Narrow Results

In this work, we discuss white dwarf pulsars found recently making also reference of the possibility of some SGRs/AXPs being part of this class of pulsars. We also study the properties of very massive compact ultra magnetized white dwarfs that could be the progenitors candidates of super luminous type Ia supernovae, and also a previous stage of these white dwarf pulsars before the magnetic field decay.The structure of this ultra magnetized white dwarfs is obtained by solving the Einstein-Maxwell equations with a poloidal magnetic field in a fully general relativistic approach. The stellar interior is composed of a regular crystal lattice made of carbon ions immersed in a degenerate relativistic electron gas. We find that magnetized white dwarfs violate the standard Chandrasekhar mass limit significantly. We obtain a maximum white dwarf mass of around $2.12M_{\odot }$ with an equatorial radius $R\sim 1596$ Km, a central magnetic field of $B_c=1.74\times 10^{14}$ G and $B_s=3.6\times 10^{13}$ G at the stellar surface.

In this work, we study the effects of different magnetic field configurations in neutron stars described by a many-body forces formalism (MBF model). The MBF model is a relativistic mean field formalism that takes into account many-body forces by means of a meson field dependence of the nuclear interaction coupling constants. We choose the best parametrization of the model that reproduces nuclear matter properties at saturation and also describes massive neutron stars. We assume matter to be in beta-equilibrium, charge neutral and at zero temperature. Magnetic fields are taken into account both in the equation of state and in the structure of the stars by the self-consistent solution of the Einstein-Maxwell equations. We assume a poloidal magnetic field distribution and calculate its effects on neutron stars, showing its influence on the gravitational mass and deformation of the stars.

Neutron stars manifest themselves as different classes of astrophysical sources that are associated to distinct phenomenology. Here we focus our attention on magnetars (or strongly magnetized neutron stars) that are associated to Soft Gamma Repeaters and Anomalous X-ray Pulsars. The magnetic field on surface of these objects, reaches values greater than $10^{15}$ G. Under intense magnetic fields, relativistic effects begin to be decisive for the definition of the structure and evolution of these objects. We are tempted to question ourselves to how strengths fields affect the structure of neutron star. In this work, our objective is study and compare two solutions of Einstein-Maxwell equations: the Bonnor solution, which is an analytical solution that describe the exterior spacetime for a massive compact object which has a magnetic field that is characterize as a dipole field and a complete solution that describe the interior and exterior spacetime for the same source found by numerical methods). For this, we describe the geodesic equations generated by such solutions. Our results show that the orbits generated by the Bonnor solution are the same as described by numerical solution. Also, show that the inclusion of magnetic fields with values up to $10^{17}$G in the center of the star does not modify sharply the particle orbits described around this star, so the use of Schwarzschild solution for the description of these orbits is a reasonable approximation.

It appears that studying data from the catalogue of Gamma-Ray Bursts (GRBs) can be used to examine the birefringence phenomenon in the magnetosphere of the magnetars. By analysing the data from the McGill Online Magnetar and HEASARC Fermi Burst Catalogues, in this work we studied the angular distances between GRBs and magnetars in projection, we built their distribution map by the end of 2020, and the relative lag time periods of lights coming from GRBs and magnetars. It is confirmed that there are 29 galactic magnetars and their candidates, while the other two are located out of the Milkyway. The maximum separation angle for GRB and Magnetar projectiles was 3.76 degrees (4U0142+61 and GRB110818860), while minimum angular resolution was 0.54 degrees (SGR 1627-41 and GRB090829672). Currently, we discuss the relationship of GRB light intensity by their lag time as it would come after bending in the magnetosphere of the magnetar.

In 2013 April a new magnetar, SGR1745−2900, was discovered as it entered an outburst, at an angular separation of only 2.4 arcsec from the supermassive black hole at the centre of the Milky Way, Sagittarius A*. The new source was detected both in the radio and X-ray bands, with a peak X-ray luminosity L_X ∼ 5 × 10³⁵ erg s⁻¹, and it has a spin-down magnetic field of ∼ 2 × 10¹⁴ G. Here we report on the long-term Chandra (twenty-six observations) and XMM–Newton (eight observations) X-ray monitoring campaign of SGR 1745−2900 from the onset of the outburst in 2013 April until 2014 September. This magnetar shows a slow flux decay compared to other magnetars and a rather inefficient surface cooling. Starquake-induced crustal cooling models alone have difficulty in explaining the high luminosity of the source for the first ∼200 d of its outburst. Additional heating of the star surface from currents flowing in a twisted magnetic bundle is probably playing an important role in the outburst evolution.

We consider anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) as rotationally powered pulsar-like white dwarfs. For the spin-down power of the white dwarf we use the traditional dipole braking formula as well as two other more recent and realistic models provided by numerical studies of the magnetosphere of a compact object including the wind braking torque. We show that, for the inferred values of the structure parameters and magnetic field obtained from the observed rotation period and spin-down rates, these white dwarfs are located above the so-called death-line. This result allows us to explain the blackbody component observed in the soft X-ray band of SGRs and AXPs via the polar caps’ heating by the bombardment of back flowing pair-created particles. For the sake of example, we show our results for the case of 1E 2259+586.