Pulsar Magnetic Field Research Articles

Длиннопериодные геомагнитные пульсации как элемент воздействия космической погоды на технологические системы

We analyze variations in geomagnetically induced currents (GIC) and pulsations of the geomagnetic field latitudinal By component in the frequency range 1–20 mHz. The analysis is based on the data from GIC registration at the Kola Peninsula and magnetic data from IMAGE network stations, obtained with 10 s sampling in 2017. This allows us to include pulsations of both Pc5/Pi3 and Pc4/Pi2 frequency range in the analysis and examine polyharmonic pulsations with spectral maxima in both ranges. It is shown that GICs are effectively generated at frequencies above 5 mHz. Polyharmonic pulsations are potentially more dangerous than monoharmonic ones because the ratio of GIC to magnetic field pulsations’ amplitude is higher and the lifetime of unipolar GIC is longer.

Long-period geomagnetic pulsations as an element of the space weather influence on technologocal systems

We analyze variations in geomagnetically induced currents (GIC) and pulsations of the geomagnetic field latitudinal By component in the frequency range 1–20 mHz. The analysis is based on the data from GIC registration at the Kola Peninsula and magnetic data from IMAGE network stations, obtained with 10 s sampling in 2017. This allows us to include pulsations of both Pc5/Pi3 and Pc4/Pi2 frequency range in the analysis and examine polyharmonic pulsations with spectral maxima in both ranges. It is shown that GICs are effectively generated at frequencies above 5 mHz. Polyharmonic pulsations are potentially more dangerous than monoharmonic ones because the ratio of GIC to magnetic field pulsations’ amplitude is higher and the lifetime of unipolar GIC is longer.

Rotating Vector Model and Radius-to-frequency Mapping in the Presence of a Multipole Magnetic Field

The rotating vector model and radius-to-frequency mapping in the presence of a multipole magnetic field in pulsars and magnetars are considered. An axisymmetric potential field is assumed, and the following is found: (1) The radiation beam in the case of a multipole field is wider than the dipole case. This may account for the increasing pulse width at the higher frequency of pulsars (anti-radius-to-frequency mapping); (2) The expression for the polarization position angle is unchanged. Only the inclination angle α and phase constant ϕ 0 will change. The angle between the rotational axis and line of sight and the position angle constant ψ 0 will not change. When fitting the varying position angle of magnetars, these constraints should be considered. The appearance and disappearance of a multipole field may account for the changing slope of the position angle in the radio-emitting magnetar Swift J1818.0–1607. A similar but more active process in magnetar magnetospheres may account for the diverse position angle in fast radio bursts.

Influence of Space Curvature on the Moment of Inertia of a Pulsar Magnetic Field

We consider the influence of space curvature in the Schwarzschild metric on the contribution of the magnetic field outside the neutron star to the moment of inertia of a radio pulsar. Our considerationis restricted only to the simplest configuration of the magnetic field, when it can be described by only one harmonic. We show that at a fixed magnetic field strength on the stellar surface the influence of space curvature reduces the contribution of the magnetic field outside the star to the departure of the inertia tensor from the spherical one several-fold.

Quasiperiodic ELF/VLF Emissions Associated With Corresponding Pulsations of the Geomagnetic Field

AbstractWe present a comparison between properties of quasiperiodic (QP) extra low frequency/very low frequency emissions observed by the low‐altitude DEMETER spacecraft and ultra‐low frequency (ULF) geomagnetic field pulsations measured on the ground by the Canadian Array for Realtime Investigations of Magnetic Activity system of flux‐gate magnetometers and by the Sodankylä Geophysical Observatory magnetometer. Altogether, we have analyzed 398 QP events observed at the times when DEMETER was close to the ground‐based magnetometers. The modulation periods of the analyzed QP events were larger than 10 s and their frequency bandwidths were larger than 200 Hz. For a part of QP emissions with modulation periods about 30 s, there was a good agreement between the modulation periods and peak frequencies of ULF magnetic field pulsations measured on the ground. These QP emissions appear to be closely associated with coincident geomagnetic pulsations (QP1 type), and they represent ∼18% of the total number of analyzed QP events. No corresponding geomagnetic pulsations were identified in the remaining 82% of QP events (QP2 type). The intensity of QP1 events does not seem to correlate with the intensity of geomagnetic field pulsations, while the intensity of QP2 events increases with the integral intensity of geomagnetic field pulsations. Based on the observed association between QP emissions and geomagnetic field pulsations, we estimate the radial distance of the generation region of QP1 emissions to L ∼ 7.

