171 research outputs found
Funnel-flow accretion onto highly magnetized neutron stars and shock generation
In this paper, we initiate a new study of steady funnel-flow accretion onto
strongly magnetized neutron stars, including a full treatment of shock
generation. As a first step, we adopt a simplified model considering the flow
within Newtonian theory and neglecting radiative pressure and cooling. The flow
is taken to start from an accretion disc and then to follow magnetic field
lines, forming a transonic funnel flow onto the magnetic poles. A standing
shock occurs at a certain point in the flow and beyond this material accretes
subsonically onto the star with high pressure and density. We calculate the
location of the standing shock and all other features of the flow within the
assumptions of our model. Applications to observed X-ray pulsars are discussed.Comment: 18 pages, 5 figs, accepted to Progress of Theoretical Physic
The Fate of Dead Radio-loud Active Galactic Nuclei: A New Prediction of Long-lived Shell Emission
We examine the fate of a dead radio source in which jet injection from the
central engine has stopped at an early stage of its evolution ( yr). To this aim, we theoretically evaluate the evolution of the
emission from both the lobe and the shell, which are composed of shocked jet
matter and a shocked ambient medium, respectively. Based on a simple dynamical
model of expanding lobe and shell, we clarify how the broadband spectrum of
each component evolves before and after the cessation of the jet activity. It
is shown that the spectrum is strongly dominated by the lobe emission while the
jet is active (). On the other hand, once the jet activity has
ceased (), the lobe emission fades out rapidly, since fresh electrons
are no longer supplied from the jet. Meanwhile, shell emission only shows a
gradual decrease, since accelerated electrons are continuously supplied from
the bow shock that is propagating into the ambient medium. As a result, overall
emission from the shell overwhelms that from the lobe at wide range of
frequencies from radio up to gamma-ray soon after the jet activity has ceased.
Our result predicts a new class of dead radio sources that are dominated by
shell emission. We suggest that the emission from the shell can be probed in
particular at a radio wavelengths with the Square Kilometer Array (SKA) phase
1.Comment: 9 pages, 3 figures, accepted for publication in Ap
Hydrodynamical effects in internal shock of relativistic outflows
We study both analytically and numerically hydrodynamical effects of two
colliding shells, the simplified models of the internal shock in various
relativistic outflows such as gamma-ray bursts and blazars. We pay particular
attention to three interesting cases: a pair of shells with the same rest mass
density (``{\it equal rest mass density}''), a pair of shells with the same
rest mass (``{\it equal mass}''), and a pair of shells with the same bulk
kinetic energy (``{\it equal energy}'') measured in the intersteller medium
(ISM) frame. We find that the density profiles are significantly affected by
the propagation of rarefaction waves. A split-feature appears at the contact
discontinuity of two shells for the ``equal mass'' case, while no significant
split appears for the ``equal energy'' and ``equal rest mass density'' cases.
The shell spreading with a few ten percent of the speed of light is also shown
as a notable aspect caused by rarefaction waves. The conversion efficiency of
the bulk kinetic energy to internal one is numerically evaluated. The time
evolutions of the efficiency show deviations from the widely-used inellastic
two-point-mass-collision model.Comment: 29 pages, 16 figures, accepted by Ap
- …