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We study the interaction of relativistic jets with their environment, using 3-dimen- sional relativistic particle-in-cell simulations for two cases of jet composition: (i) electron-proton (e− − p+) and (ii) electron-positron (e±) plasmas containing helical magnetic fields. We have performed simulations of “global” jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities such as the Weibel instability, the kinetic Kelvin-Helmholtz instability and the Mushroom instability. We have found that these kinetic instabilities are suppressed and new types of instabilities can grow. For the e− − p+ jet, a recollimation-like instability occurs and jet electrons are strongly perturbed, whereas for the e± jet, a recollimation-like instability occurs at early times followed by kinetic instability and the general structure is similar to a simulation without a helical magnetic field. We plan to perform further simulations using much larger systems to confirm these new findings.
We investigated particle acceleration and shock structure associated with an unmagnetized
relativistic jet propagating into an unmagnetized plasma. Strong magnetic fields generated
in the trailing shock contribute to the electrons transverse deflection and acceleration.
We have calculated, self-consistently, the radiation from electrons accelerated in these
turbulent magnetic fields. We found that the synthetic spectra depend on the bulk Lorentz
factor of the jet, its temperature and strength of the generated magnetic fields. We have
also investigated accelerated electrons in strong magnetic fields generated by kinetic
shear (Kelvin-Helmholtz) instabilities. The calculated properties of the emerging
radiation will guide our understanding of the complex time evolution and/or spectral
structure in gamma-ray bursts, relativistic jets in general, and supernova remnants.
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has properties different from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We present synthetic spectra to compare with the spectra obtained from Fermi observations.
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has different properties from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We will present detailed spectra for conditions relevant to various astrophysical sites of collisionless shock formation. In particular we will discuss application to GRBs and SNRs.
A confocal x-ray fluorescence microscope was built at the Cornell High Energy Synchrotron Source (CHESS) to determine the composition of buried paint layers that range from 10–80 μm thick in paintings. The microscope consists of a borosilicate monocapillary optic to focus the incident beam and a borosilicate polycapillary lens to collect the fluorescent x-rays. The overlap of the two focal regions is several tens of microns in extent, and defines the active, or confocal, volume of the microscope. The capabilities of the technique were tested using acrylic paint films with distinct layers brushed onto glass slides and a twentieth century oil painting on canvas. The position and thickness of individual layers were extracted from their fluorescence profiles by fitting to a simple, semi-empirical model.
We report on microstructure, mechanical properties and wear resistance of Fe-Al based alloys with various alloying elements. The microstructures were examined using optical and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscope (EDS). Two types of alloys were prepared using vacuum arc melting; one is Fe-28Al based alloys (D03 structured) with and without alloying elements such as Mo and Zr. The other one is Fe-35Al based alloys (B2 structured) produced with same manner. For both types of alloys, equiaxed microstructures were observed by the addition of Mo, while dendritic structures were observed by the Zr addition. These microstructural features were more evinced with increasing the content of alloying elements. Concerning the mechanical properties and wear resistance, Fe-35Al based alloys with or without Mo addition superior to Fe-28Al based alloys especially in the high temperature region.
We present the analysis of emission line spectra of AGNs and
starbursts with the help of models coupling shocks and photoionization
by AGNs and by massive stars. We show how shocks and photoionization
by the central source have to coexist in AGNs in order to reproduce
the observed emission line ratios. We also show how stellar photoionization
models can be reconciled with the values of the [OI]/Hα and
[SII]/Hα ratios observed in starbursts, without requiring an additional
ionizing source such as shocks.
Using integral field spectroscopy, we detected the broad features
of massive Wolf-Rayet stars in the core of three Seyfert galaxies.
The observed high value of the WR/O number ratio is a clear signature
of a young and powerful starburst. The star-forming regions are distributed
in an arc/ring-like structure around the AGN, at a distance
of about 200 pc. These are the first spatially-resolved detections of
massive starbursts so close of an AGN.
