The recent detection of pulsations from the ultra luminous X-ray source (ULX) NuSTAR J095551+6940.8 in M82 by Bachetti et al. indicates that object is an accreting neutron star a high mass binary (HMXB) system. super-Eddington luminosity implies magnetic field sufficiently strong to suppress scattering cross-section unless its beam viewed at favourable angle. We show torque equilibrium condition for pulsar dipole $6.7 \times 10^{13}$ G, two orders magnitude higher than estimated al., and...

Deviations from the predictions of general relativity due to energy-momentum squared gravity (EMSG) are expected become pronounced in high density cores neutron stars. We derive hydrostatic equilibrium equations EMSG and solve them numerically obtain star mass-radius relations for four different realistic state. use existing observational measurements masses radii stars constrain free parameter, $\ensuremath{\alpha}$, that characterizes coupling between matter spacetime EMSG. show...

ABSTRACT The recently discovered rotationally powered pulsar PSR J1640–4631 is the first to have a braking index measured, with high enough precision, that greater than 3. An inclined magnetic rotator in vacuum or plasma would be subject not only spin-down but also an alignment torque. model can address for almost orthogonal rotator, which incompatible single-peaked pulse profile. dipole corotating predicts indices between 3 and 3.25. We find of 3.15 consistent two different inclination...

We study the general-relativistic dynamics of matter being accreted onto and ejected by a magnetised nonrotating neutron star. The is followed in framework fully general relativistic magnetohydrodynamics (GRMHD) within ideal-MHD limit two spatial dimensions. More specifically, making use numerical code BHAC, we follow evolution geometrically thick torus driven into accretion development magnetorotational instability. By number simulations which vary strength stellar dipolar magnetic field,...

The afterglow emission of some gamma-ray bursts (GRBs) show a shallow decay (plateau) phase implying continuous injection energy. source this energy is very commonly attributed to the spin-down power nascent millisecond magnetar. magnetic dipole radiation torque considered be mechanism causing neutron star. This has component working for alignment angle between rotation and axis, i.e., inclination angle, which been neglected in modelling GRB light curves. Here, we demonstrate evolution...

We study the structure of relativistic stars in $\mathcal{R}+\ensuremath{\alpha}{\mathcal{R}}^{2}$ theory using method matched asymptotic expansion to handle higher order derivatives field equations arising from curvature term. find solutions, parametrized by $\ensuremath{\alpha}$, for uniform density stars. obtain mass-radius relations and dependence maximum mass on $\ensuremath{\alpha}$. that ${M}_{\mathrm{max}}$ is almost linearly proportional For each $\ensuremath{\alpha}$ configuration...

ABSTRACT The distribution of the spin frequencies neutron stars in low-mass X-ray binaries exhibits a cut-off at 730 Hz, below break-up frequency (mass-shedding limit) stars. absence submillisecond pulsars presents problem, given that these systems are older than spin-up time-scale. We examine models disc–magnetosphere interaction near torque equilibrium balanced by due to gravitational wave emission. note field lines penetrating disc beyond inner radius reduce maximum rotation star, result...

The vacuum solutions around a spherically symmetric and static object in the Starobinsky model are studied with perturbative approach. differential equations for components of metric Ricci scalar obtained solved by using method matched asymptotic expansions. presence higher order terms this gravity leads to formation boundary layer near surface star allowing accommodation extra conditions on scalar. Accordingly, can be different from Schwarzschild solution depending value at while matching far star.

ABSTRACT Millisecond magnetars are often invoked as the central engine of some gamma-ray bursts (GRBs), specifically ones showing a plateau phase. We argue that an apparent phase may not be realized if magnetic field nascent magnetar is in transient rapid decay stage. Some GRBs lack clear also hosting millisecond magnetars. present approximate analytical solution coupled set equations describing evolution angular velocity and inclination angle between rotation axes neutron star presence...

ABSTRACT Some observations and numerical simulations of disc–magnetosphere interaction show that accretion can proceed in the propeller regime. When Alfvén radius is beyond corotation radius, matter climbs up to high latitudes where surface inside equilibrium accrete. We calculate fraction mass flux disc accrete onto neutron star depending on fastness parameter inclination angle between rotation magnetic axis. find that, for a narrow range parameter, surfaces intersect at two different...

The distribution of the spin frequencies neutron stars in low-mass X-ray binaries exhibits a cut-off at 730 Hz, below break-up frequency (mass-shedding limit) stars. absence sub-millisecond pulsars presents problem, given that these systems are older than spin-up timescale. We confront models disc-magnetosphere interaction near torque equilibrium balanced by due to gravitational wave emission. note field lines penetrating disc beyond inner radius reduce maximum rotation star, result...

Some models of gamma-ray bursts (GRBs) invoke nascent millisecond magnetars as the central engine and address X-ray afterglows with interaction magnetar magnetospheres fallback discs. We study evolution discs interacting magnetars. Initially, accretion rate in disc is very high, well above required for Eddington limit. The inner parts such a disc, even if it cooling by neutrino emission, get spherical due to radiation pressure, which regulates mass within spherization radius. Such can not...

Neutron stars might have multipole magnetic fields as implied by recent observations of pulsars. The presence the quadrupole field an effect on interaction between disc and neutron star depending location inner radius strength field. For a quadrudipole stellar field, we calculate toroidal generated within disc, magnetospheric torque exerted onto star. Also, deduce rotation which is relevant even for pure dipole fields.

Neutron stars might have multipole magnetic fields as implied by recent observations of pulsars. The presence the quadrupole field an effect on interaction between disc and neutron star depending location inner radius strength field. For a quadrudipole stellar field, we calculate toroidal generated within disc, magnetospheric torque exerted onto star. Also, deduce rotation which is relevant even for pure dipole fields.

Abstract Some models of gamma-ray bursts (GRBs) invoke nascent millisecond magnetars as the central engine and address X-ray afterglows with interaction magnetar magnetospheres fallback discs. We study evolution discs interacting magnetars. Initially, accretion rate in disc is very high, well above required for Eddington limit. The inner parts such a disc, even if it cooling by neutrino emission, get spherical due to radiation pressure, which regulates mass within spherization radius. Such...

We study the general-relativistic dynamics of matter being accreted onto and ejected by a magnetised nonrotating neutron star. The is followed in framework fully general relativistic magnetohydrodynamics (GRMHD) within ideal-MHD limit two spatial dimensions. More specifically, making use numerical code BHAC, we follow evolution geometrically thick torus driven into accretion development magnetorotational instability. By number simulations which vary strength stellar dipolar magnetic field,...

Some observations and numerical simulations of disc-magnetosphere interaction show that accretion can proceed in the propeller regime. When Alfvén radius is beyond corotation radius, matter climbs up to high latitudes where surface inside equilibrium accrete. We calculate fraction mass flux disc accrete onto neutron star depending on fastness parameter inclination angle between rotation magnetic axis. find that, for a narrow range parameter, surfaces intersect at two different critical...