547 research outputs found
Jet dynamics. Recollimation shocks and helical patterns
The dynamics and stability of extragalactic jets may be strongly influenced
by small (and probable) differences in pressure between the jet and the ambient
and within the jet itself. The former give rise to expansion and recollimation
of the jet. This occurs in the form of conical shocks, or Mach disks, if the
pressure difference is large enough. Pressure asymmetries within the jet may
trigger the development of helical patterns via coupling to kink current-driven
instability, or to helical Kelvin-Helmholtz instability, depending on the
physical conditions in the jet. I summarize here the evidence collected during
the last years on the presence of recollimation shocks and waves in jets. In
the jet of CTA 102 evidence has been found for (traveling)shock-(standing)shock
interaction in the core-region (0.1 mas from the core), using information from
the light-curve of the source combined with VLBI data. The conclusions derived
have been confirmed by numerical simulations combined with emission
calculations that have allowed to study the spectral evolution of the perturbed
jet. Helical structures can also be identified in radio-jets. The ridge-line of
emission of the jet of S5~0836+710 has been identified as a physical structure
corresponding to a wave developing in the jet flow. I review here the evidence
that has allowed to reach this conclusion, along with an associated caveat.
Current data do not allow to distinguish between magnetic or hydrodynamical
instabilities. I finally discuss the importance of these linear and non-linear
waves for jet evolution.Comment: 11 pages. Proceedings of the conference: The innermost regions of
relativistic jets and their magnetic fields. Corrected typos and added
reference
A numerical simulation of the evolution and fate of a FRI jet. The case of 3C 31
The evolution of FRI jets has been long studied in the framework of the
FRI-FRII dichotomy. In this paper, we test the present theoretical and
observational models via a relativistic numerical simulation of the jets in the
radio galaxy 3C 31. We use the parameters derived from the modelling presented
by \cite{lb02a,lb02b} as input parameters for the simulation of the evolution
of the source, thus assuming that they have not varied over the lifetime of the
source. We simulate about 10 % of the total lifetime of the jets in 3C 31.
Realistic density and pressure gradients for the atmosphere are used. The
simulation includes an equation of state for a two-component relativistic gas
that allows a separate treatment of leptonic and baryonic matter. We compare
our results with the modelling of the observational data of the source. Our
results show that the bow shock evolves self-similarly at a quasi-constant
speed, with slight deceleration by the end of the simulation, in agreement with
recent X-ray observations that show the presence of bow shocks in FRI sources.
The jet expands until it becomes underpressured with respect to the ambient
medium, and then recollimates. Subsequent oscillations around pressure
equilibrium and generation of standing shocks lead to the mass loading and
disruption of the jet flow. We derive an estimate for the minimum age of the
source of , which may imply continuous activity of 3C 31
since the triggering of its activity. The simulation shows that weak CSS
sources may be the young counterparts of FRIs. We conclude that the observed
properties of the jets in 3C 31 are basically recovered by the standing shock
scenario.Comment: Accepted for publication in MNRAS. For better quality figures, please
check http://www.mpifr-bonn.mpg.de/staff/mperucho/Research.htm
Jet stability, dynamics and energy transport
Relativistic jets carry energy and particles from compact to very large
scales compared with their initial radius. This is possible due to their
remarkable collimation despite their intrinsic unstable nature. In this
contribution, I review the state-of-the-art of our knowledge on instabilities
growing in those jets and several stabilising mechanisms that may give an
answer to the question of the stability of jets. In particular, during the last
years we have learned that the limit imposed by the speed of light sets a
maximum amplitude to the instabilities, contrary to the case of classical jets.
On top of this stabilising mechanism, the fast growth of unstable modes with
small wavelengths prevents the total disruption and entrainment of jets. I also
review several non-linear processes that can have an effect on the collimation
of extragalactic and microquasar jets. Within those, I remark possible causes
for the decollimation and decelleration of FRI jets, as opposed to the
collimated FRII's. Finally, I give a summary of the main reasons why jets can
propagate through such long distances.Comment: For the proceedings of High Energy Phenomena in Relativistic Outflows
III (HEPRO III, IJMPD, accepted). 12 page
Studying the interaction between microquasar jets and their environments
In high-mass microquasars (HMMQ), strong interactions between jets and
stellar winds at binary system scales could occur. In order to explore this
possibility, we have performed numerical 2-dimensional simulations of jets
crossing the dense stellar material to study how the jet will be affected by
these interactions. We find that the jet head generates strong shocks in the
wind. These shocks reduce the jet advance speed, and compress and heat up jet
and wind material. In addition, strong recollimation shocks can occur where
pressure balance between the jet side and the surrounding medium is reached.
All this, altogether with jet bending, could lead to the destruction of jets
with power . The conditions around the outflow shocks
would be convenient for accelerating particles up to TeV energies. These
accelerated particles could emit via synchrotron and inverse Compton (IC)
scattering if they were leptons, and via hadronic processes in case they were
hadrons.Comment: 4 pages. Contribution to the proceedings of High Energy Phenomena in
Relativistic Outflows, held in Dublin, Ireland, September 24-28, 200
Simulations of the relativistic parsec-scale jet in 3C273
We present a hydrodynamical 3D simulation of the relativistic jet in 3C273,
in comparison to previous linear perturbation analysis of Kelvin-Helmholtz
instability developing in the jet. Our aim is to assess advantages and
limitations of both analytical and numerical approaches and to identify spatial
and temporal scales on which the linear regime of Kelvin-Helmholtz instability
can be applied in studies of morphology and kinematics of parsec-scale jets.Comment: 4 pages, 3 figures; to be published in Proceedings of the workshop
"Multiband Approach to AGN", held on Sep.30-Oct.2 in Bonn. Publication:
Memorie della Societa Astronomica Italiana, v. 26, No.1 (2005). Reduced
figure resolution! Version with original figures is availavble at
http://www.mpifr-bonn.mpg.de/bonn04/proceedings/perucho.pd
3D simulations of wind-jet interaction in massive X-ray binaries
High-mass microquasars may produce jets that will strongly interact with
surrounding stellar winds on binary system spatial scales. We study the
dynamics of the collision between a mildly relativistic hydrodynamical jet of
supersonic nature and the wind of an OB star. We performed numerical 3D
simulations of jets that cross the stellar wind with the code Ratpenat. The jet
head generates a strong shock in the wind, and strong recollimation shocks
occur due to the initial overpressure of the jet with its environment. These
shocks can accelerate particles up to TeV energies and produce gamma-rays. The
recollimation shock also strengthens jet asymmetric Kelvin-Helmholtz
instabilities produced in the wind/jet contact discontinuity. This can lead to
jet disruption even for jet powers of several times erg s.
High-mass microquasar jets likely suffer a strong recollimation shock that can
be a site of particle acceleration up to very high energies, but also
eventually lead to the disruption of the jet.Comment: Accepted for publication in A&A Letter
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