Broadband X-Ray Spectroscopy of the Pulsar Wind Nebula in HESS J1640-465

We present updated measurements of the X-ray properties of the pulsar wind nebula associated with the TeV γ-ray source HESS J1640-465 derived from Chandra and Nuclear Spectroscopic Telescope Array data. We report a high N H value along the line of sight, consistent with previous work, which led us to incorporate the effects of dust scattering in our spectral analysis. Due to uncertainties in the dust scattering, we report a range of values for the PWN properties (photon index and unabsorbed flux). In addition, we fit the broadband spectrum of this source and found evidence for spectral softening and decreasing unasborbed flux as we go to higher photon energies. We then used a one-zone time-dependent evolutionary model to reproduce the dynamical and multiwavelength spectral properties of our source. Our model suggests a short spin-down timescale, a relatively higher than average magnetized pulsar wind, a strong pulsar wind nebula magnetic field and maximum electron energy up to PeV, suggesting HESS J1640-465 could be a PeVatron candidate.

Substorm Induced Nighttime Plasma Flow Pulsations Observed by ROCSAT‐1 at Topside Ionosphere

The Republic of China Satellite-1 orbiting at 600 km topside ionosphere has observed the topside ionospheric plasma flow pulsations induced by the substorm onsets. These pulsation events indicated that the plasma flow pulsations mainly oscillate in the two mutually perpendicular directions with respect to the geomagnetic field lines. The field-aligned flow as well as the ion density indicates almost no variation. This implies that the pulsation events are of Alfven wave in nature. The Hilbert-Huang transform analysis is applied to study the dominant wave frequencies and the polarization in the two perpendicular components of plasma flows (i.e., the perturbed electric/magnetic fields). The hodograms of the polarization in the Pi1 frequency is shown to be linearly polarized, while the left-handed polarization is seen in the Pi2 frequencies that are in harmonic relationship. These plasma flow pulsations in the nighttime topside ionosphere are caused by the field-line-resonance magnetic field pulsations converted from the inward propagated compressional disturbance across the nighttime magnetosphere/plasmasphere which is originated at the near-Earth magnetotail at the substorm onset.

A short review on the pulsar magnetic inclination angles

AbstractThe inclination angle χ between the magnetic and rotation axes of pulsars is an important parameter in pulsar physics. The changes in the inclination angle of a pulsar would lead to observable effects, such as changes in the pulse beam width and braking index of the star. In this paper, we perform a short review on the evolution of a pulsar's magnetic inclination angle, as well as the latest research progress. Using an alignment rotator model in a vacuum, we investigate the magnetic inclination angle change rates for 12 high‐braking index pulsars without a glitch, whose timing observations are obtained using the Nanshan 25‐m Radio Telescope at Xinjiang Astronomical Observatory. For our purpose, three representative pulsars J0157+6212, J1743−3150, and J1857+0526 are chosen and their rotation and inclination angle evolutions are further investigated. In the future, radio and x‐ray polarimetric observations will provide more information about the inclination angles of pulsars, which could help us understand the origin of the variations in χ of pulsars and shed light on the range of possibilities of pulsar magnetic field configuration. A continuous study of the pulsar inclination angle will provide an important window into additional physical processes at work in the young and highly magnetized pulsars.

Transient Flashes in Saturn’s UV Aurora: An Analysis of Hubble Space Telescope 2013–2017 Campaigns and Cassini Magnetic Field Measurements

We examined Hubble Space Telescope images of Saturn’s northern UV aurora in 2013–2017, identified 29 short-lived flashes, and examined simultaneous magnetometer data collected by the Cassini orbiter. When observation cadence permitted, a flash lifetime of 4–17 min (subject to exposure time-related uncertainties), and a 40–70 min recurrence period were found. An occurrence map shows a strong preference in both local time (14–19 LT) and latitude (75–85°). These transient flashes are identified in both the presence and absence of Saturn’s main auroral oval, indicating the lack of dependence on the main emission power. The concurrent magnetic field pulsations generally form a sawtooth shape, and the local field strength experiences a change of 0.2 to 2.0 nT (depending on the distance of Cassini). The quasiperiodic pulsation events were all detected when the spacecraft was in the southern hemisphere with conjugate flashes in northern aurora, suggesting these events occur on closed field lines, and typically showing a sudden transition to a less lagging, more southward magnetic field configuration. We also found the ionospheric footprint of the spacecraft must be close to the region of flashes for magnetic field pulsations to be detected, implying a localised rather than global driving process.

