Magnetar Research Articles

Extragalactic magnetar giant flare GRB 231115A: Insights from Fermi /GBM observations

Magnetar giant flares (MGFs) are the extremely short, energetic transients originating from highly magnetized neutron stars. When observed in nearby galaxies, these rare events are nearly indistinguishable from cosmological short gamma-ray bursts. We present the analysis of GRB,231115A, a candidate extragalactic MGF observed by and localized by to the starburst galaxy M82. This burst exhibits distinctive temporal and spectral characteristics, including a short duration and a high peak energy, consistent with known MGFs. Time-resolved analysis reveals rapid spectral evolution and a clear correlation between luminosity and spectral hardness, providing robust evidence of relativistic outflows. Archival Chandra data identified point sources within the GRB,231115A localization consistent with the theoretical maximum persistent emission luminosity, though no definitive counterpart was found. Simulations indicate that any transient emission associated with GRB,231115A would require energies exceeding those of typical magnetar bursts to be detectable by current instruments. While the tail of a MGF originating from outside of the Milky Way and its satellite galaxies has never been detected, analysis suggests that such emission could be observable at M82’s distance with instruments like Swift /XRT or NICER, though no tail was identified for this event. These findings underscore the need for improved follow-up strategies and technological advancements to enhance MGF detection and characterization.

Charged particles in dipole magnetosphere of neutron stars: epicyclic oscillations in and off-equatorial plane

Abstract We study the motion of charged test particles around a magnetized neutron star described by the Schwarzschild gravitational field of mass M and a dipole magnetic field characterized by parameter b, representing the ratio of electromagnetic to gravitational forces. The neutron star’s radius is assumed at $$R=3M$$ R = 3 M . Circular orbits “in” and “off” the equatorial plane, determined by the dipole field’s symmetry plane, are analyzed based on background and particle parameters; their stability against radial and latitudinal perturbations is established. The existence of chaotic charged particle motion in belts around off-equatorial orbits, influenced by sufficiently strong repulsive magnetic force, is demonstrated. The belts’ distance from the neutron star varies with parameter b for different charged particles. Frequencies of epicyclic oscillatory motion related to “in” and “off” equatorial circular orbits, alongside the orbital frequency, are determined. The magnetically modified geodesic model is applied to fit observational data from twin-peak, high-frequency quasi-periodic oscillations in binary systems containing neutron stars. Rough fitting to the data for circular orbits for particles under magnetic attraction (repulsion) is shown. The possible fittings imply strong limits on the magnetic parameter, $$b \sim 0.01$$ b ∼ 0.01 ( $$b \sim -10$$ b ∼ - 10 ) for magnetic attraction (repulsion), suggesting minor influence of electromagnetic forces and test particles with small specific charges like dust or plasmoids in strong magnetic fields around neutron stars.

Non-Keplerian Charged Accretion Disk Orbiting a Black Hole Pulsar

Recent studies have focused on how spinning black holes (BHs) within a binary system containing a strongly magnetized neutron star, then immersed in external magnetic fields, can acquire charge through mechanisms like the Wald process and how this charge could power pulsar-like electromagnetic radiation. Those objects called “Black hole pulsar” mimic the behaviour of a traditional pulsar, and they can generate electromagnetic fields, such as magnetic dipoles. Charged particles within an accretion disk around the black hole would then be influenced not only by the gravitational forces but also by electromagnetic forces, leading to different geometries and dynamics. In this context, we focus here on the interplay of the magnetic dipole and the accretion disk. We construct the equilibrium structures of non-conducting charged perfect fluids orbiting Kerr black holes under the influence of a dipole magnetic field aligned with the rotation axis of the BH. The dynamics of the accretion disk in such a system are shaped by a complex interplay between the non-uniform, non-Keplerian angular momentum distribution, the black hole’s induced magnetic dipole, and the fluid’s charge. We show how these factors jointly influence key properties of the disk, such as its geometry, aspect ratio, size, and rest mass density.

