Gravitational waves from SGRs and AXPs as fast-spinning white dwarfs

ABSTRACT In our previous article we have explored the continuous gravitational waves (GWs) emitted from rotating magnetized white dwarfs (WDs) and their detectability by the planned GW detectors such as Laser Interferometer Space Antenna (LISA), Deci-hertz Interferometer Gravitational wave Observatory (DECIGO), and Big Bang Observer (BBO). Here, GWs’ emission due to magnetic deformation mechanism is applied for soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs), described as fast-spinning and magnetized WDs. Such emission is caused by the asymmetry around the rotation axis of the star generated by its own intense magnetic field. Thus, for the first time in the literature, the GW counterparts for SGRs/AXPs are described as WD pulsars. We find that some SGRs/AXPs can be observed by the space detectors BBO and DECIGO. In particular, 1E 1547.0−5408 and SGR 1806−20 could be detected in 1 yr of observation, whereas SGR 1900+14, CXOU J171405.7−381031, Swift J1834.9−0846, SGR 1627−41, PSR J1622−4950, SGR J1745−2900, and SGR 1935+2154 could be observed with a 5-yr observation time. The sources XTE J1810−197, SGR 0501+4516, and 1E 1048.1−5937 could also be seen by BBO and DECIGO if these objects have $M_{\mathrm{ WD}} \lesssim 1.3 \, \mathrm{M}_{\odot }$ and $M_{\mathrm{ WD}} \lesssim 1.2 \, \mathrm{M}_{\odot }$, respectively. We also found that SGRs/AXPs as highly magnetized neutron stars are far below the sensitivity curves of BBO and DECIGO. This result indicates that a possible detection of continuous GWs originated from these objects would corroborate the WD pulsar model.

Are fast radio bursts made by neutron stars?

ABSTRACT Popular models of repeating fast radio bursts (FRBs; and perhaps of all FRBs) involve neutron stars because of their high rotational or magnetostatic energy densities. These models take one of two forms: giant but rare pulsar-like pulses like those of rotating radio transients, and outbursts like those of soft gamma repeaters. Here I collate the evidence, recently strengthened, against these models, including the absence of Galactic micro-FRBs, and attribute the 16 d periodicity of FRB 180916.J0158+65 to the precession of a jet produced by a massive black hole’s accretion disc.

Equatorial Geodesics Around the Magnetars

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 [Formula: see text] 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 [Formula: see text]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.

SGRs/AXPs as Rotation-Powered Neutron Stars

We show that nine soft gamma repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs) of the twenty three known sources can be described as rotation-powered canonical pulsars. To accomplish this we use realistic parameters of rotating neutron stars obtained from numerical integration of the self-consistent axisymmetric general relativistic equations of equilibrium. We present limits to the NS mass where the sources can be rotation-powered.