scholarly journals On the Bottom Magnetic Fields of Millisecond Pulsars

2004 ◽  
Vol 218 ◽  
pp. 47-48
Author(s):  
Chengmin Zhang
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Accretion Rate ◽  
Induced Magnetic Field ◽  
Radio Observations ◽  
Millisecond Pulsars ◽  
Low Field ◽  
Field Evolution ◽  
Field Decay ◽  
The Magnetic Field

The magnetic field strengths of most millisecond pulsars (MSPs) are about 108–9 gauss. The accretion-induced magnetic field evolution scenario here concludes that field decay is related to the accreted mass, that the minimum or bottom field stops at about 108 gauss for Eddington-limited accretion, and scales with the accretion rate as M1/2. The possibility of low field (∼ 107 gauss) MSPs has been proposed for future radio observations.

scholarly journals Decaying turbulence and magnetic fields in galaxy clusters

2019 ◽  
Vol 488 (3) ◽  
pp. 3439-3445 ◽  
Author(s):  
Sharanya Sur
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Galaxy Clusters ◽  
Power Law ◽  
Dynamo Action ◽  
Wide Range ◽  
Major Merger ◽  
Decaying Turbulence ◽  
Field Decay ◽  
The Magnetic Field

Abstract We explore the decay of turbulence and magnetic fields generated by fluctuation dynamo action in the context of galaxy clusters where such a decaying phase can occur in the aftermath of a major merger event. Using idealized numerical simulations that start from a kinetically dominated regime we focus on the decay of the steady state rms velocity and the magnetic field for a wide range of conditions that include varying the compressibility of the flow, the forcing wavenumber, and the magnetic Prandtl number. Irrespective of the compressibility of the flow, both the rms velocity and the rms magnetic field decay as a power law in time. In the subsonic case we find that the exponent of the power law is consistent with the −3/5 scaling reported in previous studies. However, in the transonic regime both the rms velocity and the magnetic field initially undergo rapid decay with an ≈t−1.1 scaling with time. This is followed by a phase of slow decay where the decay of the rms velocity exhibits an ≈−3/5 scaling in time, while the rms magnetic field scales as ≈−5/7. Furthermore, analysis of the Faraday rotation measure (RM) reveals that the Faraday RM also decays as a power law in time ≈t−5/7; steeper than the ∼t−2/5 scaling obtained in previous simulations of magnetic field decay in subsonic turbulence. Apart from galaxy clusters, our work can have potential implications in the study of magnetic fields in elliptical galaxies.

scholarly journals On the magnetic field of OH 231.8+4.2

2011 ◽  
Vol 7 (S283) ◽  
pp. 418-419
Author(s):  
Marcelo L. Leal-Ferreira ◽  
Wouter H. T. Vlemmings ◽  
Philip J. Diamond ◽  
Athol Kemball ◽  
Nikta Amiri ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Spherical Symmetry ◽  
Planetary Nebula ◽  
Initial Mass ◽  
Induced Magnetic Field ◽  
Tidal Forces ◽  
Star Binary ◽  
The Magnetic Field

AbstractDuring the transition from an AGB star to a planetary nebula, a large number of low/intermediate initial mass stars loses its spherical symmetry. The process responsible for that change of morphology is, so far, not well understood. The candidates responsible for shaping these objects are (i) a companion to the star (binary/heavy planet) and its tidal forces, (ii) disk interaction and (iii) magnetic fields - or a combination of these. In particular a binary induced magnetic field is a promising option. To study this we observed the polarization of H2O masers in the known binary pre-Planetary Nebula (pPN) OH231.8+4.2. Our results show a magnetic field B|| of ~45 mG is present in the H2O maser region of this pPN.

scholarly journals Magnetic Field Evolution in Neutron Star Crusts: Beyond the Hall Effect

Symmetry ◽  
2022 ◽  
Vol 14 (1) ◽  
pp. 130
Author(s):  
Konstantinos N. Gourgouliatos ◽  
Davide De Grandis ◽  
Andrei Igoshev
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Hall Effect ◽  
Thermal Emission ◽  
Ohmic Dissipation ◽  
Field Evolution ◽  
The Universe ◽  
The Magnetic Field ◽  
Maxwell Stresses

Neutron stars host the strongest magnetic fields that we know of in the Universe. Their magnetic fields are the main means of generating their radiation, either magnetospheric or through the crust. Moreover, the evolution of the magnetic field has been intimately related to explosive events of magnetars, which host strong magnetic fields, and their persistent thermal emission. The evolution of the magnetic field in the crusts of neutron stars has been described within the framework of the Hall effect and Ohmic dissipation. Yet, this description is limited by the fact that the Maxwell stresses exerted on the crusts of strongly magnetised neutron stars may lead to failure and temperature variations. In the former case, a failed crust does not completely fulfil the necessary conditions for the Hall effect. In the latter, the variations of temperature are strongly related to the magnetic field evolution. Finally, sharp gradients of the star’s temperature may activate battery terms and alter the magnetic field structure, especially in weakly magnetised neutron stars. In this review, we discuss the recent progress made on these effects. We argue that these phenomena are likely to provide novel insight into our understanding of neutron stars and their observable properties.

scholarly journals Magnetic Field Decay, or Just Period-Dependent Beaming?

