Search

The neutrino-driven wind cooling phase of proto-neutron stars (PNSs) follows successful supernovae. Wind models without magnetic fields or rotation fail to achieve the necessary conditions for production of the third r -process peak, but robustly produce a weak r- process in neutron-rich winds. Using 2D magnetohydrodynamic simulations with magnetar-strength magnetic fields and rotation, we show that the PNS rotation rate significantly affects the thermodynamic conditions of the wind. We show that high-entropy material is quasiperiodically ejected from the closed zone of the PNS magnetosphere with the required thermodynamic conditions to produce heavy elements. We show that maximum entropy S of the material ejected depends systematically on the magnetar spin period P ⋆ and scales as S ∝ P ⋆ − 5 / 6 for sufficiently rapid rotation. We present results from simulations at a constant neutrino luminosity representative of ∼1–2 s after the onset of cooling for P ⋆ ranging from 5–200 ms and a few simulations with evolving neutrino luminosity where we follow the evolution of the magnetar wind until 10–14 s after the onset of cooling. We estimate at magnetar polar magnetic field strength B 0 = 3 × 1015 G and 1015 G that neutron-rich magnetar winds can, respectively, produce at least ∼1–5 × 10−5 M ⊙ and ∼1–4 × 10−7 M ⊙ of material with the required parameters for synthesis of the third r -process peak, within 1–2 s and 10 s, respectively, in that order after the onset of cooling. We show that proton-rich magnetar winds can have favorable conditions for production of p- nuclei, even at a modest B 0 = 5 × 1014 G. [ABSTRACT FROM AUTHOR]

Among the more than 60 sources observed in the first two years of operations, IXPE addressed four magnetars, neutron stars believed to host ultra-strong magnetic fields. We report here the main implication coming from IXPE measurements for the physics of magnetars. Polarimetric observations confirmed the expectations of high polarization degrees, up to ≈ 80 % , values which have not been detected in any other source so far, providing further proof (independent from the P- P ˙ estimate) that magnetars host indeed ultra-magnetized neutron stars. Polarization measurements also indicate that softer X-rays likely come from surface regions where the overlying atmosphere underwent magnetic condensation. The agreement of the phase-dependent polarization angle with a simple rotating vector model strongly supports the presence of vacuum birefringence around the star. [ABSTRACT FROM AUTHOR]

Utilizing four archival X-ray data sets taken with the Hard X-ray Detector onboard Suzaku , timing studies were performed on three magnetars, 1E 1841−045 (observed in 2006), SGR 0501+4516 (2008), and 1RXS J170849.0−400910 (2009 and 2010). Their pulsations were reconfirmed, typically in an energy range of 12–50 keV. The 11.783 s pulses of 1E 1841−045 and those of SGR 0501+4516 at 5.762 s were periodically phase modulated, with a long period of |$\approx 23.4$| and |$\approx 16.4$|  ks, respectively. The pulse-phase modulation was also observed, at |$\approx 46.5$|  ks, from two data sets of 1RXS J170849.0−400910. In all these cases, the modulation amplitude was 6 per cent to 16 per cent of the pulse cycle. Including previously confirmed four objects, this characteristic timing behaviour is now detected from seven magnetars in total, and interpreted as a result of free precession of neutron stars that are deformed to an asphericity of |$\sim 10^{-4}$|⁠. Assuming that the deformation is due to magnetic stress, these magnetars are inferred to harbour toroidal magnetic fields of |$B_{\rm t}\sim 10^{16}$|  G. By comparing the estimated |$B_{\rm t}$| of these objects with their poloidal dipole field |$B_{\rm d}$|⁠ , the |$B_{\rm t}/B_{\rm d}$| ratio is found to increase with their characteristic age. Therefore, the toroidal fields of magnetars are likely to last longer than their poloidal fields. This explains the presence of some classes of neutron stars that have relatively weak |$B_{\rm d}$| but are suspected to hide strong |$B_{\rm t}$| inside them. [ABSTRACT FROM AUTHOR]

Four X-ray datasets of the soft gamma repeater SGR 1806−20, taken with the Gas Imaging Spectrometer (GIS) onboad ASCA, were analyzed. Three of them were acquired over 1993 October 9–20, the last one in 1995 October. Epoch-folding analysis of the 2.8–12 keV signals confirmed the ∼7.6 s pulses in these data, which Kouveliotou et al. (1998, Nature, 393, 235) reported as one of the earliest pulse detections from this object. In the 1995 observation, 3–12 keV pulses were phase modulated with a period of T  = 16.4 ± 0.4 ks, and an amplitude of ∼1 s. This makes a fourth example of the behavior observed from magnetars. As in the previous three sources, the pulse-phase modulation of SGR 1806−20 disappeared at ≲2.5 keV, where the soft X-ray component dominates. In the 1993 datasets, this periodic modulation was reconfirmed, and successfully phase-connected coherently across the 11 d interval. As a result, the modulation period was refined to T  = 16.435 ± 0.024 ks. The implied high stability of the phenomenon strengthens its interpretation in terms of free precession of the neutron star, which is deformed to an asphericity of ∼10−4, presumably by the stress of toroidal magnetic fields reaching ∼1016 G. Toroidal fields of this level can be common among magnetars. [ABSTRACT FROM AUTHOR]

Magnetars are slowly rotating neutron stars that possess the strongest magnetic fields known in the cosmos (1014 − 1015 G). They display a range of transient high-energy electromagnetic activity. The brightest and most energetic of these events are the gamma-ray bursts (GRBs) known as magnetar giant flares (MGFs), with isotropic energies Eiso ≈ 1044 − 1046 erg. Only seven MGF detections have been made to date: three unambiguous events occurred in our Galaxy and the Magellanic Clouds, and the other four MGF candidates are associated with nearby star-forming galaxies. As all seven identified MGFs are bright at Earth, additional weaker events likely remain unidentified in archival data. We conducted a search of the Fermi Gamma-ray Burst Monitor database for candidate extragalactic MGFs and, when possible, collected localization data from the Interplanetary Network (IPN) satellites. Our search yielded one convincing event, GRB 180128A. IPN localizes this burst within NGC 253, commonly known as the Sculptor Galaxy. The event is the second MGF in modern astronomy to be associated with this galaxy and the first time two bursts have been associated with a single galaxy outside our own. Here we detail the archival search criteria that uncovered this event and its spectral and temporal properties, which are consistent with expectations for a MGF. We also discuss the theoretical implications and finer burst structures resolved from various binning methods. Our analysis provides observational evidence of an eighth identified MGF. [ABSTRACT FROM AUTHOR]