Adaptive Optics Systems are now routinely operated on several
4 meter class telescopes, allowing to achieve angular resolutions
down to 70 msec in the near-infrared. Although these Systems have excellent
performances, their use for exploring the physics and structure
of AGN is still limited for the following reasons: the limiting magnitude
of the wavefront sensor is too high, the sensitivity of infrared
detectors does not give access to medium/high spectral resolution spectroscopy
and the angular resolution achieved does not always fit the
apparent size of the physical components responsible for emission features
close to the central engine. The new generation of 8 — 10 m class
telescopes bring improvements in this matter. However, some interesting
results have been obtained so far with Adonis, the ESO La Silla
adaptive optics System on the 3.60 meter telescope, in the investigation
of AGN structure. In particular, a prominent structure has been
detected in the central arcsec core of NGC 1068, which might feature
the dusty/molecular torus expected on theoretical grounds.
The dynamics of a massive binary System in a galactic nucleus are presented.
These are the first results from simulations applying a hybrid "self consistent field"
(SCF) 1 and direct Aarseth N body integrator (NBODY6) 2, which synthesises
the advantages of the direct force calculation with the efficiency of the field method.
The code is aimed for use on parallel architectures and is therefore applicable
for collisional N-body integrations with extraordinarily large particle numbers
(> 105). It opens the perspective to simulate the dynamics of globular clusters with
realistic collisional relaxation, as well as stellar Systems surrounding a supermassive
black hole in galactic nuclei.
The main characteristics of the average spectrum of radio
quiet AGN in the UV and X-ray range are reviewed, and the emission
mechanisms are discussed in the framework of accretion disk models,
in particular the "irradiated cold relativistic disk". It is shown that
some problems arise in confronting the predictions of the model to the
observations. We propose an alternative model in terms of a hot disk
surrounded by a cold Compton thick medium. Finally we mention
problems with remote regions of the accretion disk.
The modclling of plasma outfiows from central gravitating
objects such as AGN is bricfly discussed via analytic examples in the
context of ideal MHD. The exact solutions are produced via a nonlinear
separation of the variables in the full set of the MHD equations. Attention
is given to the questions of initial acceleration and collimation
of the outflow. A quantitative: criterion is provided for the transition of
the morphologies from highly collimated jets to non collimated winds.
Hydrodynamical simulations have played an important role
in the understanding of extragalactic jets since the late seventies. In
this talk, recent simulations of jets in the relativistic regime are reviewed.
Special attention is payed to simulations of jets at parsec scale
which, for the first time. have allowed to probe the current models of
superluminal radio sources.
The development of a variety of non-electromagnetic detectors
will drastically enlarge our global view on Galactic Nuclei and
AGNs in the future. The possibility of detecting their non-photonic
emission, namely ultra-high energy cosmic rays (UHECRs) and gravitational
waves, may open new Windows on AGN physics in coming
We are interested in the stellar content in the central region
of active galaxies. In this aim, we perform stellar population synthesis
of the integrated starlight in the Optical and NIR using a mathematical
method (Pelat, 1997, MNRAS 284, 365) dedicated to the determination
of the best solution (among the many local solutions) in the stellar
population synthesis problem which is a complex inverse problem. A
new development of the code allows the determination of the error zone
around the solution, expected from the observational uncertainties. In
the next sections, we present this very powerful method and results
obtained from a sample of AGN.
The narrow emission line luminosities of radio-loud AGN are
well-correlated with their low-frequcncy radio luminosities. This correlation
is linear and extends over at least four orders of magnitude. The
correlation is discussed in terms of a linear relationship between the
power in the radio-emitting jets and the photoionizing (i.e. accretion)
luminosity. Support for this theory comes from a direct correlation between
the optical continuum and radio luminosities of steep-spectrum
quasars. We discuss the dependence of the observed luminosities of
AGN on their black hole masses and how close to the Eddington limit
they are accreting.