Long-period Pulsars as Possible Outcomes of Supernova Fallback Accretion

For about half a century, the radio pulsar population was observed to spin in the ∼0.002–12 s range, with different pulsar classes having a spin-period evolution that differs substantially depending on their magnetic fields or past accretion history. The recent detection of several slowly rotating pulsars has reopened the long-standing question of the exact physics, and observational biases, driving the upper bound of the period range of the pulsar population. In this work, we perform a parameter study of the spin-period evolution of pulsars interacting with supernova fallback matter and specifically look at the fallback accretion disk scenario. Depending on the initial conditions at formation, this evolution can differ substantially from the typical dipolar spin-down, resulting in pulsars that show spin periods longer than their coeval peers. By using general assumptions for the pulsar spin period and magnetic field at birth, initial fallback accretion rates, and including magnetic field decay, we find that very long spin periods (≳100 s) can be reached in the presence of strong, magnetar-like magnetic fields (≳1014 G) and moderate initial fallback accretion rates (∼1022−1027 g s−1). In addition, we study the cases of two recently discovered periodic radio sources, the pulsar PSR J0901–4046 (P = 75.9 s) and the radio transient GLEAM-X J162759.5–523504.3 (P = 1091 s), in light of our model. We conclude that the supernova fallback scenario could represent a viable channel to produce a population of long-period isolated pulsars that only recent observation campaigns are starting to unveil.

Features of Turbulence Excited by Pulsed High-Frequency Pump in a Magnetoplasma

Turbulence developed in a magnetoplasma modified by a high-power high-frequency pulse fed to a loop antenna is discovered and studied on the large-scale KROT plasma device. Turbulence is manifested in the excitation of the electron density and magnetic field pulsations, deep self-modulation of the pump wave, and modulation of probe waves passing through the modified plasma region. The space–time characteristics of turbulence are determined using correlated plasma density measurements by a pair of miniature microwave resonator probes and a magnetic probe. It is established that turbulence is excited only in the transparency band of the dense magnetoplasma to electromagnetic radiation: turbulent perturbations of the density and magnetic field exist during pumping at frequencies lower than the electron cyclotron frequency and are absent at pumping frequencies exceeding the electron cyclotron frequency.

Initial periods and magnetic fields of neutron stars

ABSTRACT Initial distributions of pulsar periods and magnetic fields are essential components of multiple modern astrophysical models. Not enough work has been done to properly constrain these distributions using direct measurements. Here, we aim to fill this gap by rigorously analysing the properties of young neutron stars (NSs) associated to supernova remnants (SNRs). In order to perform this task, we compile a catalogue of 56 NSs uniquely paired to SNRs with known age estimate. Further, we analyse this catalogue using multiple statistical techniques. We found that distribution of magnetic fields and periods for radio pulsars are both well described using the lognormal distribution. The mean magnetic field is log10[B/G] = 12.44 and standard deviation is σB = 0.44. Magnetars and central compact objects do not follow the same distribution. The mean initial period is $\log _{10} P_0 [P / \mathrm{s}] = -1.04_{-0.2}^{+0.15}$ and standard deviation is $\sigma _{\rm p} = 0.53_{-0.08}^{+0.12}$. We show that the normal distribution does not describe the initial periods of NSs sufficiently well. Parameters of the initial period distribution are not sensitive to the exact value of the braking index.

Axion production in pulsar magnetosphere gaps

Pulsar magnetospheres admit non-stationary vacuum gaps that are characterized by non-vanishing ${\bf{E}} \cdot {\bf{B}}$. The vacuum gaps play an important role in plasma production and electromagnetic wave emission. We show that these gaps generate axions whose energy is set by the gap oscillation frequency. The density of axions produced in a gap can be several orders of magnitude greater than the ambient dark matter density. In the strong pulsar magnetic field, a fraction of these axions may convert to photons, giving rise to broadband radio signals. We show that dedicated observations of nearby pulsars with radio telescopes (FAST) and interferometers (SKA) can probe axion-photon couplings that are a few orders of magnitude lower than current astrophysical bounds.