Fast radio bursts (FRBs) are cosmological radio transients with millisecond durations and extremely high brightness temperatures. One FRB repeater, FRB 180916.J0158+65 (FRB 180916B), was confirmed to appear 16.35-day periodic activities with 5-day activity window. Another FRB repeater, FRB 121102, and two soft gamma-ray repeaters (SGRs), SGR 1935+2154 and SGR 1806−20, also show possible periodic activities. These periodicities might originate from the precession process of young magnetars due to the anisotropic pressure from the inner magnetic fields as proposed in the literature. In this work, we analyse a self-consistent model for the rotation evolution of magnetars and obtain the evolutions of magnetar precession and obliquity. We find that if the FRB repeaters and the SGRs with (possible) periodic activities originate from the magnetar precession, their ages would be constrained to be hundreds to tens of thousands of years, which is consistent with the typical ages of magnetars. Assuming that the FRB emission is beaming in the magnetosphere as proposed in the literature, we calculate the evolution of the observable probability and the duty cycle of the active window period. We find that for a given magnetar the observable probability increases with the magnetar age in the early stage and decreases with the magnetar age in the later stage; meanwhile, there are one or two active windows in one precession period if the emission is not perfectly axisymmetric with respect to the deformation axis of a magnetar, which could be tested by the future observation for repeating FRB sources. [ABSTRACT FROM AUTHOR]

Recently, two ultralong-period radio transients, GLEAM-X J162759.5-523504.3 (J1627) and GPM J1839-10 (J1839), were discovered with spin periods longer than 1000 s. The origin of these two ultralong-period radio transients is intriguing in understanding the spin evolution of neutron stars (NSs). In this work, we examine whether the interaction between strong magnetized NSs and fallback disks can spin NSs down to the observed ultralong period. Our simulations found that the magnetar + fallback disk model can account for the observed period, period derivative, and X-ray luminosity of J1627 in the quasi-spin-equilibrium stage. To evolve to the current state of J1627, the initial mass-accretion rate of the fallback disk and the magnetic field of the NS are in the range of (1.1–30) × 1024 g s−1 and (2–5) × 1014 G, respectively. In the active lifetime of the fallback disk, it is impossible for J1839 to achieve the observed upper limit of the period derivative. Therefore, we propose that J1839 may be in the second ejector phase after the fallback disk becomes inactive. Those NSs with a magnetic field of (2–6) × 1014 G and a fallback disk with an initial mass-accretion rate of ∼1024–1026 g s−1 are possible progenitors of J1839. [ABSTRACT FROM AUTHOR]

Magnetized plasma columns and extended magnetic structures with both footpoints anchored to a surface layer are an important building block of astrophysical dissipation models. Current loops shining in X-rays during the growth of plasma instabilities are observed in the corona of the Sun and are expected to exist in highly magnetized neutron star magnetospheres and accretion disk coronae. For varying twist and system sizes, we investigate the stability of line-tied force-free flux tubes and the dissipation of twist energy during instabilities using linear analysis and time-dependent force-free electrodynamics simulations. Kink modes (m = 1) and efficient magnetic energy dissipation develop for plasma safety factors q ≲ 1, where q is the inverse of the number of magnetic field line windings per column length. Higher-order fluting modes (m > 1) can distort equilibrium flux tubes for q > 1 but induce significantly less dissipation. In our analysis, the characteristic pitch μ ˜ 0 of flux-tube field lines determines the growth rate ( ∝ μ ˜ 0 3 ) and minimum wavelength of the kink instability ( ∝ μ ˜ 0 − 1 ). We use these scalings to determine a minimum flux tube length for the growth of the kink instability for any given μ ˜ 0 . By drawing analogies to idealized magnetar magnetospheres with varying regimes of boundary shearing rates, we discuss the expected impact of the pitch-dependent growth rates for magnetospheric dissipation in magnetar conditions. [ABSTRACT FROM AUTHOR]

We reconsider the escape of high-brightness coherent emission of fast radio bursts (FRBs) from magnetars' magnetospheres, and conclude that there are numerous ways for the powerful FRB pulse to avoid non-linear absorption. Sufficiently strong surface magnetic fields, |$\ge 10{{\ \rm per\ cent}}$| of the quantum field, limit the waves' non-linearity to moderate values. For weaker fields, the electric field experienced by a particle is limited by a combined ponderomotive and parallel-adiabatic forward acceleration of charges by the incoming FRB pulse along the magnetic field lines newly opened during FRB/coronal mass ejection. As a result, particles surf the weaker front part of the pulse, experiencing low radiative losses, and are cleared from the magnetosphere for the bulk of the pulse to propagate. We also find that initial mildly relativistic radial plasma flow further reduces losses. [ABSTRACT FROM AUTHOR]

Magnetars are a type of pulsars powered by magnetic field energy. Part of the X‐ray luminosities of magnetars in quiescence have a thermal origin and can be fitted by a blackbody spectrum with the surface temperature, much higher than the typical values for rotation‐powered pulsars. The persistent thermal emissions and bursts of magnetars indicate the presence of some internal heat sources in their outer crusts. In this work, we have formulated the energy balance equation and applied it to investigate the thermal evolution in the magnetar crust, taking into account the heating mechanisms of Ohmic decay and electron capture processes. This model can explain the changes in the X‐ray luminosity of the magnetars. [ABSTRACT FROM AUTHOR]

At the high temperatures inside recently formed neutron stars (⁠|$T\gtrsim 5\times 10^{8}\, \text{K}$|⁠), the particles in their cores are in the 'strong-coupling' regime, in which collisional forces make them behave as a single, stably stratified, and thus non-barotropic fluid. In this regime, axially symmetric hydromagnetic quasi-equilibrium states are possible, which are only constrained to have a vanishing azimuthal Lorentz force. In these states, the particle species deviate from chemical (β) equilibrium, which tends to be restored by β decays (Urca reactions), inducing fluid motions that change the magnetic field configuration. If the stars remained hot for a sufficiently long time, this evolution would eventually lead to a chemical equilibrium state, in which the fluid is barotropic and the magnetic field, if axially symmetric, satisfies the non-linear Grad–Shafranov equation. Here, we present a numerical scheme that decouples the magnetic and thermal evolution, enabling to efficiently perform, for the first time, long-term magnetothermal simulations in this regime for different magnetic field strengths and geometries. Our results demonstrate that, even for magnetar-strength fields |$\gtrsim 10^{16} \, \mathrm{G}$|⁠ , the feedback from the magnetic evolution on the thermal evolution is negligible. Thus, as the core passively cools, the Urca reactions quickly become inefficient at restoring chemical equilibrium, so the magnetic field evolves very little, and the Grad–Shafranov state is not attained. Therefore, any substantial evolution of the core magnetic field must occur later, in the 'weak-coupling' regime (⁠|$T\lesssim 5\times 10^8 \, \mathrm{K}$|⁠), when Urca reactions are frozen and ambipolar diffusion becomes relevant. [ABSTRACT FROM AUTHOR]

