Swift/BAT measurements of the cyclotron line energy decay in the accreting neutron star Hercules X-1: indication of an evolution of 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.

Download Full-text

First characterization of Swift J1845.7–0037 with NuSTAR

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937036 ◽

2020 ◽

Vol 634 ◽

pp. A89

Author(s):

V. Doroshenko ◽

S. Tsygankov ◽

J. Long ◽

A. Santangelo ◽

S. Molkov ◽

...

Keyword(s):

Magnetic Field ◽

Spectral Analysis ◽

Neutron Star ◽

X Ray ◽

Transient Source ◽

Broadband Spectrum ◽

Cyclotron Line ◽

The Magnetic Field

The hard X-ray transient source Swift J1845.7–0037 was discovered in 2012 by Swift/BAT. However, at that time, no dedicated observations of the source were performed. In October 2019, the source became active again, and X-ray pulsations with a period of ∼199 s were detected with Swift/XRT. This triggered follow-up observations with NuSTAR. Here, we report on the timing and spectral analysis of the source properties using NuSTAR and Swift/XRT. The main goal was to confirm pulsations and search for possible cyclotron lines in the broadband spectrum of the source to probe its magnetic field. Despite highly significant pulsations with period of 207.379(2) s being detected, no evidence for a cyclotron line was found in the spectrum of the source. We therefore discuss the strength of the magnetic field based on the source flux and the detection of the transition to the “cold-disc” accretion regime during the 2012 outburst. Our conclusion is that the source is most likely a highly magnetized neutron star with B ≳ 1013 G at a large distance of d ∼ 10 kpc. The latter is consistent with the nondetection of a cyclotron line in the NuSTAR energy band.

Download Full-text

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935507 ◽

2019 ◽

Vol 626 ◽

pp. A106 ◽

Cited By ~ 6

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.

Download Full-text

Effect of magnetic field on the burning of a neutron star

International Journal of Modern Physics E ◽

10.1142/s0218301318500830 ◽

2018 ◽

Vol 27 (10) ◽

pp. 1850083 ◽

Cited By ~ 3

Author(s):

Ritam Mallick ◽

Amit Singh

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Initial Density ◽

Considerable Effect ◽

Magnetic Axis ◽

Small Window ◽

Exothermic Process ◽

Text Density ◽

The Magnetic Field ◽

Observational Aspect

In this paper, we present the effect of a strong magnetic field in the burning of a neutron star (NS). We have used relativistic magneto-hydrostatic (MHS) conservation equations for studying the PT from nuclear matter (NM) to quark matter (QM). We found that the shock-induced phase transition (PT) is likely if the density of the star core is more than three times nuclear saturation ([Formula: see text]) density. The conversion process from NS to quark star (QS) is found to be an exothermic process beyond such densities. The burning process at the star center most likely starts as a deflagration process. However, there can be a small window at lower densities where the process can be a detonation one. At small enough infalling matter velocities the resultant magnetic field of the QS is lower than that of the NS. However, for a higher value of infalling matter velocities, the magnetic field of QM becomes larger. Therefore, depending on the initial density fluctuation and on whether the PT is a violent one or not the QS could be more magnetic or less magnetic. The PT also have a considerable effect on the tilt of the magnetic axis of the star. For smaller velocities and densities the magnetic angle are not affected much but for higher infalling velocities tilt of the magnetic axis changes suddenly. The magnetic field strength and the change in the tilt axis can have a significant effect on the observational aspect of the magnetars.

Download Full-text

Estimation of Electrical Conductivity and Magnetization Parameter of Neutron Star Crusts and Applied to the High-Braking-Index Pulsar PSR J1640-4631

Universe ◽

10.3390/universe6050063 ◽

2020 ◽

Vol 6 (5) ◽

pp. 63

Author(s):

Hui Wang ◽

Zhi-Fu Gao ◽

Huan-Yu Jia ◽

Na Wang ◽

Xiang-Dong Li

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Neutron Stars ◽

General Expression ◽

Equations Of State ◽

Rotation Period ◽

Ohmic Dissipation ◽

Hartree Fock ◽

Induction Equation ◽

The Magnetic Field

Young pulsars are thought to be highly magnetized neutron stars (NSs). The crustal magnetic field of a NS usually decays at different timescales in the forms of Hall drift and Ohmic dissipation. The magnetization parameter ω B τ is defined as the ratio of the Ohmic timescale τ O h m to the Hall drift timescale τ H a l l . During the first several million years, the inner temperature of the newly born neutron star cools from T = 10 9 K to T = 1.0 × 10 8 K, and the crustal conductivity increases by three orders of magnitude. In this work, we adopt a unified equations of state for cold non-accreting neutron stars with the Hartree–Fock–Bogoliubov method, developed by Pearson et al. (2018), and choose two fiducial dipole magnetic fields of B = 1.0 × 10 13 G and B = 1.0 × 10 14 G, four different temperatures, T, and two different impurity concentration parameters, Q, and then calculate the conductivity of the inner crust of NSs and give a general expression of magnetization parameter for young pulsars: ω B τ ≃ ( 1 − 50 ) B 0 / ( 10 13 G) by using numerical simulations. It was found when B ≤ 10 15 G, due to the quantum effects, the conductivity increases slightly with the increase in the magnetic field, the enhanced magnetic field has a small effect on the matter in the low-density regions of the crust, and almost has no influence the matter in the high-density regions. Then, we apply the general expression of the magnetization parameter to the high braking-index pulsar PSR J1640-4631. By combining the observed arrival time parameters of PSR J1640-4631 with the magnetic induction equation, we estimated the initial rotation period P 0 , the initial dipole magnetic field B 0 , the Ohm dissipation timescale τ O h m and Hall drift timescale τ H a l l . We model the magnetic field evolution and the braking-index evolution of the pulsar and compare the results with its observations. It is expected that the results of this paper can be applied to more young pulsars.