Even moderate geomagnetic pulsations can cause fluctuations of <i>fo</i>F2 frequency of the auroral ionosphere

Abstract. The ionosonde at the Sodankylä Geophysical Observatory (SOD; 67∘ N, 27∘ E; Finland) routinely performs vertical sounding once per minute which enables the study of fast ionospheric variations at a frequency of the long-period geomagnetic pulsations Pc5–6/Pi3 (1–5 mHz). Using the ionosonde data from April 2014–December 2015 and colocated geomagnetic measurements, we have investigated a correspondence between the magnetic field pulsations and variations of the critical frequency of radio waves reflected from the ionospheric F2 layer (foF2). For this study, we have developed a technique for automated retrieval of the critical frequency of the F2 layer from ionograms. As a rule, the Pc5–6/Pi3 frequency band fluctuations in foF2 were observed at daytime during quiet or moderately disturbed space weather conditions. In most cases (about 80 %), the coherence between the foF2 variations and geomagnetic pulsations was low. However in some cases (specified as “coherent”) the coherence was as large as γ2≥0.5. The following conditions are favorable for the occurrence of coherent cases: enhanced auroral activity (6 h maximal auroral electrojet (AE) ≥800 nT), high solar wind speed (V>600 km/s), fluctuating solar wind pressure and northward interplanetary magnetic field. In the cases when the coherence was higher at shorter periods of oscillations, the magnetic pulsations demonstrated features typical for the Alfvén field line resonance.

Self-Powered Diagnostic System for AC Machines Based on Inhomogeneity of Magnetic Field Distribution in Air Gap

This article presents a self-powered system for supplying rotor measurement equipment and detecting stator winding inter-turn short circuit, and broken rotor bar faults in AC Machines. This system uses harvesting coils to harvest air-gap magnetic field pulsation and generate energy for powering equipment installed on the rotor. Furthermore, installing this system on the stator or rotor of AC machines provides a voltage signal appropriate for fault detection purposes. To determine specifications of the harvesting coils – coils turn numbers, and their optimal mounting positions – numerous finite element simulations have been carried out. In addition, a fault detection method has been proposed to detect broken rotor bar and inter-turn short circuit faults using induced voltage in the harvesting coils. To verify the performance of the proposed system, some experimental and simulation tests have been performed on various AC machines. The results have confirmed the applicability of this system in self-powering applications and fault detection purposes.

Testing the fossil field hypothesis: could strongly magnetized OB stars produce all known magnetars?

ABSTRACT Stars of spectral types O and B produce neutron stars (NSs) after supernova explosions. Most of NSs are strongly magnetized including normal radio pulsars with B ∝ 1012 G and magnetars with B ∝ 1014 G. A fraction of 7–12 per cent of massive stars are also magnetized with B ∝ 103 G and some are weakly magnetized with B ∝ 1 G. It was suggested that magnetic fields of NSs could be the fossil remnants of magnetic fields of their progenitors. This work is dedicated to study this hypothesis. First, we gather all modern precise measurements of surface magnetic fields in O, B, and A stars. Secondly, we estimate parameters for lognormal distribution of magnetic fields in B stars and found μB = 2.83 ± 0.1 log10 (G), σB = 0.65 ± 0.09 for strongly magnetized and μB = 0.14 ± 0.5 log10 (G), $\sigma =0.7_{-0.27}^{+0.57}$ for weakly magnetized. Third, we assume that the magnetic field of pulsars and magnetars have 2.7-dex difference in magnetic fields and magnetars represent 10 per cent of all young NSs and run population synthesis. We found that it is impossible to simultaneously reproduce pulsars and magnetars populations if the difference in their magnetic fields is 2.7 dex. Therefore, we conclude that the simple fossil origin of the magnetic field is not viable for NSs.