SN 2019neq was a very fast evolving superluminous supernova. At a redshift z  = 0.1059, its peak absolute magnitude was −21.5 ± 0.2 mag in g band. In this work, we present data and analysis from an extensive spectrophotometric follow-up campaign using multiple observational facilities. Thanks to a nebular spectrum of SN 2019neq, we investigated some of the properties of the host galaxy at the location of SN 2019neq and found that its metallicity and specific star formation rate are in a good agreement with those usually measured for SLSNe-I hosts. We then discuss the plausibility of the magnetar and the circumstellar interaction scenarios to explain the observed light curves, and interpret a nebular spectrum of SN 2019neq using published sumo radiative-transfer models. The results of our analysis suggest that the spin-down radiation of a millisecond magnetar with a magnetic field |$B\simeq 6\times 10^{14}\, \mathrm{G}$| could boost the luminosity of SN 2019neq. [ABSTRACT FROM AUTHOR]

This study was focused on the investigation of a magnetic field penetrating from the core of a neutron star to its surface. The range of possible field configurations in the intermediate solid crust is less limited owing to the elastic force acting on the force balance. When the Lorentz force is excessively strong, the magnetoelastic equilibrium does not hold, and thus, the magnetic field becomes constrained. By numerically solving for the magnetoelastic equilibrium in a thin crust, the range of the magnetic field at the core–crust interface was determined, while assuming the exterior to be fixed as a dipole in vacuum. The results revealed that the toroidal component should be smaller than the poloidal component at the core–crust interface for the surface dipole, B 0 > 2.1 × 1014 G. Consequently, a strong toroidal field, for example, B ∼ 1016 G, as suggested by free precession of magnetars should be confined to a deep interior core and should be reduced to B ∼ 1014 G at the bottom of the crust. The findings of this study provide insights into the interior field structure of magnetars. Further investigations on more complicated geometries with higher multipoles and exterior magnetosphere are necessary. [ABSTRACT FROM AUTHOR]

We show that magnetar models for ultraluminous X-ray sources (ULXs) have serious internal inconsistencies. The magnetic fields required to increase the limiting luminosity for radiation pressure above the observed (assumed isotropic) luminosities are completely incompatible with the spin-up rates observed for pulsing ULXs. We note that at least one normal Be-star + neutron star system, with a standard (non-magnetar) field, is observed to become a ULX during a large outburst and return to its previous Be-star binary state afterwards. We note further that recent polarimetric observations of the well-studied binary Cyg X-3 reveal that it produces strong emission directed away from the observer, in line with theoretical predictions of its total accretion luminosity from evolutionary arguments. We conclude that the most likely explanation for ULX behaviour involves radiation beaming by accretion disc winds. A large fraction of X-ray binaries must pass through a ULX state in the course of their evolution. [ABSTRACT FROM AUTHOR]

We study numerically a combined gravitational and nonlinear magnetic lensing effect on electromagnetic flux. A magnetar with a dipole magnetic field and background gravitational field is considered to deflect the light rays which passed through its magnetosphere. We assume a square wave front with sides (1 5 0 × 1 5 0) × 1 0 3 m as a grid with the 1 0 3 m dynamic step. At the nodes of this grid, the rays enter perpendicularly into the cubic area, which covers the main magnetic lensing region with a magnetar at the center. On the basis of general relativity (GR) and nonlinear vacuum electrodynamics, the distribution of rays by the deflection angle in the combined field of the magnetar was obtained. On the basis of the analysis of the obtained data, it is possible to assert that the magnetic field distorts the result of gravitational lensing. Therefore, the magnetar is regarded as a gravitational-magnetic lensing object, wherein the magnetic field induces axial distortion within 1 0 − 6 ∘ . These results are expected to be detectable by modern instruments. [ABSTRACT FROM AUTHOR]

Some models of gamma-ray bursts (GRBs) invoke nascent millisecond magnetars as the central engine and address the X-ray afterglows with the interaction of magnetar magnetospheres with fallback discs. We study the evolution of fallback discs interacting with the millisecond magnetars. Initially, the accretion rate in the fallback disc is very high, well above the rate required for the Eddington limit. The inner parts of such a disc, even if it is cooling by the neutrino emission, get spherical due to the radiation pressure, which regulates the mass-accretion rate within the spherization radius. Such a disc can not penetrate the light cylinder radius for the typical magnetic fields, and the initial spin frequencies invoked for the magnetars. As a result of the autoregulation of the accretion flow, the fallback disc can not interact directly with the magnetar's magnetosphere within the first few days. This has implications for the fallback disc models of GRB afterglows since the accretion and propeller luminosities, in the presence of radiation pressure, are too low to address the typical luminosities of X-ray afterglows. [ABSTRACT FROM AUTHOR]

Off-centred dipole configurations have been suggested to explain different phenomena in neutron stars, such as natal kicks, irregularities in polarization of radio pulsars and properties of X-ray emission from millisecond pulsars. Here, for the first time, we model magnetothermal evolution of neutron stars with crust-confined magnetic fields and off-centred dipole moments. We find that the dipole shift decays with time if the initial configuration has no toroidal magnetic field. The decay time-scale is inversely proportional to magnetic field. The octupole moment decreases much faster than the quadrupole. Alternatively, if the initial condition includes strong dipolar toroidal magnetic field, the external poloidal magnetic field evolves from centred dipole to off-centred dipole. The surface thermal maps are very different for configurations with weak B  = 1013 G and strong B  = 1014 G magnetic fields. In the former case, the magnetic equator is cold while in the latter case, it is hot. We model light curves and spectra of our magnetothermal configurations. We found that in the case of cold equator, the pulsed fraction is small (below a few per cent in most cases) and spectra are well described with a single blackbody. Under the same conditions, models with stronger magnetic fields produce light curves with pulsed fraction of tens of per cent. Their spectra are significantly better described with two blackbodies. Overall, the magnetic field strength has a more significant effect on bulk thermal emission of neutron stars than does the field geometry. [ABSTRACT FROM AUTHOR]