2004 ◽  
Vol 218 ◽  
pp. 41-44 ◽  
Author(s):  
Joeri van Leeuwen ◽  
Frank Verbunt
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Velocity Distribution ◽  
Neutron Stars ◽  
Time Scale ◽  
Radio Pulsar ◽  
New Born ◽  
Field Decay ◽  
The Magnetic Field

Several recent papers conclude that radio-pulsar magnetic fields decay on a time-scale of 10 Myr, apparently contradicting earlier results. We have implemented the methods of these papers in our code and show that this preference for rapid field decay is caused by the assumption that the beaming fraction does not depend on the period. When we do include this dependence, we find that the observed pulsar properties are reproduced best when the modeled field does not decay. When we assume that magnetic fields of new-born neutron stars are from a distribution sufficiently wide to explain magnetars, the magnetic field and period distributions we predict for radio are pulsars wider than observed. Finally we find that the observed velocities overestimate the intrinsic velocity distribution.

scholarly journals On the weak magnetic field of millisecond pulsars: does it decay before accretion?

2019 ◽  
Vol 490 (2) ◽  
pp. 2013-2022 ◽  
Author(s):  
Marilyn Cruces ◽  
Andreas Reisenegger ◽  
Thomas M Tauris
Keyword(s):  
Magnetic Field ◽  
White Dwarf ◽  
Binary Systems ◽  
Alternative Hypothesis ◽  
General Distribution ◽  
Ohmic Dissipation ◽  
Millisecond Pulsars ◽  
Standard Scenario ◽  
Field Decay ◽  
The Magnetic Field

ABSTRACT Millisecond pulsars (MSPs) are old, fast spinning neutron stars (NSs) thought to have evolved from classical pulsars in binary systems, where the rapid rotation is caused by the accretion of matter and angular momentum from their companion. During this transition between classical and MSPs, there is a magnetic field reduction of ∼4 orders of magnitude, which is not well understood. According to the standard scenario, the magnetic field is reduced as a consequence of accretion, either through ohmic dissipation or through screening by the accreted matter. We explored an alternative hypothesis in which the magnetic field is reduced through ambipolar diffusion before the accretion. This is particularly effective during the long epoch in which the pulsar has cooled, but has not yet started accreting. This makes the final magnetic field dependent on the evolution time of the companion star and thus its initial mass. We use observed binary systems to constrain the time available for the magnetic field decay based on the current pulsar companion: a helium white dwarf, a carbon–oxygen white dwarf, or another NS. Based on a simplified model without baryon pairing, we show that the proposed process agrees with the general distribution of observed magnetic field strengths in binaries, but is not able to explain some mildly recycled pulsars where no significant decay appears to have occurred. We discuss the possibility of other formation channels for these systems and the conditions under which the magnetic field evolution would be set by the NS crust rather than the core.

scholarly journals Minimum accretion rate for millisecond pulsar formation in binary system

2012 ◽  
Vol 8 (S290) ◽  
pp. 291-292
Author(s):  
Yuanyue Pan ◽  
Chengmin Zhang ◽  
Na Wang
Keyword(s):  
Magnetic Field ◽  
Binary System ◽  
Accretion Rate ◽  
Millisecond Pulsar ◽  
Millisecond Pulsars ◽  
Spin Period ◽  
Binary Pulsars ◽  
Field Versus ◽  
The Magnetic Field

Abstract186 binary pulsars are shown in the magnetic field versus spin period (B-P) diagram, and their relations to the millisecond pulsars can be clearly seen. We declaim a minimum accretion rate for the millisecond pulsar formation both from the observation and theory. If the accretion rate is lower than the minimum accretion rate, the pulsar in binary system will not become a millisecond pulsar after the evolution.

scholarly journals Magnetic field evolution in magnetars

2012 ◽  
Vol 8 (S291) ◽  
pp. 425-427
Author(s):  
Yasufumi Kojima
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Neutron Stars ◽  
Dipole Field ◽  
Polar Field ◽  
Nonlinear Coupling ◽  
Strong Magnetic Fields ◽  
Field Decay ◽  
The Magnetic Field

AbstractDynamics of magnetic field decay is numerically studied. For neutron stars with strong magnetic fields, the Hall drift timescale in their crust is very short, and therefore the evolution is significantly affected. The nonlinear coupling between poloidal and toroidal components of the magnetic field is studied. It is also found that the polar field at the surface is highly distorted during the Hall drift timescale. For example, polar dipole field-strength temporarily decreases not by dissipation but by advection. This fact suggests that the dipole field-strength is not sufficient to determine the border between pulsars and magnetars.

