scholarly journals Radiation-Driven Acceleration in Photospheres of Nonaccreting Magnetic White Dwarfs

1994 ◽  
Vol 142 ◽  
pp. 783-787
Author(s):  
Vladimir V. Zheleznyakov ◽  
A. V. Serber
Keyword(s):  
Magnetic Field ◽  
Radiation Pressure ◽  
White Dwarfs ◽  
Force Balance ◽  
Pure Hydrogen ◽  
Uv Spectrum ◽  
Dipole Magnetic Field ◽  
Cyclotron Line ◽  
The Magnetic Field ◽  
Radiation Pressure Force

AbstractRadiation transfer in a pure hydrogen, fully ionized, isothermal photosphere of an isolated white dwarf with dipole magnetic field is considered, and the radiation pressure force, both in the continuum and in the cyclotron line, is determined with the line saturation effect taken into account. It is shown that the magnetic field can reduce the critical luminosity for white dwarfs. This leads to the possibility of photospheric plasma ejection driven by the radiation in the cyclotron line and the formation of radiation-driven winds from sufficiently hot isolated magnetic white dwarfs.It is shown that cyclotron radiation pressure plays a significant role in the force balance of the photospheres of the magnetic white dwarfs GD 229, GrW +70° 8247, and PG 1031+234. The strong unidentified depression in the UV spectrum of GD 229 is attributed to cyclotron scattering by the radiation-driven plasma envelope with density N ≳ 108 cm−3 .Subject headings: radiative transfer — stars: atmospheres — stars: magnetic fields — white dwarfs

scholarly journals Evidence for the radiation-pressure dominated accretion disk in bursting pulsar GRO J1744−28 using timing analysis

2019 ◽  
Vol 626 ◽  
pp. A106 ◽  
Author(s):  
Juhani Mönkkönen ◽  
Sergey S. Tsygankov ◽  
Alexander A. Mushtukov ◽  
Victor Doroshenko ◽  
Valery F. Suleimanov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Accretion Disk ◽  
Radiation Pressure ◽  
Compact Objects ◽  
Disk Radius ◽  
Line Energy ◽  
X Ray ◽  
Inner Radius ◽  
Cyclotron Line ◽  
The Magnetic Field

The X-ray pulsar GRO J1744−28 is a unique source that shows both pulsations and type-II X-ray bursts, allowing studies of the interaction of the accretion disk with the magnetosphere at huge mass-accretion rates exceeding 1019 g s−1 during its super-Eddington outbursts. The magnetic field strength in the source, B ≈ 5 × 1011 G, is known from the cyclotron absorption feature discovered in the energy spectrum around 4.5 keV. Here, we have explored the flux variability of the source in context of interaction of its magnetosphere with the radiation-pressure dominated accretion disk. Specifically, we present the results of the analysis of noise power density spectra (PDS) using the observations of the source in 1996–1997 by the Rossi X-ray Timing Explorer (RXTE). Accreting compact objects commonly exhibit a broken power-law PDS shape with a break corresponding to the Keplerian orbital frequency of matter at the innermost disk radius. The observed frequency of the break can thus be used to estimate the size of the magnetosphere. We find, however, that the observed PDS of GRO J1744−28 differs dramatically from the canonical shape. The observed break frequency appears to be significantly higher than expected based on the magnetic field estimated from the cyclotron line energy. We argue that these observational facts can be attributed to the existence of the radiation-pressure dominated region in the accretion disk at luminosities above ∼2 × 1037 erg s−1. We discuss a qualitative model for the PDS formation in such disks, and show that its predictions are consistent with our observational findings. The presence of the radiation-pressure dominated region can also explain the observed weak luminosity dependence of the inner radius, and we argue that the small inner radius can be explained by a quadrupole component dominating the magnetic field of the neutron star.