The Tayler–Spruit dynamo is one of the most promising mechanisms proposed to explain angular momentum transport during stellar evolution. Its development in proto-neutron stars spun-up by supernova fallback has also been put forward as a scenario to explain the formation of very magnetized neutron stars called magnetars. Using three-dimensional direct numerical simulations, we model the proto-neutron star interior as a stably stratified spherical Couette flow with the outer sphere that rotates faster than the inner one. We report the existence of two subcritical dynamo branches driven by the Tayler instability. They differ by their equatorial symmetry (dipolar or hemispherical) and the magnetic field scaling, which is in agreement with different theoretical predictions (by Fuller and Spruit, respectively). The magnetic dipole of the dipolar branch is found to reach intensities compatible with observational constraints on magnetars. [ABSTRACT FROM AUTHOR]

We did 194 epochs of simultaneous 2.25/8.60 GHz observations of XTE J1810−197 in 926 days shortly following its reactivation in 2018 with Shanghai Tian Ma Radio Telescope (TMRT). Although its integrated profiles changed with both time and frequency during this period, they could be classified into 12 types according to phase areas of active radiation components. After MJD 59015, XTE J1810−197 turned from the normal emission state into the spiky emission state that was manifesting as a series of bright narrow sub-pulse bursts at both 2.25 and 8.60 GHz. Due to its variable integrated profiles and unsteady rotations, we got the spin frequency ν and spin-frequency derivatives ν ̇ with the piecewise fitting method. In addition, its long-term declining trend of ν was also obtained as ν ̇ = − 3.2 (1) × 10 − 13 s−2 with the linear fitting method based on our observations spanning a comparatively longer period. We found its flux densities went through three stages: sharp decrease, stabilization, and day-to-day fluctuations in our dual-frequency observations. Although the flux density showed different stages, XTE J1810−197 showed a relatively flat spectrum (α > –1) in most observations. Assuming an ideal dipole magnetic field as some previous research works, we obtained the emission heights of XTE J1810−197 were about 7.5(9) × 104 km and 2.38(7) × 104 km at 2.25 and 8.60 GHz, respectively. We also found that its emission heights would decrease rapidly with the degree of magnetic field twisting. [ABSTRACT FROM AUTHOR]

Recently, remarkable antiglitch and glitch accompanied by bright radio bursts of the Galactic magnetar SGR J1935+2154 were discovered. These two infrequent temporal coincidences between the glitch/antiglitch and the fast radio burst (FRB)-like bursts reveal their physical connection of them. Here, we propose that the antiglitch/glitch and FRB-like bursts can be well understood by an asteroid tidally captured by a magnetar. In this model, an asteroid is tidally captured and disrupted by a magnetar. Then, the disrupted asteroid will transfer the angular momentum to the magnetar producing a sudden change in the magnetar rotational frequency at the magnetosphere radius. If the orbital angular momentum of the asteroid is parallel (or antiparallel) to that of the spinning magnetar, a glitch (or antiglitch) will occur. Subsequently, the bound asteroid materials fall back to the pericentre and eventually are accreted to the surface of the magnetar. Massive fragments of the asteroid cross magnetic field lines and produce bright radio bursts through coherent curvature radiation. Our model can explain the sudden magnetar spin changes and FRB-like bursts in a unified way. [ABSTRACT FROM AUTHOR]

While the dipole magnetic field axis of neutron stars is usually postulated to cross the star's centre, it may be displaced from this location, as it has been recently indicated in the millisecond pulsar J0030+0451. Under these conditions, the electromagnetic rocket effect may be activated, where the magnetic field exerts a net force, accelerating the star. This post-natal kick mechanism relies on asymmetric electromagnetic radiation from an off-centre dipole and may be relevant to the high spatial velocities of pulsars |$\sim 10^{3}$|  km s−1. Here, we explore its impact in young pulsars associated with supernova remnants, and we compare the observational data on characteristic quantities, such as the braking index and proper motion, with results obtained from the rocket effect. Using a Markov Chain Monte Carlo analysis, we explore the required conditions, for the initial spin periods and the distance between the magnetic axis and the star's centre, so that the velocity kick due to the rocket effect approaches the present velocity. We find that the electromagnetic rocket effect can account for typical pulsar transverse velocities assuming an initial spin period of 3.8  |$\rm {ms}$| and a dipole field whose distance from the centre of the star is approximately 7  |$\rm {km}$|. We also explore the influence of the rocket effect on the braking index of a neutron star, and we find that for the sample studied this impact is minimal. Finally, we apply the rocket effect model on the pulsars J0030+0451 and J0538+2817, which are likely candidates for this mechanism. [ABSTRACT FROM AUTHOR]

No magnetotrophic organism on Earth is known to use magnetic fields as an energy source or the storage of information. However, a broad diversity of life forms is sensitive to magnetic fields and employs them for orientation and navigation, among other purposes. If the magnetic field strength were much larger, such as that on planets around neutron stars or magnetars, metabolic energy could be obtained from these magnetic fields in principle. Here, we introduce three hypothetical models of magnetotrophic organisms that obtain energy via the Lorentz force. Even if an organism uses magnetic fields only as an energy source, but otherwise is relying on biochemistry, this organism would be by definition a magnetotrophic form of life as we do not know it. [ABSTRACT FROM AUTHOR]

According to Einstein–Maxwell-dilaton theory, the dilaton field ψ can be produced by electromagnetic fields with non-zero Maxwell invariant. So electromagnetic wave propagating in an external electromagnetic field is a typical source of dilaton radiation. For study dilaton photoproduction in astrophysical conditions it's interesting to consider plane elliptically polarized electromagnetic wave propagating in the electromagnetic field of magnetic dipole m of pulsars and magnetars. The dilation field equation is solved in case | ψ | ≪ 1 . The angular distribution dilaton radiation is studied in every point of space. It's shown that spectral composition of dilatons is similar to spectral composition of plane electromagnetic wave. Amount of dilaton energy radiated in time and all directions is greatest in condition (B 1 2 - B 2 2) (m x 2 - m y 2) ≥ 0 , where B 1 and B 2 are electromagnetic wave amplitudes along the axes of polarization ellipse. This condition is valid for many neutron star systems. [ABSTRACT FROM AUTHOR]

Magnetars are believed to be neutron stars (NSs) with strong magnetic fields. X-ray flares and fast radio bursts (FRBs) have been observed from the magnetar (soft gamma-ray repeater, SGR J1935+2154). We propose that the phase transition of the NS can power the FRBs and SGRs. Based on the equation of state provided by the MIT bag model and the mean field approximation, we solve the Tolman–Oppenheimer–Volkoff equations to get the NS structure. With the spin-down of the NS, the hadronic shell gradually transfers to the quark shell. The gravitational potential energy released by one time of the phase transition can be achieved. The released energy, time interval between two successive phase transitions, and glitch are all consistent with the observations of the FRBs and the X-ray flares from SGR J1935 + 2154. We conclude that the phase transition of an NS is a plausible mechanism to power the SGRs as well as the repeating FRBs. [ABSTRACT FROM AUTHOR]

