21 research outputs found
Effect of angular opening on the dynamics of relativistic hydro jets
Context. Relativistic jets emerging from AGN cores transfer energy from the
core to their surrounding ISM/IGM. Because jets are observed to have finite
opening angles, one needs to quantify the role of conical versus cylindrical
jet propagation in this energy transfer. Aims. We use FR-II AGN jets parameter
with finite opening angles. We study the effect of the variation of the opening
angle on the dynamics and energy transfer of the jet. We also point out how the
characteristics of this external medium, such as its density profile, play a
role in the dynamics. Methods. This study exploits our parallel AMR code
MPI-AMRVAC with its special relativistic hydrodynamic model, incorporating an
equation of state with varying effective polytropic index. We studied mildly
under-dense jets up to opening angles of 10 degrees, at Lorentz factors of
about 10, inspired by observations. Instantaneous quantification of the various
ISM volumes and their energy content allows one to quantify the role of mixing
versus shock-heated cocoon regions over the time intervals. Results. We show
that a wider opening angle jet results in a faster deceleration of the jet and
leads to a wider cocoon dominated by Kelvin-Helmholtz and Rayleigh-Taylor
instabilities. The energy transfer mainly occurs in the shocked ISM region by
both the frontal bow shock and cocoon-traversing shock waves, in a roughly 3 to
1 ratio to the energy transfer of the mixing zone, for a 5 degree opening angle
jet. A rarefaction wave induces a dynamically formed layered structure of the
jet beam. Conclusions. Finite opening angle jets can efficiently transfer
significant fractions (25 % up to 70 %) of their injected energy over a growing
region of shocked ISM matter. The role of the ISM stratification is prominent
for determining the overall volume that is affected by relativistic jet
injection
Circular geodesics and thick tori around rotating boson stars
Accretion disks play an important role in the evolution of their relativistic
inner compact objects. The emergence of a new generation of interferometers
will allow to resolve these accretion disks and provide more information about
the properties of the central gravitating object. Due to this instrumental leap
forward it is crucial to investigate the accretion disk physics near various
types of inner compact objects now to deduce later constraints on the central
objects from observations. A possible candidate for the inner object is the
boson star. Here, we will try to analyze the differences between accretion
structures surrounding boson stars and black holes. We aim at analysing the
physics of circular geodesics around boson stars and study simple thick
accretion tori (so-called Polish doughnuts) in the vicinity of these stars. We
realize a detailed study of the properties of circular geodesics around boson
stars. We then perform a parameter study of thick tori with constant angular
momentum surrounding boson stars. This is done using the boson star models
computed by a code constructed with the spectral solver library KADATH. We
demonstrate that all the circular stable orbits are bound. In the case of a
constant angular momentum torus, a cusp in the torus surface exists only for
boson stars with a strong gravitational scalar field. Moreover, for each inner
radius of the disk, the allowed specific angular momentum values lie within a
constrained range which depends on the boson star considered. We show that the
accretion tori around boson stars have different characteristics than in the
vicinity of a black hole. With future instruments it could be possible to use
these differences to constrain the nature of compact objects.Comment: Accepted for publication in CQ
Relativistic 3D jet simulations for the X-ray binary SS433
Context. Modern high resolution observations allow to view closer into the
objects powering relativistic jets. This is especially the case for SS433, an
X-ray binary from which a precessing jet is observed down to the sub-parsec
scale.
Aims. We want to study full 3D dynamics of relativistic jets associated with
AGN or XRB. We study the precessing motion of a jet as a model for the jet
associated with the XRB SS433. Our study of the jet dynamics in this system
focuses on the sub-parsec scales. We investigate the impact of jet precession
and the variation of the Lorentz factor of the injected matter on the general
3D jet dynamics and its energy transfer to the surrounding medium. We realize
synthetic radio mapping of the data, to compare our results with observations.