Conversion of emitted axionic dark matter to photons for non-rotating magnetized neutron stars

Conversion of emitted axionic dark matter to photons for non-rotating magnetized neutron stars

Full 3D nonlinear dynamics of charged and magnetized boson stars

Full 3D nonlinear dynamics of charged and magnetized boson stars

Modeling the Emission and Polarization Properties of Pulsating Ultraluminous X‐Ray Sources

ABSTRACTPulsating Ultraluminous X‐ray Sources (PULXs) are a class of extragalactic sources with high X‐ray luminosity, in excess of erg , and showing pulsations that associate them with neutron stars accreting at a super‐Eddington rate. A simplified model is presented, which describes the thermal emission from an accreting, highly magnetized neutron star and includes the contributions from an accretion disk and an accretion envelope surrounding the star magnetosphere. Through numerical calculations, we determine the flux, pulsed fractions, polarization degree, and polarization angle considering various viewing geometries. The model is confronted with the XMM‐Newton spectra of M51 ULX‐7, and the best fitting viewing geometries are estimated. A measurement of the polarization observables, which will be available with future facilities, along with spectroscopic data obtained with XMM‐Newton, will provide considerable additional information on these sources.

Disk-locking Regulates Stellar Rotation in Young Clusters: Insights from NGC 2264

Abstract Many young clusters possess extended main sequences, a phenomenon commonly ascribed to stellar rotation. However, the mechanism behind their very wide stellar rotation distributions remains unclear. A proposed explanation is that magnetic star–disk interaction can regulate stellar rotation, i.e., protostars with longer disk lifetimes will eventually evolve into slow rotators, and vice versa. To examine this hypothesis, we took the star-forming region NGC 2264, as a test bed. We have studied its high-mass pre-main-sequence and zero-age main-sequence (ZAMS) stars. We find that, on average, diskless pre-main-sequence stars rotate faster than their disk-bearing counterparts. The stellar rotation distribution of the ZAMS stars is similar to evolved young clusters. We conclude that disk-locking may play a crucial role in the rotational velocity distribution of intermediate-mass early-type stars. We suggest that the observed wide stellar rotation distributions in many young clusters can occur in their early stages.

Unveiling the Magnetized Nature of X‐Ray Binaries: Cyclotron Line Insights Title

ABSTRACTStudying the variations of measured cyclotron lines plays a crucial role in gaining insights into the physical processes of accretion in magnetized neutron stars. Our research focuses on the formation and distribution of magnetic fields in various high‐mass x‐ray binaries (HMXBs). Comparing these sources reveals valuable information about their origin and evolutionary history. It is worth noting that the presence of varying cyclotron lines can be attributed to the influence of accretion dynamics, which provides valuable information about the characteristics of the magnetic field. In addition, by visualizing data, we employ the Kernel Density Estimation method, to provide a robust framework for understanding the distribution of magnetic fields. We observed clear patterns of clustering in the energy range of (10–35) keV, which corresponds to magnetic fields of around G. This clustering indicates a shared magnetic field characteristics across these systems, suggesting a possible common origin or similar environmental and accretion condi tions. Finally, our research investigates the behavior of cyclotron lines in HMXBs, illuminating the accretion process and magnetic field properties to better understand their role as indicators of dynamical evolution.

What we can learn about Mars from the magnetism of returned samples

The Red Planet is a magnetic planet. The Martian crust contains strong magnetization from a core dynamo that likely was active during the Noachian period when the surface may have been habitable. The evolution of the dynamo may have played a central role in the evolution of the early atmosphere and the planet's transition to the current cold and dry state. However, the nature and history of the dynamo and crustal magnetization are poorly understood given the lack of well-preserved, oriented, ancient samples with geologic context available for laboratory study. Here, we describe how magnetic measurements of returned samples could transform our understanding of six key unknowns about Mars' planetary evolution and habitability. Such measurements could i) determine the history of the Martian dynamo field's intensity; ii) determine the history of the Martian dynamo field's direction; iii) test the hypothesis that Mars experienced plate tectonics or true polar wander; iv) constrain the thermal and aqueous alteration history of the samples; v) identify sources of Martian crustal magnetization and vi) characterize sedimentary and magmatic processes on Mars. We discuss how these goals can be achieved using future laboratory analyses of samples acquired by the Perseverance rover.