In this brief review, I summarize our basic knowledge about different types of isolated neutron stars. I discuss radio pulsars, central compact objects in supernova remnants, magnetars, nearby cooling neutron stars (also known as the magnificent seven), and sources of fast radio bursts. Several scenarios of magneto-rotational evolution are presented. Recent observational data, such as the discovery of long-period radio pulsars, require the non-trivial evolution of magnetic fields, the spin periods of neutron stars, or both. In some detail, I discuss different models of magnetic field decay and interactions of young neutron stars with fallback matter. [ABSTRACT FROM AUTHOR]

The "Triaxial Star", first proposed by S. Chandrasekhar in 1969, has not yet been detected. The recently detected Cosmic Baby, i.e., Swift J1818.0-1607 is the youngest magnetar observed so far. Its characteristic age is ∼300 years, with a superfast spin period ∼1.36 s and a strong surface dipole magnetic field ∼ 3 × 10 14 G . Considering the three facts in the interior of the magnetar core: i) the ambipolar diffusion, ii) negligible field decay as long as the core temperature is a few times 10 8 K and iii) the strong coupling between internal magnetic field decay and cooling in the early phase we estimate the ellipticity (ϵ ) and the core magnetic field ( B internal ) of this newly born magnetar are ∼ 9 × 10 − 3 and 8.9424 × 10 17 G , respectively. Based on our estimated result we suggest Swift J1818.0-1607 is a triaxial magnetar, i.e., simply a Triaxial Star. We discuss the significance of our result and encourage the GW community to search the triaxial stars through electromagnetic counterparts during their observation. [ABSTRACT FROM AUTHOR]

The recent observations of the anomalous X-ray pulsars 4U 0142+61 and 1RXS J170849.0-400910 by the Imaging X-ray Polarimetry Explorer (IXPE) opened up a new avenue to study magnetars, neutron stars endowed with superstrong magnetic fields (B & 1014 G). The detected polarized X-rays from 4U 0142+61 exhibit a 90° linear polarization swing from low photon energies (E. 4 keV) to high energies (E & 5:5 keV). We show that this swing can be explained by photon polarization mode conversion at the vacuum resonance in the magnetar atmosphere; the resonance arises from the combined effects of plasma-induced birefringence and Quantum electrodynamics (QED)-induced vacuum birefringence in strong magnetic fields. This explanation suggests that the atmosphere of 4U 0142 is composed of partially ionized heavy elements and that the surface magnetic field is comparable to or less than 1014 G, consistent with the dipole field inferred from the measured spindown. It also implies that the spin axis of 4U 0142+61 is aligned with its velocity direction. The polarized X-rays from 1RXS J170849.0-400910 do not show such 90° swing, consistent with magnetar atmospheric emission with B & 5 x 1014 G. [ABSTRACT FROM AUTHOR]

The radio pulsar GLEAM-X J162759.5–523504.3 has an extremely long spin period (⁠|$P = 1091.17\, \mbox{s}$|⁠), and yet seemingly continues to spin-down rapidly (⁠|$\dot{P} < 1.2 \times 10^{-9}\, \mbox{ss}^{-1}$|⁠). The magnetic field strength that is implied, if the source is a neutron star undergoing magnetic dipole braking, could exceed |$10^{16}\, \mbox{G}$|⁠. This object may therefore be the most magnetized neutron star observed to date. In this paper, a critical analysis of a magnetar interpretation for the source is provided. (i) A minimum polar magnetic field strength of |$B \sim 5 \times 10^{15}\, \mbox{G}$| appears to be necessary for the star to activate as a radio pulsar, based on conventional 'death valley' assumptions. (ii) Back-extrapolation from magnetic braking and Hall–plastic–Ohm decay suggests that a large angularize momentum reservoir was available at birth to support intense field amplification. (iii) The observational absence of X-rays constrains the star's field strength and age, as the competition between heating from field decay and Urca cooling implies a surface luminosity as a function of time. If the object is an isolated, young (⁠|$\sim 10\, \mbox{kyr}$|⁠) magnetar with a present-day field strength of |$B \gtrsim 10^{16}\, \mbox{G}$|⁠ , the upper limit (⁠|$\approx 10^{30}\, \mbox{erg s}^{-1}$|⁠) set on its thermal luminosity suggests it is cooling via a direct Urca mechanism. [ABSTRACT FROM AUTHOR]

Fast radio bursts (FRBs) were discovered only in 2007. However, the number of known events and sources of repeating bursts grows very rapidly. In the near future, the number of events will be ≳104 and the number of repeaters ≳100. Presently, there is a consensus that most of the sources of FRBs might be neutron stars (NSs) with large magnetic fields. These objects might have different origin as suggested by studies of their host galaxies which represent a very diverse sample: from regions of very active star formation to old globular clusters. Thus, in the following decade we expect to have a very large sample of events directly related to extragalactic magnetars of different origin. This might open new possibilities to probe various aspects of NS physics. In the review we briefly discuss the main directions of such future studies and summarize our present knowledge about FRBs and their sources. [ABSTRACT FROM AUTHOR]

Magnetar outbursts are powered by an intense magnetic field. The phenomenon has recently drawn significant attention because of a connection to some fast radio bursts that has been reported. Understanding magnetar outbursts may provide the key to mysterious transient events. The elastic deformation of the solid crust due to magnetic field evolution accumulates over a secular timescale. Eventually, the crust fractures or responds plastically beyond a particular threshold. Determination of the critical limit is required to obtain the shear strain tensor in response to magnetic stress. In some studies, the tensor was substituted with an approximate expression determined algebraically from the magnetic stress. This study evaluated the validity of the approximation by comparing it with the strain tensor obtained through appropriate calculations. The differential equations for the elastic deformation driven by the magnetic field were solved. The results indicated that the approximation did not represent the correct strain tensor value, in both magnitude and spatial profile. Previous evolutionary calculations based on spurious criteria are likely to overestimate the magnitude of the strain tensor, and crustal failure occurs on a shorter timescale. Therefore, revisiting evolutionary calculations using the correct approach is necessary. This study is essential for developing the dynamics of crustal fractures and the magnetic field evolution in a magnetar.