LOW-FIELD INHOMOGENEITY-INDUCED MAGNETORESISTANCE IN SILICON

SPIN ◽  
2012 ◽  
Vol 02 (01) ◽  
pp. 1250002 ◽  
Author(s):  
XIAOZHONG ZHANG ◽  
CAIHUA WAN
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Giant Magnetoresistance ◽  
High Sensitivity ◽  
Boundary Region ◽  
Charge Carriers ◽  
Silicon Devices ◽  
Low Field ◽  
Silicon Based ◽  
The Magnetic Field

We show that inhomogeneity-induced magnetoresistance (IMR) in lightly doped silicon can be significantly enhanced through the injection of minority charge carriers, and then tuned by an applied current to have an onset at low magnetic fields. We designed an IMR device in which, the inhomogeneity is provided by the p–n boundary formed between regions where conduction is dominated by the minority and majority charge carriers respectively; application of a magnetic field distorts the current in the boundary region, resulting in large magnetoresistance. The room-temperature field sensitivity of our IMR device at low fields was remarkably improved, with magnetoresistance reaching 10% at 0.07 T and 100% at 0.2 T, approaching the performance of commercial giant magnetoresistance devices. The combination of high sensitivity to low magnetic fields and large high-field response should make this device concept attractive to the magnetic field sensing industry. Moreover, being based on a conventional silicon platform, it should be possible to integrate with existing silicon devices and so aid the development of silicon-based magnetoelectronics.

scholarly journals MHD Modeling of Solar Coronal Magnetic Evolution Driven by Photospheric Flow

2021 ◽  
Vol 9 ◽  
Author(s):  
Chaowei Jiang ◽  
Xinkai Bian ◽  
Tingting Sun ◽  
Xueshang Feng
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Energy ◽  
Data Driven ◽  
Surface Flows ◽  
Bottom Boundary ◽  
Field Evolution ◽  
Mhd Equilibrium ◽  
Field Lines ◽  
The Magnetic Field

It is well-known that magnetic fields dominate the dynamics in the solar corona, and new generation of numerical modeling of the evolution of coronal magnetic fields, as featured with boundary conditions driven directly by observation data, are being developed. This paper describes a new approach of data-driven magnetohydrodynamic (MHD) simulation of solar active region (AR) magnetic field evolution, which is for the first time that a data-driven full-MHD model utilizes directly the photospheric velocity field from DAVE4VM. We constructed a well-established MHD equilibrium based on a single vector magnetogram by employing an MHD-relaxation approach with sufficiently small kinetic viscosity, and used this MHD equilibrium as the initial conditions for subsequent data-driven evolution. Then we derived the photospheric surface flows from a time series of observed magentograms based on the DAVE4VM method. The surface flows are finally inputted in time sequence to the bottom boundary of the MHD model to self-consistently update the magnetic field at every time step by solving directly the magnetic induction equation at the bottom boundary. We applied this data-driven model to study the magnetic field evolution of AR 12158 with SDO/HMI vector magnetograms. Our model reproduced a quasi-static stress of the field lines through mainly the rotational flow of the AR's leading sunspot, which makes the core field lines to form a coherent S shape consistent with the sigmoid structure as seen in the SDO/AIA images. The total magnetic energy obtained in the simulation matches closely the accumulated magnetic energy as calculated directly from the original vector magnetogram with the DAVE4VM derived flow field. Such a data-driven model will be used to study how the coronal field, as driven by the slow photospheric motions, reaches a unstable state and runs into eruptions.

scholarly journals Pulsar Period and Magnetic Field Evolution

1996 ◽  
Vol 160 ◽  
pp. 39-46
Author(s):  
F. Camilo
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Fraction ◽  
Millisecond Pulsars ◽  
Pulsar Period ◽  
Field Evolution ◽  
Period Derivative ◽  
Formation And Evolution ◽  
Luminosity Evolution ◽  
P Distribution

AbstractOne of the important unsolved problems in pulsar astrophysics concerns the formation and evolution of their magnetic fields. We summarize measurements of braking indices and their implications for the spin and magnetic field evolution of young pulsars. An analysis of the period-period derivative diagram suggests one or more of the following: (a) a substantial population of young pulsars remains undiscovered; (b) a large fraction of all slow pulsars may be recycled; (c) magnetic fields in isolated pulsars decay by a factor of a few in the first few million years. We also note that the observed P-Ṗ distribution of millisecond pulsars may be shaped by luminosity evolution.

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