scholarly journals Radio Emission Model of a 'Typical' Pulsar

1987 ◽  
Vol 40 (6) ◽  
pp. 755 ◽  
Author(s):  
AZ Kazbegi ◽  
GZ Machabeli ◽  
G Melikidze
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Waves ◽  
Emission Model ◽  
Radio Waves ◽  
Resonance Case ◽  
Pulsar Magnetosphere ◽  
Pulsar Emission ◽  
Dipole Magnetic Field ◽  
New Type ◽  
The Magnetic Field

The generation of radio waves in the plasma of the pulsar magnetosphere is considered taking into account the inhomogeneity of the dipole magnetic field. It is shown that the growth rate of the instability of the electromagnetic waves calculated in the non-resonance case turns out to be of the order of 1/ TO (where TO is the time of plasma escape from the light cylinder). However, the generation of electromagnetic waves from a new type Cherenkov resonance is possible, occurring when the particles have transverse velocities caused by the drift due to the inhomogeneity of the magnetic field. Estimates show that the development of this type of instability is possible only for pulsars with ages which exceed 104 yr. We make an attempt to explain some peculiarities of 'typical' pulsar emission on the basis of the model developed.

scholarly journals Cyclotron lines in highly magnetized neutron stars

2019 ◽  
Vol 622 ◽  
pp. A61 ◽  
Author(s):  
R. Staubert ◽  
J. Trümper ◽  
E. Kendziorra ◽  
D. Klochkov ◽  
K. Postnov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Direct Measurement ◽  
Resonant Scattering ◽  
Electron Cyclotron ◽  
X Ray ◽  
Cyclotron Line ◽  
The Magnetic Field ◽  
Proton Cyclotron

Cyclotron lines, also called cyclotron resonant scattering features are spectral features, generally appearing in absorption, in the X-ray spectra of objects containing highly magnetized neutron stars, allowing the direct measurement of the magnetic field strength in these objects. Cyclotron features are thought to be due to resonant scattering of photons by electrons in the strong magnetic fields. The main content of this contribution focusses on electron cyclotron lines as found in accreting X-ray binary pulsars (XRBP) with magnetic fields on the order of several 1012Gauss. Also, possible proton cyclotron lines from single neutron stars with even stronger magnetic fields are briefly discussed. With regard to electron cyclotron lines, we present an updated list of XRBPs that show evidence of such absorption lines. The first such line was discovered in a 1976 balloon observation of the accreting binary pulsar Hercules X-1, it is considered to be the first direct measurement of the magnetic field of a neutron star. As of today (end 2018), we list 35 XRBPs showing evidence of one ore more electron cyclotron absorption line(s). A few have been measured only once and must be confirmed (several more objects are listed as candidates). In addition to the Tables of objects, we summarize the evidence of variability of the cyclotron line as a function of various parameters (especially pulse phase, luminosity and time), and add a discussion of the different observed phenomena and associated attempts of theoretical modeling. We also discuss our understanding of the underlying physics of accretion onto highly magnetized neutron stars. For proton cyclotron lines, we present tables with seven neutron stars and discuss their nature and the physics in these objects.

scholarly journals Discovery of weak magnetic fields in four DZ white dwarfs in the local 20 pc volume

2019 ◽  
Vol 630 ◽  
pp. A65 ◽  
Author(s):  
S. Bagnulo ◽  
J. D. Landstreet
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
White Dwarfs ◽  
Field Measurements ◽  
Weak Magnetic Fields ◽  
Polluted Atmosphere ◽  
Highly Sensitive ◽  
Cool White Dwarfs ◽  
The Magnetic Field ◽  
Made In