Recently, two ultralong-period radio transients, GLEAM-X J162759.5-523504.3 (J1627) and GPM J1839-10 (J1839), were discovered with spin periods longer than 1000 s. The origin of these two ultralong-period radio transients is intriguing in understanding the spin evolution of neutron stars (NSs). In this work, we examine whether the interaction between strong magnetized NSs and fallback disks can spin NSs down to the observed ultralong period. Our simulations found that the magnetar + fallback disk model can account for the observed period, period derivative, and X-ray luminosity of J1627 in the quasi-spin-equilibrium stage. To evolve to the current state of J1627, the initial mass-accretion rate of the fallback disk and the magnetic field of the NS are in the range of (1.1–30) × 10 ^24 g s ^−1 and (2–5) × 10 ^14 G, respectively. In the active lifetime of the fallback disk, it is impossible for J1839 to achieve the observed upper limit of the period derivative. Therefore, we propose that J1839 may be in the second ejector phase after the fallback disk becomes inactive. Those NSs with a magnetic field of (2–6) × 10 ^14 G and a fallback disk with an initial mass-accretion rate of ∼10 ^24 –10 ^26 g s ^−1 are possible progenitors of J1839.

Magnetized plasma columns and extended magnetic structures with both footpoints anchored to a surface layer are an important building block of astrophysical dissipation models. Current loops shining in X-rays during the growth of plasma instabilities are observed in the corona of the Sun and are expected to exist in highly magnetized neutron star magnetospheres and accretion disk coronae. For varying twist and system sizes, we investigate the stability of line-tied force-free flux tubes and the dissipation of twist energy during instabilities using linear analysis and time-dependent force-free electrodynamics simulations. Kink modes ( m = 1) and efficient magnetic energy dissipation develop for plasma safety factors q ≲ 1, where q is the inverse of the number of magnetic field line windings per column length. Higher-order fluting modes ( m > 1) can distort equilibrium flux tubes for q > 1 but induce significantly less dissipation. In our analysis, the characteristic pitch ${\tilde{\mu }}_{0}$ of flux-tube field lines determines the growth rate ( $\propto {\tilde{\mu }}_{0}^{3}$ ) and minimum wavelength of the kink instability ( $\propto {\tilde{\mu }}_{0}^{-1}$ ). We use these scalings to determine a minimum flux tube length for the growth of the kink instability for any given ${\tilde{\mu }}_{0}$ . By drawing analogies to idealized magnetar magnetospheres with varying regimes of boundary shearing rates, we discuss the expected impact of the pitch-dependent growth rates for magnetospheric dissipation in magnetar conditions.

Magnetars exhibit a variety of transient high-energy phenomena in the form of bursts, outbursts, and giant flares. It is a common belief that these events originate in the sudden release of magnetic energy due to the rearrangement of a twisted magnetic field. We present global models of a 3D force-free (FF) non-linear twisted magnetar magnetosphere. We solve the FF equations following the Grad–Rubin approach in a compactified spherical domain. Appropriate boundary conditions are imposed at the surface of the star for the current distribution and the magnetic field. Our implementation is tested by reproducing various known analytical as well as axisymmetric numerical results. We then proceed to study general 3D models with non-axisymmetric current distributions, such as fields with localized twists that resemble hotspots at the surface of the star, and we examine characteristic quantities such as energy, helicity, and twist. Finally, we discuss implications on the available energy budget, the surface temperature, and the diffusion time-scale, which can be associated with observations. [ABSTRACT FROM AUTHOR]

We investigate the impact of strong initial magnetic fields in core-collapse supernovae of non-rotating progenitors by simulating the collapse and explosion of a |$16.9\, \mathrm{M}_\odot$| star for a strong- and weak-field case assuming a twisted-torus field with initial central field strengths of |${\approx }10^{12}$| and |${\approx }10^{6}\, \mathrm{G}$|⁠. The strong-field model has been set up with a view to the fossil-field scenario for magnetar formation and emulates a pre-collapse field configuration that may occur in massive stars formed by a merger. This model undergoes shock revival already |$100\, \mathrm{ms}$| after bounce and reaches an explosion energy of |$9.3\times 10^{50}\, \mathrm{erg}$| at |$310\, \mathrm{ms}$|⁠ , in contrast to a more delayed and less energetic explosion in the weak-field model. The strong magnetic fields help trigger a neutrino-driven explosion early on, which results in a rapid rise and saturation of the explosion energy. Dynamically, the strong initial field leads to a fast build-up of magnetic fields in the gain region to 40 per cent of kinetic equipartition and also creates sizable pre-shock ram pressure perturbations that are known to be conducive to asymmetric shock expansion. For the strong-field model, we find an extrapolated neutron star kick of |${\approx }350\, \mathrm{km}\, \mathrm{s}^{-1}$|⁠ , a spin period of |${\approx }70\, \mathrm{ms}$|⁠ , and no spin-kick alignment. The dipole field strength of the proto-neutron star is |$2\times 10^{14}\, \mathrm{G}$| by the end of the simulation with a declining trend. Surprisingly, the surface dipole field in the weak-field model is stronger, which argues against a straightforward connection between pre-collapse fields and the birth magnetic fields of neutron stars. [ABSTRACT FROM AUTHOR]

The luminosity of the Soft Gamma Repeater flares significantly exceeds the Eddington luminosity. This is because they emit mainly in the E mode, for which the radiative cross-sections are strongly suppressed. The energy is released in the magnetosphere forming a magnetically trapped pair fireball, and the surface of the star is illuminated by the powerful radiation from the fireball. We study the ablation of the matter from the surface by this radiation. The E-mode photons are scattered within the surface layer, partly being converted into O-photons, whose scattering cross-section is of the order of the Thomson cross-section. The high radiation pressure of the O-mode radiation expels the plasma upwards. The uplifted matter forms a thick baryon sheath around the fireball. If an illuminated fraction of the star's surface includes the polar cap, a heavy, mildly relativistic baryonic wind is formed. [ABSTRACT FROM AUTHOR]

The amplification of magnetic fields plays an important role in explaining numerous astrophysical phenomena associated with binary neutron star mergers, such as mass ejection and the powering of short gamma-ray bursts. Magnetic fields in isolated neutron stars are often assumed to be confined to a small region near the stellar surface, while they are normally taken to fill the whole star in numerical modeling of mergers. By performing high-resolution, global, and high-order general-relativistic magnetohydrodynamic simulations, we investigate the impact of a purely crustal magnetic field and contrast it with the standard configuration consisting of a dipolar magnetic field with the same magnetic energy but filling the whole star. While the crust configurations are very effective in generating strong magnetic fields during the Kelvin–Helmholtz-instability stage, they fail to achieve the same level of magnetic-field amplification of the full-star configurations. This is due to the lack of magnetized material in the neutron-star interiors to be used for further turbulent amplification and to the surface losses of highly magnetized matter in the crust configurations. Hence, the final magnetic energies in the two configurations differ by more than 1 order of magnitude. We briefly discuss the impact of these results on astrophysical observables and how they can be employed to deduce the magnetic topology in merging binaries.

