Timing Properties of Shocked Accretion Flows around Neutron Stars in presence of cooling. (arXiv:1901.10529v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bhattacharjee_A/0/1/0/all/0/1">Ayan Bhattacharjee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chakrabarti_S/0/1/0/all/0/1">Sandip K. Chakrabarti</a>
We carry out the first robust numerical simulation of accretion flows on a
weakly magnetized neutron star using Smoothed Particle Hydrodynamics (SPH). We
follow the Two-Component Advective Flow (TCAF) paradigm for black holes, and
focus only on the advective component for the case of a neutron star. This low
viscosity sub-Keplerian flow will create a normal boundary layer (or, NBOL)
right on the star surface in addition to the centrifugal pressure supported
boundary layer (or, CENBOL) present in a black hole accretion. These density
jumps could give rise to standing or oscillating shock fronts. During a hard
spectral state, the incoming flow has a negligible viscosity causing more
sub-Keplerian component as compared to the Keplerian disc component. We show
that our simulation of flows with a cooling and a negligible viscosity produces
precisely two shocks and strong supersonic winds from these boundary layers. We
find that the specific angular momentum of matter dictates the locations and
the nature of oscillations of these shocks. For low angular momentum flows, the
radial oscillation appears to be preferred. For flows with higher angular
momentum, the vertical oscillation appears to become dominant. In all the
cases, asymmetries w.r.t. the Z=0 plane are seen and instabilities set in due
to the interaction of inflow and outgoing strong winds. Our results capture
both the low and high-frequency quasi-periodic oscillations without invoking
magnetic fields or any precession mechanism. Most importantly, these solutions
directly corroborate observed features of wind dominated high-mass X-ray
binaries, such as Cir X-1.
We carry out the first robust numerical simulation of accretion flows on a
weakly magnetized neutron star using Smoothed Particle Hydrodynamics (SPH). We
follow the Two-Component Advective Flow (TCAF) paradigm for black holes, and
focus only on the advective component for the case of a neutron star. This low
viscosity sub-Keplerian flow will create a normal boundary layer (or, NBOL)
right on the star surface in addition to the centrifugal pressure supported
boundary layer (or, CENBOL) present in a black hole accretion. These density
jumps could give rise to standing or oscillating shock fronts. During a hard
spectral state, the incoming flow has a negligible viscosity causing more
sub-Keplerian component as compared to the Keplerian disc component. We show
that our simulation of flows with a cooling and a negligible viscosity produces
precisely two shocks and strong supersonic winds from these boundary layers. We
find that the specific angular momentum of matter dictates the locations and
the nature of oscillations of these shocks. For low angular momentum flows, the
radial oscillation appears to be preferred. For flows with higher angular
momentum, the vertical oscillation appears to become dominant. In all the
cases, asymmetries w.r.t. the Z=0 plane are seen and instabilities set in due
to the interaction of inflow and outgoing strong winds. Our results capture
both the low and high-frequency quasi-periodic oscillations without invoking
magnetic fields or any precession mechanism. Most importantly, these solutions
directly corroborate observed features of wind dominated high-mass X-ray
binaries, such as Cir X-1.
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