is consistent with being largely homogeneous. We find consistent pure hadronic and mixed hadronic-leptonic models that both reproduce the multifrequency spectra from the radio to TeV gamma-rays and match the observed gamma-ray morphology. Finally, to capture the propagation of an SNR shock in a clumpy interstellar medium, we study the interaction of a shock with a dense cloud with numerical simulations and analytics. We construct an analytical gamma-ray model for a core collapse SNR propagating through a structured interstellar medium, and show that the gamma-ray luminosity is only biased by 30 per cent for realistic parameters.

Sign in / Sign up

Export Citation Format

Share Document