6,140 research outputs found
Physical properties of the jet in 0836+710 revealed by its transversal structure
Studying the internal structure of extragalactic jets is crucial for
understanding their physics. The Japanese-led space VLBI project VSOP has
presented an opportunity for such studies, by reaching baseline lengths of up
to 36,000 km and resolving structures down to an angular size of
mas at 5 GHz. VSOP observations of the jet in 0836+710 at 1.6 and 5 GHz have
enabled tracing of the radial structure of the flow on scales from 2 mas to 200
mas along the jet and determination of the wavelengths of individual
oscillatory modes responsible for the formation of the structure observed. We
apply linear stability analysis to identify the oscillatory modes with modes of
Kelvin-Helmholtz instability that match the wavelengths of the structures
observed. We find that the jet structure in 0836+710 can be reproduced by the
helical surface mode and a combination of the helical and elliptic body modes
of Kelvin-Helmholtz instability. Our results indicate that the jet is
substantially stratified and different modes of the instability grow inside the
jet at different distances to the jet axis. The helical surface mode can be
driven externally, and we discuss the implications of the driving frequency on
the physics of the active nucleus in 0836+710.Comment: Accepted for publication in Astronomy & Astrophysics Letter
Extragalactic Relativistic Jets and Nuclear Regions in Galaxies
Past years have brought an increasingly wider recognition of the ubiquity of
relativistic outflows (jets) in galactic nuclei, which has turned jets into an
effective tool for investigating the physics of nuclear regions in galaxies. A
brief summary is given here of recent results from studies of jets and nuclear
regions in several active galaxies with prominent outflows.Comment: 5 pages; contribution to ESO Astrophysical Symposia, "Relativistic
Astrophysics and Cosmology", eds. B. Aschenbach, V. Burwitz, G. Hasinger, B.
Leibundgut (Springer: Heidelberg 2006
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
The resolved structure of the extragalactic supernova remnant SNR 4449-1
We present very long baseline interferometry (VLBI) observations of the
milliarcsecond-scale radio structure of the supernova remnant SNR 44491 in
the galaxy NGC 4449. This young and superluminous remnant was observed at 1.6
GHz (\,cm) with the European VLBI Network. The observations
confirm earlier identifications of this object with a supernova remnant (SNR)
while revealing a somewhat different morphology compared with the structure
reported by Bietenholz et al. from VLBI observations at 1.4 GHz. This
difference is discussed here in the context of structural sensitivity of both
observations. The 1.6 GHz image yields accurate estimates of the size (0.0422
arcsec 0.0285 arcsec and 0.8 0.5 pc) and age (55 yr) of
SNR 44491. With a total flux of 6.1 0.6 mJy measured in the VLBI
image, the historical lightcurve of the source can be well represented by a
power-law decay with a power index of 1.19 0.07. The SNR exhibits a
decline rate of the radio emission of 2.2 0.1 yr and a radio
luminosity of 1.74 10 erg s.Comment: 7 pages, 6 figures, MNRAS preprint, arXiv:1309.401
Derivation of the physical parameters of the jet in S5 0836+710 from stability analysis
A number of extragalactic jets show periodic structures at different scales
that can be associated with growing instabilities. The wavelengths of the
developing instability modes and their ratios depend on the flow parameters, so
the study of those structures can shed light on jet physics at the scales
involved. In this work, we use the fits to the jet ridgeline obtained from
different observations of S5 B0836710 and apply stability analysis of
relativistic, sheared flows to derive an estimate of the physical parameters of
the jet. Based on the assumption that the observed structures are generated by
growing Kelvin-Helmholtz (KH) instability modes, we have run numerical
calculations of stability of a relativistic, sheared jet over a range of
different jet parameters. We have spanned several orders of magnitude in
jet-to-ambient medium density ratio, and jet internal energy, and checked
different values of the Lorentz factor and shear layer width. This represents
an independent method to obtain estimates of the physical parameters of a jet.
By comparing the fastest growing wavelengths of each relevant mode given by the
calculations with the observed wavelengths reported in the literature, we have
derived independent estimates of the jet Lorentz factor, specific internal
energy, jet-to-ambient medium density ratio and Mach number. We obtain a jet
Lorentz factor , specific internal energy of , jet-to-ambient medium density ratio of , and an internal (classical) jet Mach number of . We also find that the wavelength ratios are better recovered by a
transversal structure with a width of of the jet radius. This
method represents a powerful tool to derive the jet parameters in all jets
showing helical patterns with different wavelengths.Comment: Accepted for publication in A&A, 15 pages, 12 figure
Anatomy of helical relativistic jets: The case of S5 0836+710
Helical structures are common in extragalactic jets. They are usually
attributed in the literature to periodical phenomena in the source (e.g.,
precession). In this work, we use VLBI data of the radio-jet in the quasar S5
0836+710 and hypothesize that the ridge-line of helical jets like this
corresponds to a pressure maximum in the jet and assume that the helically
twisted pressure maximum is the result of a helical wave pattern. For our
study, we use observations of the jet in S5 0836+710 at different frequencies
and epochs. The results show that the structures observed are physical and not
generated artificially by the observing arrays. Our hypothesis that the
observed intensity ridge-line can correspond to a helically twisted pressure
maximum is confirmed by our observational tests. This interpretation allows us
to explain jet misalignment between parsec and kiloparsec scales when the
viewing angle is small, and also brings us to the conclusion that
high-frequency observations may show only a small region of the jet flow
concentrated around the maximum pressure ridge-line observed at low
frequencies. Our work provides a potential explanation for the apparent
transversal superluminal speeds observed in several extragalactic jets by means
of transversal shift of an apparent core position with time.Comment: Accepted for publication in the Astrophysical Journa
The role of Kelvin-Helmholtz instability in the internal structure of relativistic outflows. The case of the jet in 3C 273
Relativistic outflows represent one of the best-suited tools to probe the
physics of AGN. Numerical modelling of internal structure of the relativistic
outflows on parsec scales provides important clues about the conditions and
dynamics of the material in the immediate vicinity of the central black holes
in AGN. We investigate possible causes of the structural patterns and
regularities observed in the parsec-scale jet of the well-known quasar 3C 273.
We present here the results from a 3D relativistic hydrodynamics numerical
simulation based on the parameters given for the jet by Lobanov & Zensus
(2001), and one in which the effects of jet precession and the injection of
discrete components have been taken into account. We compare the model with the
structures observed in 3C 273 using very long baseline interferometry and
constrain the basic properties of the flow. We find growing perturbation modes
in the simulation with similar wavelengths to those observed, but with a
different set of wave speeds and mode identification. If the observed longest
helical structure is produced by the precession of the flow, longer precession
periods should be expected. Our results show that some of the observed
structures could be explained by growing Kelvin-Helmholtz instabilities in a
slow moving region of the jet. However, we point towards possible errors in the
mode identification that show the need of more complete linear analysis in
order to interpret the observations. We conclude that, with the given viewing
angle, superluminal components and jet precession cannot explain the observed
structures.Comment: Accepted for publication in Astronomy & Astrophysics. 14 pages.
Higher resolution plots available on request to [email protected] and
at http://www.mpifr-bonn.mpg.de/staff/mperuch
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