Search results for "Jet"
showing 10 items of 4711 documents
Evidence for shock-shock interaction in the jet of CTA 102
2010
We have found evidence for interaction between a standing and a traveling shock in the jet of the blazar CTA 102. Our result is based in the study of the spectral evolution of the turnover frequency-turnover flux density plane. The radio/mm light curves were taken during a major radio outburst in April 2006.
Does the plasma composition affect the long term evolution of relativistic jets?
2001
We study the influence of the matter content of extragalactic jets on their morphology, dynamics and emission properties. For this purpose we consider jets of extremely different compositions including pure leptonic and baryonic plasmas. Our work is based on two-dimensional relativistic hydrodynamic simulations of the long-term evolution of powerful extragalactic jets propagating into a homogeneous environment. The equation of state used in the simulations accounts for an arbitrary mixture of electrons, protons and electron-positron pairs. Using the hydrodynamic models we have also computed synthetic radio maps and the thermal Bremsstrahlung X-ray emission from their cavities. Although ther…
Resonant Kelvin-Helmholtz modes in sheared relativistic flows
2007
Qualitatively new aspects of the (linear and non-linear) stability of sheared relativistic (slab) jets are analyzed. The linear problem has been solved for a wide range of jet models well inside the ultrarelativistic domain (flow Lorentz factors up to 20; specific internal energies $\approx 60c^2$). As a distinct feature of our work, we have combined the analytical linear approach with high-resolution relativistic hydrodynamical simulations, which has allowed us i) to identify, in the linear regime, resonant modes specific to the relativistic shear layer ii) to confirm the result of the linear analysis with numerical simulations and, iii) more interestingly, to follow the instability develo…
Analytical and Numerical Studies of Fluid Instabilities in Relativistic Jets
2007
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 compare the model with the radio structure observed in 3C 273 on parsec scales using very long baseline interferometry (VLBI) and constrain the basic properties of the flow. Our results show that Kelvin-Helmholtz instabilities are the most p…
Off-Axis Properties of Short Gamma-Ray Bursts
2005
Based on recent models of relativistic jet formation by thermal energy deposition around black hole-torus systems, the relation between the on- and off-axis appearance of short, hard gamma-ray bursts (GRBs) is discussed in terms of energetics, duration, average Lorentz factor, and probability of observation, assuming that the central engines are remnants of binary neutron star or neutron star-black hole mergers. As a consequence of the interaction with the torus matter at the jet basis and the subsequent expansion of the jets into an extremely low-density environment, the collimated ultrarelativistic outflows possess flat core profiles with only little variation of radially-averaged propert…
Medium-modified jets in heavy-ion collisions
2010
The suppression of single inclusive hadron spectra in heavy-ion collision as compared to the scaled expectation from proton-proton collisions has long been regarded as an interesting tool to study properties of the bulk matter in heavy-ion collisions. However, the limitations of this class of observables has become increasingly obvious, and both experimental and theoretical efforts are now made to go beyond single hadrons to fully reconstructed jets. Monte-Carlo simulations of in-medium parton showers are currently considered the most promising tool to theoretically access jet physics in heavy-ion collisions. In this paper, I review some of the first results obtained with the MC code YaJEM …
Jet propagation through inhomogeneous media and shock ionization
2021
In this contribution we present the first numerical simulations of a relativistic outflow propagating through the inner hundreds of parsecs of its host galaxy, including atomic and ionised hydrogen, and the cooling effects of ionisation. Our results are preliminary, but we observe efficient shock ionization of atomic hydrogen in interstellar clouds. The mean density of the interstellar medium in these initial simulations is lower than that expected in typical galaxies, which makes cooling times longer and thus no recombination is observed inside the shocked region. The velocities achieved by the shocked gas in the simulations are in agreement with observational results, although with a wide…
Which physical parameters can be inferred from the emission variability of relativistic jets?
2005
We present results of a detailed numerical study and theoretical analysis of the dynamics of internal shocks in relativistic jets and the non-thermal flares associated with these shocks. In our model internal shocks result from collisions of density inhomogeneities (shells) in relativistic jet flows. We find that the merged shell resulting from the inelastic collision of shells has a complicated internal structure due to the non-linear dynamics of the interaction. Furthermore, the instantaneous efficiency for converting kinetic energy into thermal energy is found to be almost twice as high as theoretically expected during the period of significant emission. The Lorentz factors of the intern…
ChandraObservation of Cir X‐1 near the Periastron Passage: Evidence for an X‐Ray Jet?
2008
We present the results of a 25 ks long Chandra observation of the peculiar source Cir X-1 near the periastron passage. We report precise X-ray coordinates of the source, which were compatible with the optical and radio counterpart coordinates. We focus on the study of the detected emission features using the High Energy Transmission Grating Spectrometer on board the Chandra satellite. We detect emission lines associated with Mg XII, Si XIII, Si XIV, S XV, S XVI, Ar XVII, Ar XVIII, Ca XIX, Ca XX, Fe XXV, and Fe XXVI, showing an average redshift of 470 km s-1. The most intense emission features can be fitted with two lines; this is more evident for the 6.6 keV emission feature, which shows a …
The Complex Morphology of the X-ray and Optical Emission from HH 154: The Pulsed Jet Scenario
2009
We study the optical and X-ray emission from protostellar jets, focusing, in particular, on the case of HH 154. This project consists of two different and complementary approaches: the development of hydrodynamical models of the jet/ambient interaction, and the analysis of multi-wavelength observations. Comparing the results derived from the simulations with the observations we can infer the physical mechanisms leading to the complex morphology of the X-rays source observed at the base of HH 154.