Pulsating ultraluminous X-ray sources: Modeling the thermal emission and polarization properties

Context. Ultraluminous X-ray sources (ULXs) are enigmatic sources first discovered in the 1980s in external galaxies. They are characterized by their extraordinarily high X-ray luminosity, which often exceeds 1040 erg s−1. Aims. Our study aims to obtain more information about pulsating ULXs (PULXs), first of all, their viewing geometry, since it affects almost all the observables, such as the flux, the pulsed fraction, the polarization degree (PD), and polarization angle (PA). Methods. We present a simplified model, which primarily describes the thermal emission from an accreting, highly magnetized neutron star, simulating the contributions of an accretion disk and an accretion envelope surrounding the star magnetosphere, both described by a multicolor blackbody. Numerical calculations are used to determine the flux, PD, and PA of the emitted radiation, considering various viewing geometries. The model predictions are then compared to the observed spectra of two PULXs, M51 ULX-7 and NGC 7793 P13. Results. We identified the best fitting geometries for these sources, obtaining values of the pulsed fraction and the temperature at the inner radius of the disk compatible with those obtained from previous works. We also found that measuring the polarization observables can give considerable additional information on the source.

Strong-field QED effects on polarization states in dipole and quadrudipole pulsar emissions

Highly magnetized neutron stars have quantum refraction effects on pulsar emission due to the non-linearity of the quantum electrodynamics (QED) action. In this paper, we investigate the evolution of the polarization states of pulsar emission under the quantum refraction effects, combined with the dependence on the emission frequency, for dipole and quadrudipole pulsar models; we solve a system of evolution equations of the Stokes vector, where the birefringent vector, in which such effects are encoded, acts on the Stokes vector. At a fixed emission frequency, depending on the magnitude of the birefringent vector, dominated mostly by the magnetic field strength, the evolution of the Stokes vector largely exhibits three different patterns: (i) monotonic, or (ii) half-oscillatory, or (iii) highly oscillatory behaviors. These features are understood and confirmed by means of approximate analytical solutions to the evolution equations. Also, the evolution patterns are shown to differ between dipole and quadrudipole pulsar models, depending on the magnetic field strength.

Accretion Onto Weakly Magnetized Neutron Stars: Polarization Theory and Its Application to X‐Ray Burster GX 13+1

ABSTRACTObservations show that the x‐ray emission of the accreting weakly magnetized neutron stars (WMNSs) is polarized. In this article, we summarize the analytical models for the polarized emission of various components of the WMNSs. We introduce a missing theoretical model, where we assume the emission comes from the spreading layer, the extension of the boundary layer between the accretion disk and the neutron star. We show how these models and the results of the simulations provide new insights into the x‐ray polarization from weakly magnetized neutron stars observed with the imaging x‐ray polarimetry explorer (IXPE). We specifically focus on the most peculiar case of the X‐ray burster GX 13+1.

Magnetar emergence in a peculiar gamma-ray burst from a compact star merger

Abstract The central engine that powers gamma-ray bursts (GRBs), the most powerful explosions in the universe, is still not identified. Besides hyper-accreting black holes, rapidly spinning and highly magnetized neutron stars, known as millisecond magnetars, have been suggested to power both long and short GRBs[1–8]. The presence of a magnetar engine following compact star mergers is of particular interest as it would provide essential constraints on the poorly understood equation of state for neutron stars[9,10]. Indirect indications of a magnetar engine in these merger sources have been observed in the form of plateau features present in the X-ray afterglow light curves of some short GRBs[11,12]. Additionally, some X-ray transients lacking gamma-ray bursts have been identified as potential magnetar candidates originating from compact star mergers[7,13,14]. Nevertheless, smoking gun evidence is still lacking for a magnetar engine in short GRBs, and associated theoretical challenges have been raised[15]. Here we present a comprehensive analysis of the broad-band prompt emission data of a peculiar, very bright GRB 230307A. Despite its apparently long duration, the prompt emission and host galaxy properties are consistent with a compact star merger origin, as suggested by its association with a kilonova[16]. Intriguingly, an extended X-ray emission component shows up as the γ-ray emission dies out, signifying the likely emergence of a magnetar central engine. We also identify an achromatic temporal break in the high-energy band during the prompt emission phase, which was never observed in previous bursts and reveals a narrow jet with half opening angle of ∼3.4○(RGRB/1015 cm)−1/2, where RGRB is the GRB prompt emission radius.

Observation of discontinuities accompanied by interplanetary shock within the Martian magnetosheath

As fast forward interplanetary (IP) shocks travel outward in the IP medium, they might encounter planetary bow shocks (BSs) and then propagate into the magnetosheath. The interaction of an IP shock with a BS could create a new discontinuity, which has been predicted by theory and simulations, and commonly observed at Earth. Nevertheless, it is still uncertain whether such a phenomenon occurs at unmagnetized planets like Mars. Here, we present the first experimental observation of a discontinuity-like structure that follows a transmitted IP shock within the Martian magnetosheath. This event was recorded by the MAVEN spacecraft on March 3, 2015. The comparison of spacecraft measurements with theoretical studies indicates that the discontinuity-like structure is a compound structure in nature, composed of the slow expansion wave, contact discontinuity, and slow shock, launched by the interaction of a fast IP shock with the Martian BS. The results shed light on the similarities between magnetized and unmagnetized planets in response to the passage of IP shocks.

