Narrow Results

It is shown that electron gas in dense stellar matter exhibit super-fluid (frictionless) like property if the magnetic field strength is high enough to populate only the zeroth Landau levels, i.e. it is possible that at the core of a magnetar, the proton matter behaves like a superconductor, neutron matter behaves like a super-fluid and electron gas shows super-fluidity without superconductivity. Therefore, the core region as a whole of a magnetar may behave like a frictionless matter which is quite surprising.

In this paper, timing data for anomalous X-ray pulsars and soft gamma repeaters are compiled. Timing properties of these objects are investigated. The effect of bursts of soft gamma repeaters on their period history is investigated. The diagram for pulsars, X-ray binaries, anomalous X-ray pulsars, soft gamma repeaters and dim radio quiet neutron stars is constructed. The possible evolutionary tracks for anomalous X-ray pulsars, soft gamma repeaters and dim radio quiet neutron stars are examined.

The coincidence excess between the gravitational wave detectors EXPLORER and NAUTILUS observed in the ten-day period 7–17 September 1998 is the largest ever observed. The event occurred mainly at the sidereal hour 4, when the detectors axes were perpendicular to the Galactic disk. This excess occurred during a period of intense activity of the black hole candidate XTE J1550-564, and within days of the giant flare from the magnetar SGR1900+14.

We model the evolution of the magnetic fields of neutron stars as consisting of a long term power-law decay modulated by short term small amplitude oscillations. Our model predictions on the timing noise of neutron stars agree well with the observed statistical properties and correlations of normal radio pulsars. Fitting the model predictions to the observed data, we found that their initial parameter implies their initial surface magnetic dipole magnetic field strength B₀ ~ 5 × 10¹⁴ G when t₀ = 0.4 yr and that the oscillations have amplitude K ~ 10^-8 to 10^-5 and period T on the order of years. For individual pulsars our model can effectively reduce their timing residuals, thus offering the potential of more sensitive detections of gravitational waves with pulsar timing arrays. Finally our model can also re-produce their observed correlation and oscillations of , as well as the "slow glitch" phenomenon.

We analyze the magnetic field evolution in dense quark matter with unbroken chiral symmetry, which can be found inside quark and hybrid stars. The magnetic field evolves owing to the chiral magnetic effect in the presence of the electroweak interaction between quarks. In our study, we also take into account the magnetohydrodynamic turbulence effects in dense quark matter. We derive the kinetic equations for the spectra of the magnetic helicity density and the magnetic energy density as well as for the chiral imbalances. On the basis of the numerical solution of these equations, we find that turbulence effects are important for the behavior of small scale magnetic fields. It is revealed that, under certain initial conditions, these magnetic fields behave similarly to the electromagnetic flashes of some magnetars. We suggest that fluctuations of magnetic fields, described in frames of our model, which are created in the central regions of a magnetized compact star, can initiate magnetar bursts.

An accepted model for magnetospheric substorms is used as the basis for a generic model for magnetic explosions, Emphasis is placed on the role of the inductive electric field and the displacement current. It is pointed out that these are unjustifiably neglected in conventional models, with this neglect being implicit in the assumptions of magnetohydrodynamics. Consequences of including the inductive electric field are identified. Fiducial numbers for the application of the generic model to solar flares and magnetar outbursts are suggested.

Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are enigmatic pulsar-like objects. The energy budget is the fundamental problem in their studies. In the magnetar model, they are supposed to be powered by the extremely strong magnetic fields (≳ 10¹⁴G) of neutron stars. Observations for and against the magnetar model are both summarized. Considering the difficulties encountered by the magnetar model to comfortably understand more and more observations, one may doubt that AXPs and SGRs are really magnetars. If they are not magnetar candidates (including magnetar-based models), then they must be "quark star/fallback disk" systems.

Since their initial discovery, the origin of isolated white dwarfs (WDs) with magnetic fields in excess of ~1 MG has remained a mystery. Recently, the formation of these high-field magnetic WDs has been observationally linked to strong binary interactions incurred during post-main-sequence evolution. Planetary, brown dwarf or stellar companions located within a few AU of main-sequence stars may become engulfed during the primary's expansion off the main sequence. Sufficiently low-mass companions in-spiral inside a common envelope until they are tidally shredded near the natal white dwarf. Formation of an accretion disk from the disrupted companion provides a source of turbulence and shear which act to amplify magnetic fields and transport them to the WD surface. We show that these disk-generated fields explain the observed range of magnetic field strengths for isolated, high-field magnetic WDs. Additionally, we discuss a high-mass binary analogue which generates a strongly-magnetized WD core inside a pre-collapse, massive star. Subsequent core-collapse to a neutron star may produce a magnetar.