Magnetically confined mountains on accreting neutron stars are candidates for producing continuous gravitational waves. We formulate a magnetically confined mountain on a neutron star with strong multipole magnetic fields and obtain some sequences of numerical solutions. We find that the mass ellipticity of the mountain increases by one order of magnitude if the neutron star has strong multipole magnetic fields. As matter accretes on to the magnetic pole, the size of the mountain increases and the magnetic fields are buried. If the neutron star has a dipole magnetic field, the dipole magnetic field is buried and transformed into multipole components. By contrast, if the neutron star has both dipole and strong multipole magnetic fields, the multipole magnetic fields are buried and transformed into a negative dipole component. We also calculate magnetically confined mountains with toroidal magnetic fields and find that the ellipticity becomes slightly smaller when the mountain has toroidal magnetic fields. If the multipole magnetic fields are buried, they sustain the intense toroidal magnetic field near the stellar surface, and the ratio of the toroidal magnetic field to the poloidal magnetic field is close to 100. The hidden strong toroidal magnetic fields are sustained by the buried multipole magnetic fields. [ABSTRACT FROM AUTHOR]

Magnetars are neutron stars with ultrastrong magnetic fields, which can be observed in x-rays. Polarization measurements could provide information on their magnetic fields and surface properties. We observed polarized x-rays from the magnetar 4U 0142+61 using the Imaging X-ray Polarimetry Explorer and found a linear polarization degree of 13.5 ± 0.8% averaged over the 2– to 8–kilo–electron volt band. The polarization changes with energy: The degree is 15.0 ± 1.0% at 2 to 4 kilo–electron volts, drops below the instrumental sensitivity ~4 to 5 kilo–electron volts, and rises to 35.2 ± 7.1% at 5.5 to 8 kilo–electron volts. The polarization angle also changes by 90° at ~4 to 5 kilo–electron volts. These results are consistent with a model in which thermal radiation from the magnetar surface is reprocessed by scattering off charged particles in the magnetosphere. [ABSTRACT FROM AUTHOR]

This study investigates elastic deformation driven by the Hall drift in a magnetized neutron-star crust. Although the dynamic equilibrium initially holds without elastic displacement, the magnetic-field evolution changes the Lorentz force over a secular timescale, which inevitably causes the elastic deformation to settle in a new force balance. Accordingly, elastic energy is accumulated, and the crust is eventually fractured beyond a particular threshold. We assume that the magnetic field is axially symmetric, and we explicitly calculate the breakup time, maximum elastic energy stored in the crust, and spatial shearâ€"stress distribution. For the barotropic equilibrium of a poloidal dipole field expelled from the interior core without a toroidal field, the breakup time corresponds to a few years for the magnetars with a magnetic-field strength of ∼1015 G; however, it exceeds 1 Myr for normal radio pulsars. The elastic energy stored in the crust before the fracture ranges from 1041 to 1045 erg, depending on the spatial-energy distribution. Generally, a large amount of energy is deposited in a deep crust. The energy released at a fracture is typically ∼1041 erg when the rearrangement of elastic displacements occurs only in the fragile shallow crust. The amount of energy is comparable to the outburst energy on the magnetars. [ABSTRACT FROM AUTHOR]

Recent observations of coherent radiation from the Crab pulsar suggest the emission is driven by an ultrarelativistic (γ ∼ 104), cold plasma flow. A relativistically expanding plasma shell can compress the ambient magnetic field, like a moving mirror, and thus produce coherent radiation whose wavelength is shorter than that of the ambient medium by γ2. This mechanism has been previously studied in the context of radio loud supernova explosions. In this work, we propose that a similar mechanism drives the coherent emission in fast radio bursts. The high Lorenz factors dramatically lower the implied energy and magnetic field requirements, allowing the spin-down energy of regular (or even recycled), fast spinning pulsars, rather than slow spinning magnetars, to explain FRBs. We show that this model can explain the frequency and the time evolution of observed FRBs, as well as their duration, energetics, and absence of panchromatic counterparts. We also predict that the peak frequency of subpulses decline with observation time as |$\omega _{\rm obs} \propto t_{\rm obs}^{-1/2}$|⁠. Unfortunately, with current capabilities it is not possible to constrain the shape of the curve ωobs(t obs). Finally, we find that a variation of this model can explain weaker radio transients, such as the one observed from a galactic magnetar. In this variant, the shock wave produces low-frequency photons that are then Compton scattered to the GHz range. [ABSTRACT FROM AUTHOR]

At least some fast radio bursts (FRBs) are produced by magnetars. Even though mounting observational evidence points towards a magnetospheric origin of FRB emission, the question of the location for FRB generation continues to be debated. One argument suggested against the magnetospheric origin of bright FRBs is that the radio waves associated with an FRB may lose most of their energy before escaping the magnetosphere because the cross-section for e ± to scatter large-amplitude electromagnetic waves in the presence of a strong magnetic field is much larger than the Thompson cross-section. We have investigated this suggestion and find that FRB radiation travelling through the open field line region of a magnetar's magnetosphere does not suffer much loss due to two previously ignored factors. First, the plasma in the outer magnetosphere (⁠|$r \gtrsim 10^9$| cm), where the losses are potentially most severe, is likely to be flowing outwards at a high Lorentz factor γ p ≥ 103. Secondly, the angle between the wave vector and the magnetic field vector, θ B , in the outer magnetosphere is likely of the order of 0.1 radian or smaller due in part to the intense FRB pulse that tilts open magnetic field lines so that they get aligned with the pulse propagation direction. Both these effects reduce the interaction between the FRB pulse and the plasma substantially. We find that a bright FRB with an isotropic luminosity |$L_{\rm frb} \gtrsim 10^{42} \, {\rm erg \ s^{-1}}$| can escape the magnetosphere unscathed for a large section of the γ p − θ B parameter space, and therefore conclude that the generation of FRBs in magnetar magnetosphere passes this test. [ABSTRACT FROM AUTHOR]

The defining trait of magnetars, the most strongly magnetized neutron stars (NSs), is their transient activity in the X/ Îł -bands. In particular, many of them undergo phases of enhanced emission, the so-called outbursts, during which the luminosity rises by a factor ∼10â€"1000 in a few hours to then decay over months/years. Outbursts often exhibit a thermal spectrum, associated with the appearance of hotter regions on the surface of the star, which subsequently change in shape and cool down. Here we simulate the unfolding of a sudden, localized heat injection in the external crust of an NS with a 3D magnetothermal evolution code, finding that this can reproduce the main features of magnetar outbursts. A full 3D treatment allows us to study for the first time the inherently asymmetric hot spots that appear on the surface of the star as the result of the injection and to follow the evolution of their temperature and shape. We investigate the effects produced by different physical conditions in the heated region, highlighting in particular how the geometry of the magnetic field plays a key role in determining the properties of the event. [ABSTRACT FROM AUTHOR]