Chemically peculiar stars as members of open clusters

ABSTRACT The chemically peculiar (CP) stars of the upper main sequence are excellent astrophysical laboratories to test the diffusion, mass-loss, rotational mixing, and pulsation in the (non-)presence of a stable local magnetic field. These processes are time-dependent. The age estimation of Galactic field stars suffers from several limitations. Therefore, studying members of star clusters overcomes these difficulties. We matched the most recently published catalogues of star clusters and CP stars. For the matching, we used the newest Gaia Data Release. We also used the $\Delta$a photometry tool to further distinguish between the CP subgroups. We found 595 CP stars in 408 star clusters of all ages. Furthermore, we report on misclassified metallic line stars (Am or CP1) and objects with no CP classification. The distribution of magnetic and non-magnetic CP stars on the main sequence seems different. We do not detect very young and very old CP stars showing rotationally induced variability. CP members of star clusters help to study all relevant processes responsible for this phenomenon in more detail. Still, a larger sample is desired to put tighter constraints on models.

Comprehensive analysis of the Apertif fast radio burst sample. Similarities with young energetic neutron stars

Understanding the origin of energetic fast radio bursts (FRBs) has become the main science driver of recent dedicated FRB surveys powered by real-time instrumentation. Between July 2019 and February 2022, we carried out ALERT, an FRB survey at 1370\,MHz using the Apertif Radio Transient System (ARTS) installed at the Westerbork Synthesis Radio Telescope (WSRT). Here we report the detection of 18 new FRBs. We studied the properties of the entire 24-burst sample that were detected during the survey. For five bursts, we identified host galaxy candidates within their error regions with >50<!PCT!> probability association. We observed an average linear polarisation fraction of $ and an average circular polarisation fraction consistent with 0<!PCT!>. One-third of the FRBs display multiple components. These burst structures and the polarisation fractions are strikingly similar to those observed in young energetic pulsars and magnetars. The Apertif FRBs next reveal a population of highly scattered bursts. Given the observing frequency and time resolution, the scattering of most FRBs is likely to have been produced in the immediate circumburst environment. Furthermore, two FRBs show evidence of high rotation measure values which could reach RM in the source reference frames. This corroborates that some source environments are dominated by magneto-ionic effects. Together, the scattering and rotation measures that ALERT has found prove that a large fraction of FRBs are embedded in complex media such as star-forming regions or supernova remnants. Through the discovery of FRB\,20200719A, the third most dispersed FRB so far, we further show that one-off FRBs emit at frequencies in excess of 6\,GHz, the highest known to date. We compare this to the radio-bright high-frequency emission seen in magnetars. Finally, we determine an FRB all-sky rate of above a fluence limit of 4.1\ and a fluence cumulative distribution with a power-law index pm0.2 $, which is roughly consistent with the Euclidean Universe predictions. Through the high resolution in time, frequency, polarisation, and localisation that ALERT featured, we were able to determine the morphological complexity, polarisation, local scattering and magnetic environment, and high-frequency luminosity of FRBs. We find all of these parameters strongly resemble those seen in young, energetic, highly magnetised neutron stars.

First Observation of the Complete Rotation Period of the Ultraslowly Rotating Magnetic O Star HD 54879

HD 54879 is the most recently discovered magnetic O-type star. Previous studies ruled out a rotation period shorter than 7 yr, implying that HD 54879 is the second most slowly rotating known magnetic O-type star. We report new high-resolution spectropolarimetric measurements of HD 54879, which confirm that a full stellar rotation cycle has been observed. We derive a stellar rotation period from the longitudinal magnetic field measurements of P=2562−58+63 days (about 7.02 yr). The radial velocity of HD 54879 has been stable over the last decade of observations. We explore equivalent widths and longitudinal magnetic fields calculated from lines of different elements, and conclude the atmosphere of HD 54879 is likely chemically homogeneous, with no strong evidence for chemical stratification or lateral abundance nonuniformities. We present the first detailed magnetic map of the star, with an average surface-magnetic-field strength of 2954 G, and a strength for the dipole component of 3939 G. There is a significant amount of magnetic energy in the quadrupole components of the field (23%). Thus, we find HD 54879 has a strong magnetic field with a significantly complex topology.