Download Full-text

Cyclotron lines in highly magnetized neutron stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834479 ◽

2019 ◽

Vol 622 ◽

pp. A61 ◽

Cited By ~ 34

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.

Download Full-text

Two-fluid simulations of the magnetic field evolution in neutron star cores in the weak-coupling regime

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2543 ◽

2020 ◽

Vol 498 (2) ◽

pp. 3000-3012 ◽

Cited By ~ 2

Author(s):

F Castillo ◽

A Reisenegger ◽

J A Valdivia

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Charged Particles ◽

Stable Stratification ◽

Composition Gradient ◽

Axially Symmetric ◽

Drag Forces ◽

Degeneracy Pressure ◽

The Magnetic Field ◽

Two Fluid

ABSTRACT In a previous paper, we reported simulations of the evolution of the magnetic field in neutron star (NS) cores through ambipolar diffusion, taking the neutrons as a motionless uniform background. However, in real NSs, neutrons are free to move, and a strong composition gradient leads to stable stratification (stability against convective motions) both of which might impact on the time-scales of evolution. Here, we address these issues by providing the first long-term two-fluid simulations of the evolution of an axially symmetric magnetic field in a neutron star core composed of neutrons, protons, and electrons with density and composition gradients. Again, we find that the magnetic field evolves towards barotropic ‘Grad–Shafranov equillibria’, in which the magnetic force is balanced by the degeneracy pressure gradient and gravitational force of the charged particles. However, the evolution is found to be faster than in the case of motionless neutrons, as the movement of charged particles (which are coupled to the magnetic field, but are also limited by the collisional drag forces exerted by neutrons) is less constrained, since neutrons are now allowed to move. The possible impact of non-axisymmetric instabilities on these equilibria, as well as beta decays, proton superconductivity, and neutron superfluidity, are left for future work.

Download Full-text

Hydrogen molecular ion in the magnetic field of a neutron star

Astrophysics and Space Science ◽

10.1007/bf00653750 ◽

1984 ◽

Vol 103 (2) ◽

pp. 357-370 ◽

Cited By ~ 14

Author(s):

V. K. Khersonskij

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Hydrogen Molecular Ion ◽

Molecular Ion ◽

The Magnetic Field

Download Full-text

Early neutron star evolution in high-mass X-ray binaries

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa675 ◽

2020 ◽

Vol 494 (1) ◽

pp. 44-49 ◽

Cited By ~ 2

Author(s):

Wynn C G Ho ◽

M J P Wijngaarden ◽

Nils Andersson ◽

Thomas M Tauris ◽

F Haberl

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Thermal Emission ◽

Equilibrium Phase ◽

High Mass ◽

X Ray ◽

Spin Period ◽

Long Duration ◽

X Ray Binaries ◽

The Magnetic Field

ABSTRACT The application of standard accretion theory to observations of X-ray binaries provides valuable insights into neutron star (NS) properties, such as their spin period and magnetic field. However, most studies concentrate on relatively old systems, where the NS is in its late propeller, accretor, or nearly spin equilibrium phase. Here, we use an analytic model from standard accretion theory to illustrate the evolution of high-mass X-ray binaries (HMXBs) early in their life. We show that a young NS is unlikely to be an accretor because of the long duration of ejector and propeller phases. We apply the model to the recently discovered ∼4000 yr old HMXB XMMU J051342.6−672412 and find that the system’s NS, with a tentative spin period of 4.4 s, cannot be in the accretor phase and has a magnetic field B > a few × 1013 G, which is comparable to the magnetic field of many older HMXBs and is much higher than the spin equilibrium inferred value of a few × 1011 G. The observed X-ray luminosity could be the result of thermal emission from a young cooling magnetic NS or a small amount of accretion that can occur in the propeller phase.

Download Full-text

Radiation Beaming in Pulsars

Symposium - International Astronomical Union ◽

10.1017/s0074180900007816 ◽

1971 ◽

Vol 46 ◽

pp. 455-456

Author(s):

V. Canuto

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Coming Out ◽

Critical Magnetic Field ◽

Zero Field ◽

Ordinary Wave ◽

Magnetic Field Axis ◽

Field Lines ◽

Star Surface ◽

The Magnetic Field

It is usually considered that the beaming of the radiation coming out of a pulsar has to be strictly connected with the mechanism producing the radiation itself. We want to show that even when the emitting mechanism gives rise to an isotropically distributed radiation, the presence of a strong magnetic field will automatically beam the radiation preferentially along the magnetic field line rather than in any other direction. We have computed the Compton scattering and from that the opacity KH (K0 is the opacity for zero field). In Figure 1 the ratio KH/K0 is given vs. θ, the angle between the propagation vector and the magnetic field axis. Hq is a critical magnetic field numerically equal to 4.41 × 1013 G; Ne is the electron density. For the ordinary wave the opacity is reduced at θ = 0, while it is unaffected at θ = π/2 where KH → K0. Even at θ = π/4 the ratio KH/K0 is still ≃ 10−2, and a good beaming is still present. The values of the parameters are proper for a neutron star surface. It is to be noticed that the ratio KH/K0 is of the order of (ω/ωH)2 or [(kT/mc2)/(H/Hq]2. One therefore can conclude that the presence of a magnetic field itself assures the beaming of radiation along the field lines.

Download Full-text