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 σ B = 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. [ABSTRACT FROM AUTHOR]

NGC 300 ULX1 is a pulsating ultraluminous X-ray source (PULX) with the longest spin period of |$P\simeq 31.6\, \rm s$| and a high spin-up rate of |$\dot{P}\simeq -5.56\times 10^{-7}\, \rm s\, s^{-1}$| that is ever seen in the confirmed PULXs. In this paper, the inferred magnetic field of NGC 300 ULX1 is |$\sim 3.0\times 10^{14}\, \rm G$| using the recent observed parameters after its first detection of pulsations. According to the evolved simulation of the magnetic field and the spin period, it will become a recycled pulsar or a millisecond pulsar under the conditions of the companion mass and the accretion rate limitation. We suggest that NGC 300 ULX1 is an accreting magnetar accounting for its super Eddington luminosity. We also propose that there might be other accreting magnetars in the confirmed PULXs. Such PULXs will be helpful for understanding the magnetar evolution and the millisecond pulsar formation whose magnetic field is stronger than |$\sim 10^{9}\, \rm G$|⁠. [ABSTRACT FROM AUTHOR]

SN 2018hti was a very nearby (z = 0.0614) superluminous supernova with an exceedingly bright absolute magnitude of −21.7 mag in r band at maximum. The densely sampled pre-maximum light curves of SN 2018hti show a slow luminosity evolution and constrain the rise time to ∼50 rest-frame d. We fitted synthetic light curves to the photometry to infer the physical parameters of the explosion of SN 2018hti for both the magnetar and the CSM-interaction scenarios. We conclude that one of two mechanisms could be powering the luminosity of SN 2018hti; interaction with ∼10 M⊙ of circumstellar material or a magnetar with a magnetic field of B p∼ 1.3 × 1013 G, and initial period of P spin∼ 1.8 ms. From the nebular spectrum modelling we infer that SN 2018hti likely results from the explosion of a |${\sim}40\, \mathrm{M}_\odot$| progenitor star. [ABSTRACT FROM AUTHOR]

The recent detection of a fast radio burst (FRB) from a Galactic magnetar secured the fact that neutron stars (NSs) with superstrong magnetic fields are capable of producing these extremely bright coherent radio bursts. One of the leading mechanisms to explain the origin of such coherent radio emission is the curvature radiation process within the dipolar magnetic field structure. It has, however, already been demonstrated that magnetars likely have a more complex magnetic field topology. Here, we critically investigate curvature radio emission in the presence of inclined dipolar and quadrupolar ('quadrudipolar') magnetic fields and show that such field structures differ in their angular characteristics from a purely dipolar case. We analytically show that the shape of open field lines can be modified significantly depending on both the ratio of quadrupole to dipole field strength and their inclination angle at the NS surface. This creates multiple points along each magnetic field line that coincide with the observer's line of sight, and may explain the complex spectral and temporal structure of the observed FRBs. We also find that in quadrudipole, the radio beam can take a wider angular range and the beamwidth can be wider than that in pure dipole. This may explain why the pulse width of the transient radio pulsation from magnetars is as large as that of ordinary radio pulsars. [ABSTRACT FROM AUTHOR]

We study the deflection of light by a magnetic dipole field in the generalized Born–Infeld electrodynamics. Using the effective index of refraction and the trajectory equation based on geometric optics, we compute the weak bending angle of light passing on the equator of the magnetic dipole. In the limit where the classical Born–Infeld parameter is infinite, the bending angle agree with the one computed from the Euler–Heisenberg Lagrangian. We also compute the bending angle using the geodesic equation of the effective metric induced by a massive object with magnetic dipole. In the massless limit the bending angle agrees with the computation using the trajectory equation. We apply the result to magnetars to estimate the order of magnitude for the bending angle. [ABSTRACT FROM AUTHOR]

The LIGOâ€"Virgoâ€"KAGRA Collaboration recently detected gravitational waves (GWs) from the merger of black holeâ€"neutron star (BHNS) binary systems GW200105 and GW200115. No coincident electromagnetic (EM) counterparts were detected. While the mass ratio and BH spin in both systems were not sufficient to tidally disrupt the NS outside the BH event horizon, other, magnetospheric mechanisms for EM emission exist in this regime and depend sensitively on the NS magnetic field strength. Combining GW measurements with EM flux upper limits, we place upper limits on the NS surface magnetic field strength above which magnetospheric emission models would have generated an observable EM counterpart. We consider fireball models powered by the black hole battery mechanism, where energy is output in gamma rays over ≲1 s. Consistency with no detection by Fermi-GBM or INTEGRAL SPI-ACS constrains the NS surface magnetic field to ≲1015 G. Hence, joint GW detection and EM upper limits rule out the theoretical possibility that the NSs in GW200105 and GW200115, and the putative NS in GW190814, retain dipolar magnetic fields ≳1015 G until merger. They also rule out formation scenarios where strongly magnetized magnetars quickly merge with BHs. We alternatively rule out operation of the BH-battery-powered fireball mechanism in these systems. This is the first multimessenger constraint on NS magnetic fields in BHNS systems and a novel approach to probe fields at this point in NS evolution. This demonstrates the constraining power that multimessenger analyses of BHNS mergers have on BHNS formation scenarios, NS magnetic field evolution, and the physics of BHNS magnetospheric interactions. [ABSTRACT FROM AUTHOR]

In order to address the generation of neutron star magnetic fields, with particular focus on the dichotomy between magnetars and radio pulsars, we consider the properties of dynamos as inferred from other astrophysical systems. With sufficiently low (modified) Rossby number, convective dynamos are known to produce dipole-dominated fields whose strength scales with convective flux, and we argue that these expectations should apply to the convective protoneutron stars (PNSs) at the centers of core-collapse supernovae. We analyze a suite of three-dimensional simulations of core collapse, featuring a realistic equation of state and full neutrino transport, in this context. All our progenitor models, ranging from 9 M⊙ to 25 M⊙, including one with initial rotation, have sufficiently vigorous PNS convection to generate dipole fields of order ∼1015 Gauss, if the modified Rossby number resides in the critical range. Thus, the magnetar/radio pulsar dichotomy may arise naturally in part from the distribution of core rotation rates in massive stars. [ABSTRACT FROM AUTHOR]