Impact of solar-wind turbulence on a planetary bow shock

Context. The interaction of the solar-wind plasma with a magnetized planet generates a bow-shaped shock ahead of the wind. Over recent decades, near-Earth spacecraft observations have provided insights into the physics of the bow shock, and the findings suggest that solar-wind intrinsic turbulence influences the bow shock dynamics. On the other hand, theoretical studies, primarily based on global numerical simulations, have not yet investigated the global three-dimensional (3D) interaction between a turbulent solar wind and a planetary magnetosphere. This paper addresses this gap for the first time by presenting an investigation of the global dynamics of this interaction that provides new perspectives on the underlying physical processes. Aims. We use the newly developed numerical code MENURA to examine how the turbulent nature of the solar wind influences the 3D structure and dynamics of magnetized planetary environments, such as those of Mercury, Earth, and magnetized Earth-like exoplanets. Methods. We used the hybrid particle-in-cell code MENURA to conduct 3D simulations of the turbulent solar wind and its interaction with an Earth-like magnetized planet through global numerical simulations of the magnetosphere and its surroundings. MENURA runs in parallel on graphics processing units, enabling efficient and self-consistent modeling of turbulence. Results. By comparison with a case in which the solar wind is laminar, we show that solar-wind turbulence globally influences the shape and dynamics of the bow shock, the magnetosheath structures, and the ion foreshock dynamics. Also, a turbulent solar wind disrupts the coherence of foreshock fluctuations, induces large fluctuations on the quasi-perpendicular surface of the bow shock, facilitates the formation of bubble-like structures near the nose of the bow shock, and modifies the properties of the magnetosheath region. Conclusions. The turbulent nature of the solar wind impacts the 3D shape and dynamics of the bow shock, magnetosheath, and ion foreshock region. This influence should be taken into account when studying solar-wind-planet interactions in both observations and simulations. We discuss the relevance of our findings for current and future missions launched into the heliosphere.

Incidence of afterglow plateaus in gamma-ray bursts associated with binary neutron star mergers

One of the most surprising gamma-ray burst (GRB) features discovered with the Swift X-ray telescope (XRT) is a plateau phase in the early X-ray afterglow light curves. These plateaus are observed in the majority of long GRBs, while their incidence in short GRBs (SGRBs) is still uncertain due to their fainter X-ray afterglow luminosity with respect to long GRBs. An accurate estimate of the fraction of SGRBs with plateaus is of utmost relevance given the implications that the plateau may have for our understanding of the jet structure and possibly of the nature of the binary neutron star (BNS) merger remnant. This work presents the results of an extensive data analysis of the largest and most up-to-date sample of SGRBs observed with the XRT, and for which the redshift has been measured. We find a plateau incidence of 18–37% in SGRBs, which is a significantly lower fraction than that measured in long GRBs (> 50%). Although still debated, the plateau phase could be explained as energy injection from the spin-down power of a newly born magnetized neutron star (NS; magnetar). We show that this scenario can nicely reproduce the observed short GRB (SGRBs) plateaus, while at the same time providing a natural explanation for the different plateau fractions between short and long GRBs. In particular, our findings may imply that only a minority of BNS mergers generating SGRBs leave behind a sufficiently stable or long-lived NS to form a plateau. From the probability distribution of the BNS remnant mass, a fraction 18–37% of short GRB plateaus implies a maximum NS mass in the range ∼2.3 − 2.35 M⊙.

Weakly Magnetized Accreting Neutron Stars as Seen by IXPE

ABSTRACTThe Imaging X‐ray Polarimetry Explorer, recently awarded by the American Astronomical Society with the Bruno Rossi prize, observed several accreting neutron stars in X‐ray binaries during the first 2 years of its prime mission. Results obtained for weakly magnetized neutron stars allow us to model the geometry and the physical status of the different emitting regions (accretion disk, boundary/spreading layer) in a completely novel way, showing a more intricate scenario with respect to the one initially anticipated based on theoretical models. In particular, polarization measurements have demonstrated variations with energy and time, which are highly intriguing. Here, a summary of the IXPE findings for these sources, in particular 4U 1820–303, and Cir X–1 are reported.