We report the discovery of weak magnetic fields in three white dwarfs within the local 20 pc volume (WD 0816−310, WD 1009−184, and WD 1532+129), and we confirm the magnetic nature of a fourth star (WD 2138−332) in which we had previously detected a field at a 3σ level. The spectra of all these white dwarfs are characterised by the presence of metal lines and lack of H and He lines, that is, they belong to the spectral class DZ. The polarisation signal of the Ca II H+K lines of WD 1009−184 is particularly spectacular, with an amplitude of 20% that is due to the presence of a magnetic field with an average line-of-sight component of 40 kG. We have thus established that at least 40% of the known DZ white dwarfs with an He-rich atmosphere contained in the 20 pc volume have a magnetic field, while further observations are needed to establish whether the remaining DZ white dwarfs in the same volume are magnetic or not. Metal lines in the spectra of DZ white dwarfs are thought to have originated by accretion from rocky debris, and it might be argued that a link exists between metal accretion and higher occurrence of magnetism. However, we are not able to distinguish whether the magnetic field and the presence of a polluted atmosphere have a common origin, or if it is the presence of metal lines that allows us to detect a higher frequency of magnetic fields in cool white dwarfs, which would otherwise have featureless spectra. We argue that the new highly sensitive longitudinal field measurements that we have made in recent years are consistent with the idea that the magnetic field appears more frequently in older than in younger white dwarfs.

scholarly journals Revisiting some physics issues related to the new mass limit for magnetized white dwarfs

2014 ◽  
Vol 29 (07) ◽  
pp. 1450035 ◽  
Author(s):  
Upasana Das ◽  
Banibrata Mukhopadhyay
Keyword(s):  
Magnetic Field ◽  
High Magnetic Field ◽  
White Dwarfs ◽  
Total Density ◽  
Mass Limit ◽  
The Magnetic Field

We clarify important physics issues related to the recently established new mass limit for magnetized white dwarfs which is significantly super-Chandrasekhar. The issues include, justification of high magnetic field and the corresponding formation of stable white dwarfs, contribution of the magnetic field to the total density and pressure, flux freezing, variation of magnetic field and related currents therein. We also attempt to address the observational connection of such highly magnetized white dwarfs.

A fossil origin for the magnetic field in A stars and white dwarfs

Nature ◽  
2004 ◽  
Vol 431 (7010) ◽  
pp. 819-821 ◽  
Author(s):  
Jonathan Braithwaite ◽  
Hendrik C. Spruit
Keyword(s):  
Magnetic Field ◽  
White Dwarfs ◽  
The Magnetic Field

scholarly journals Dust trajectory simulations around the Sun, Vega, and Fomalhaut

2019 ◽  
Vol 626 ◽  
pp. A107 ◽  
Author(s):  
Johann Stamm ◽  
Andrzej Czechowski ◽  
Ingrid Mann ◽  
Carsten Baumann ◽  
Margaretha Myrvang
Keyword(s):  
Magnetic Field ◽  
Radiation Pressure ◽  
Gravitational Force ◽  
Charged Particles ◽  
Charged Dust ◽  
The Sun ◽  
Pressure Force ◽  
Electromagnetic Forces ◽  
Model Calculations ◽  
Radiation Pressure Force

Context. Vega and Fomalhaut display a thermal emission brightness that could possibly arise from hot dust near the stars, an inner extension of their planetary debris disks. An idea has been suggested that nanometer-sized dust particles are kept in the vicinity of the stars by electromagnetic forces. This resembles the trapping that model calculations show in the corotating magnetic field in the inner heliosphere within approximately 0.2 AU from the Sun. Aims. The aim of this work is to study whether the trapping of dust due to electromagnetic forces acting on charged dust near the Sun can occur around Vega and Fomalhaut and what are the conditions for trapping. Methods. We studied the dust trajectories with numerical calculations of the full equation of motion, as well as by using the guiding center approximation. We assumed a constant dust charge and a Parker-type magnetic field, which we estimated for the two stars. Results. We find no bound trajectories of charged particles around Vega or Fomalhaut as long as the radiation pressure force exceeds the gravitational force, that is, for particles smaller than 1 μm. A trapping zone could exist inside of 0.02 AU for Vega and 0.025 AU for Fomalhaut, but only for those particles with radiation pressure force smaller than gravitational force. In comparison to the Sun, the trapping conditions would occur closer to the stars because their faster rotation leads to a more closely wound-up magnetic field spiral. We also show that plasma corotation can be consistent with trapping. Our model calculations show that the charged particles are accelerated to stellar wind velocity very quickly, pass 1 AU after approximately three days, and are further ejected outward where they pass the debris disks at high velocity. We find this for particles with a surface charge-to-mass ratio larger than 10−6 elementary charges per proton mass for both negatively and positively charged dust and independent of the strength of the radiation pressure force. Based on charging assumptions, this would correspond to dust of sizes 100 nm and smaller.