Methods. For our study we use the code MPI-AMRVAC with SRHD model of a
baryonic jet. We use a AMR scheme and an inner time-dependent boundary
prescription to inject the jets. Parameters extracted from observations were
used. 3D jet realizations that match the SS433 jet are intercompared. We track
the energy content, as deposited in different regions of the domain affected by
the jet. Our code also follows a population of particles injected with the jet.
This evolving energy spectrum of accelerated electrons, allows to obtain the
radio emission from our simulation.
Results. we obtain meaningful observations. We find increased energy transfer
for a precessing jet compared to a standing jets. We obtain synthetic radio
maps for all jets.
Conclusions. The synthetic radio map matches best for a model using the
canonical kinematic model. Overdense precessing jets experience significant
deceleration in their propagation through the ISM, and while the overall jet is
of helical shape. This argument show that the kinematic model for SS433
assuming ballistic propagation has to be corrected for this decelretaion.Comment: Accepted for publication in Astrophysic and Astronom
Shock-cloud interaction and gas-dust spatial separation
© 2017 ESO. Context. We revisit the study of shocks interacting with molecular clouds, incorporating coupled gas-dust dynamics. Aims. We study the effect of different parameters on the shock-cloud interaction, such as the dust-to-gas ratio or the Mach number of the impinging shock. By solving self-consistently for drag-coupled gas and dust evolutions, we can assess the frequently made assumption that the dust is locked to the dynamics of the gas so that dust observations would result in direct information on the gas distribution. Methods. We used a multi-fluid model where the dust is represented by grain-size specific pressureless fluids. The dust and gas interact through a drag force, and we used four dust species with weighted representative sizes between 1 and 500 nm. We use the open source code MPI-AMRVAC for a parametric study of the effect of the gas-dust ratio and the Mach number of the shock. By using the radiative transfer code SKIRT, we create synthetic millimeter wavelength maps to connect to observations. Results. We find that the presence of dust does not significantly affect the dynamics of the gas for realistic dust-gas ratios, and this is the case throughout the range of Mach numbers explored (1.5-10). For high Mach numbers, we find a significant discrepancy between the distribution of the dust and gas after the cloud-shock interaction with the larger dust species clearly lagging the heavily mixed and accelerated gas (re)distribution. Conclusions. We conclude that observational studies of dusty environments may need to account for clearly separated spatial distributions of dust and gas, especially those studies that are representative of molecular clouds that have been interacting with high Mach number shock fronts.status: publishe
The SS433 jet from subparsec to parsec scales
Context. Relativistic jets associated with compact objects, as in the
X-ray binary SS433, are known to be multiscale because they spawn over many orders of
magnitude in distance. Here we model the precessing SS433 jet and study its dynamics from (0.01)
to (1)
parsec scales.
Aims. We aim to solve the discrepancy between the observations on a 0.1
pc scale of SS433, where the jet is clearly precessing with an angle of 20°, and the larger scale
observations where the jet of SS433 interacts with the associated supernova remnant W50,
requiring a precessing angle of 10°.
Methods. We use 3D special relativistic hydrodynamical simulations on a
domain of a scale of 1 pc. We use the finite volume code MPI-AMRVAC, solving the
relativistic variant of the Euler equations. To cover lengthscale variations from
(0.001)
pc as the jet beam width up to the domain size, we take full advantage of code
parallelization and its adaptive mesh refinement scheme.
Results. We found that by means of a simple hydrodynamical process, the
jet of SS433 can transit from a precessing jet with an angle of 20°, to a continuous hollow
non-precessing jet with a smaller opening angle of about 10°. Successive windings of the
precessing jet helix undergo gradual deceleration by ISM interaction, to ultimately merge
in a hollow straight jet at distances where the ram pressure of individual jet elements
match the ISM pressure at about 0.068 pc from the source.
Conclusions. We solve the discrepancy with an elegant and simple model
that does not require the jet of SS433 to undergo any temporal changes in jet injection
dynamics, but does so as a consequence of a hydrodynamically enforced spatial
recollimation. Our simulation thus serves to validate simpler model prescriptions for
SS433 on large scales, where a continuous jet profile suffices