Gamma-ray bursts (GRBs) are the brightest explosions in the universe, yet the properties of their energy sources are far from understood. Very important clues, however, can be deduced by studying the afterglows of these events. We present observations of GRB 130831A and its afterglow obtained with Swift, Chandra, and multiple ground-based observatories. This burst shows an uncommon drop in the X-ray light curve at about 100 ks after the trigger, with a decay slope of α ≃ 7. The standard Forward Shock (FS) model offers no explanation for such a behaviour. Instead, a model in which a newly born magnetar outflow powers the early X-ray emission is found to be viable. After the drop, the X-ray afterglow resumes its decay with a slope typical of FS emission. The optical emission, on the other hand, displays no clear break across the X-ray drop and its decay is consistent with that of the late X-rays. Using both the X-ray and optical data, we show that the FS model can explain the emission after ≃ 100 ks. We model our data to infer the kinetic energy of the ejecta and thus estimate the efficiency of a magnetar “central engine” of a GRB. Furthermore, we break down the energy budget of this GRB into prompt emission, late internal dissipation, kinetic energy of the relativistic ejecta, and compare it with the energy of the accompanying supernova, SN 2013fu.

We study polar Alfvén oscillations of relativistic stars endowed with a strong global poloidal dipole magnetic field. Here we focus only on the axisymmetric oscillations which are studied by evolving numerically the two-dimensional perturbation equations. Our study shows that the spectrum of the polar Alfvén oscillations is discrete in contrast to the spectrum of axial Alfvén oscillations which is continuous. We also show that the typical fluid modes, such as the f and p modes, are not significantly affected by the presence of the strong magnetic field.

We study the self-interaction of a massive scalar field with a point-like particle in a Kerr resp. Schwarzschild background black hole space-times. We find that in addition to regularization of the self-field a finite renormalization of the particle mass is also necessary to obtain a unique equation of motion. We expand the renormalized equation of motion for large scalar masses and apply this approximation for the neutral pion radiation by protons in the strong electromagnetic field of a magnetar. Our results show that taking into account general relativistic effects to leading order has a significant influence on the proton energy and the intensity of neutral pion radiation.

Here, we first analyze data from two GPS stations operating in Tashkent and Kitab and new Very Low Frequency (VLF) radio receiver operating in Tashkent for the possible earthquake ionospheric precursors. We find anomalous Total Electron Content (TEC) precursor signals and significant correlation in time between the TEC anomalies and the occurrence of the earthquake in Tashkent on August 22, 2008, M = 4.4. The obtained results have revealed a fine agreement with the TEC anomalies observed during the strong earthquake in Tashkent and we demonstrate the capabilities of the GPS technique to detect ionospheric perturbations caused by the local earthquakes. TEC decrease during the solar eclipse on August 1, 2008 is also obtained from the data at GPS stations in Tashkent and Kitab. We used tweek radio atmospherics (originating from lightning discharges) to estimate electron densities in the D-layer of ionosphere. The propagation characteristics of tweek atmospherics observed at the Tashkent station have been studied near the mode cut-off frequencies. It is shown that the height of the Earth-Ionosphere Wave Guide (EIWG) varies from 84 km to 91 km and nighttime electron density varies from 25 el/cm³ to 27 el/cm³. We have also studied VLF amplitude anomalies related to the earthquakes occurring on the path from the VLF transmitters to the Tashkent station. For analyzing narrowband data we have used the Nighttime Fluctuation method paying attention to the data obtained during the local nighttime (18:00 LT- 06:00 LT). The deathlines for rotating as well as oscillating magnetars are obtained for the different modes of oscillations and it is shown that the oscillations increase the region in the (P is the period) diagram of the magnetars which is allowed for the radio emission.

The magnetars are believed to be highly magnetized neutron stars having surface magnetic field 10¹⁴ – 10¹⁵ G. It is believed that at the center, the magnetic field may be higher than that at the surface. We study the effect of the magnetic field on the neutron star matter. We model the nuclear matter with the relativistic mean field approach considering the possibility of appearance of hyperons at higher density. We find that the effect of magnetic field on the matter of neutron stars and hence on the mass-radius relation is important, when the central magnetic field is at least of the order of 10¹⁷ G. Very importantly, the effect of strong magnetic field reveals anisotropy to the system. Moreover, if the central field approaches 10¹⁹ G, then the matter becomes unstable which limits the maximum magnetic field at the center of magnetars.

Fast radio bursts (FRBs) are millisecond-duration radio flashes with extremely high bright temperatures but unknown origin(s). The Five-hundred-meter aperture spherical radio telescope (FAST) is one of the perfect facilities for pulsar-related sciences owing to the high sensitivity, especially FRBs, which is phenomenologically similar to pulsars’ individual pulses. As expected, FAST has had a profound impact on FRB science since its operation in 2019. The discovery of more sources and deeper characterisations of their properties are key to understanding their physical origin(s) and radiation mechanism. In this chapter, we will review FAST’s achievements in the field of FRB in only a few short years.

Though the great progress has been understood from the multi-band observations and theoretical work since the discovery of pulsar more than fifty years ago, some basic problems are not solved, such as radiation process in pulsating ultraluminous X-ray source, the origins of fast radio burst and so on. X-ray observations could supply crucial information to understand the characteristics and behaviors of pulsars. Recently, some progress for these basic problems has been achieved via the observations of Insight-HXMT.

Though great progress has been achieved from the multi-band observations and theoretical work since the discovery of pulsars more than 50 years ago, some basic problems, such as radiation process in pulsating ultraluminous X-ray source, the origins of fast radio burst and so on. X-ray observations could supply crucial information to understand the characteristics and behaviors of pulsars. Recently, some progress for these basic problems has been achieved via the observations of Insight-HXMT.