scholarly journals Cyclotron Line Emission from Accretion onto a Magnetized Neutron Star

1981 ◽  
Vol 93 ◽  
pp. 233-233
Author(s):  
E. E. Salpeter
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Landau Level ◽  
Optical Depth ◽  
Radiative Decay ◽  
Line Emission ◽  
Collisional Excitation ◽  
Magnetic Field Axis ◽  
Cyclotron Line ◽  
The Magnetic Field

For material accreting along the magnetic field axis of a neutron star, electrons are quantized into Landau orbits. Collisional excitation of the first excited Landau level, followed by radiative decay, leads to the emission of a cyclotron line. The expected line is broad, because the optical depth is large, and its shape is difficult to calculate. Redshifts due to the recoil of a scattering electron and blueshifts due to scattering from the infalling accretion column are being calculated by I. Wasserman, as well as the proton stopping length in the presence of a magnetic field.

scholarly journals Improvement of ion acceleration in radiation pressure acceleration regime by using an external strong magnetic field

2019 ◽  
Vol 37 (2) ◽  
pp. 217-222 ◽  
Author(s):  
H. Cheng ◽  
L. H. Cao ◽  
J. X. Gong ◽  
R. Xie ◽  
C. Y. Zheng ◽  
...  
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Laser Pulse ◽  
Radiation Pressure ◽  
Longitudinal Magnetic Field ◽  
Ponderomotive Force ◽  
Two Dimensional ◽  
Particle In Cell ◽  
Combined Action ◽  
The Magnetic Field

AbstractTwo-dimensional particle-in-cell (PIC) simulations have been used to investigate the interaction between a laser pulse and a foil exposed to an external strong longitudinal magnetic field. Compared with that in the absence of the external magnetic field, the divergence of proton with the magnetic field in radiation pressure acceleration (RPA) regimes has improved remarkably due to the restriction of the electron transverse expansion. During the RPA process, the foil develops into a typical bubble-like shape resulting from the combined action of transversal ponderomotive force and instabilities. However, the foil prefers to be in a cone-like shape by using the magnetic field. The dependence of proton divergence on the strength of magnetic field has been studied, and an optimal magnetic field of nearly 60 kT is achieved in these simulations.

scholarly journals Timing analysis of 2S 1417-624 observed with NICER and Insight-HXMT

2019 ◽  
Author(s):  
L Ji ◽  
V Doroshenko ◽  
A Santangelo ◽  
C Güngör ◽  
S Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radiation Pressure ◽  
Timing Analysis ◽  
Theoretical Models ◽  
Accretion Disc ◽  
High Energies ◽  
Timing Properties ◽  
The Magnetic Field

Abstract We present a study of timing properties of the accreting pulsar 2S 1417-624 observed during its 2018 outburst, based on Swift/BAT, Fermi/GBM, Insight-HXMT and NICER observations. We report a dramatic change of the pulse profiles with luminosity. The morphology of the profile in the range 0.2-10.0 keV switches from double to triple peaks at ∼2.5 $\rm \times 10^{37}{\it D}_{10}^2\ erg\ s^{-1}$ and from triple to quadruple peaks at ∼7 $\rm \times 10^{37}{\it D}_{10}^2\ erg\ s^{-1}$. The profile at high energies (25-100 keV) shows significant evolutions as well. We explain this phenomenon according to existing theoretical models. We argue that the first change is related to the transition from the sub to the super-critical accretion regime, while the second to the transition of the accretion disc from the gas-dominated to the radiation pressure-dominated state. Considering the spin-up as well due to the accretion torque, this interpretation allows to estimate the magnetic field self-consistently at ∼7 × 1012 G.

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