Multipoint Observations of Quasiperiodic Emission Intensification and Effects on Energetic Electron Precipitation

AbstractThe two Van Allen Probes simultaneously recorded a coherently modulated quasiperiodic (QP) emission that persisted for 3 h. The magnetic field pulsation at the locations of the two satellites showed a substantial difference, and their frequencies were close to but did not exactly match the repetition frequency of QP emissions for most of the time, suggesting that those coherent QP emissions probably originated from a common source, which then propagated over a broad area in the magnetosphere. The QP emissions were amplified by local anisotropic electron distributions, and their large‐scale amplitudes were modulated by the plasma density. A novel observation of this event is that chorus waves at frequencies above QP emissions exhibit a strong correlation with QP emissions. Those chorus waves intensified when the QP emissions reach their peak frequency. This indicates that embryonic QP emissions may be critical for its own intensification as well as chorus waves under certain circumstances. A Low‐Earth‐Orbit POES satellite observed enhanced energetic electron precipitation in conjunction with the Van Allen Probes, providing direct evidence that QP emissions precipitate energetic electrons into the atmosphere. This scenario is quantitatively confirmed by our quasilinear diffusion simulation results.

NICER Discovery of Millisecond X-Ray Pulsations and an Ultracompact Orbit in IGR J17494-3030

Abstract We report the detection of 376.05 Hz (2.66 ms) coherent X-ray pulsations in NICER observations of a transient outburst of the low-mass X-ray binary IGR J17494−3030 in 2020 October/November. The system is an accreting millisecond X-ray pulsar in a 75-minute ultracompact binary. The mass donor is most likely a ≃0.02 M ⊙ finite-entropy white dwarf composed of He or C/O. The fractional rms pulsed amplitude is 7.4%, and the soft (1–3 keV) X-ray pulse profile contains a significant second harmonic. The pulsed amplitude and pulse phase lag (relative to our mean timing model) are energy dependent, each having a local maximum at 4 and 1.5 keV, respectively. We also recovered the X-ray pulsations in archival 2012 XMM-Newton observations, allowing us to measure a long-term pulsar spin-down rate of Hz s−1 and to infer a pulsar surface dipole magnetic field strength of ≃109 G. We show that the mass transfer in the binary is likely nonconservative, and we discuss various scenarios for mass loss from the system.

MHD grid-turbulence in a closed decaying flow of liquid sodium

Grid-induced turbulent flows of liquid sodium in a toroidal channel at high Reynolds numbers and moderate magnetic Reynolds numbers are studied experimentally. Grids with a pitch of 15 mm and 31 mm were used, and one or two grids were installed in the channel. It is shown that the dynamics of the pulsed turbulent flow in the channel with grids differs significantly from that observed in a free channel, where the turbulence develops on the scale of the channel cross-section. Measurements of the characteristics of velocity and magnetic field pulsations have shown that induction effects in the unsteady pulse flow have time to manifest themselves in full. The spectra of velocity and magnetic field pulsations are obtained.

Simultaneous Observations of ELF/VLF Rising‐Tone Quasiperiodic Waves and Energetic Electron Precipitations in the High‐Latitude Upper Ionosphere

AbstractThe quasiperiodic (QP) waves accompanied by simultaneous energetic electron precipitations in the high‐latitude ionosphere were recorded by the sun‐synchronous circular orbit China Seismo‐Electromagnetic Satellite (CSES). The new features of QP waves observed by CSES are the well‐pronounced rising‐tone structures and very short repetition periods, which are not ofen reported by previous studies. The repetition period of QP waves varies from ~1 to over 20 s, with wave spectral properties displaying dynamic structures and clear cutoff frequencies. The majority of QP waves appear at geomagnetic latitudes from ~50° to 65°, and L shell from ~3.5 to 4, mostly inside the plasmapause. The QP waves obliquely propagate towards decreasing L shell directions with right‐handed polarization, with wave normal angles varying from ~30° to 50°. Out of the 68 events examined, 19 of them show synchronous variations of ultralow frequency (ULF) magnetic field pulsations in certain portions of the wave event. The energetic electrons predominately precipitate in a double‐peak pattern (~400 to 550 keV and ~700 to 800 keV). No clear periodic precipitating fluxes were found. The estimated time interval of energetic electrons driving free energy to modulate the whistler‐mode waves varies from 0.04 to 30°s, which is roughly consistent with the observed repetition periods (10 to over 20 s). For the fast repetition period (~1 to 2s) QP wave, it is likely caused by the bouncing of the extremely/very low frequency (ELF/VLF) whistler‐mode wave packets from the conjugate ionosphere.