95 research outputs found
Diffusive synchrotron radiation from extragalactic jets
Flattenings of nonthermal radiation spectra observed from knots and interknot
locations of the jets of 3C273 and M87 in UV and X-ray bands are discussed
within modern models of magnetic field generation in the relativistic jets.
Specifically, we explicitly take into account the effect of the small-scale
random magnetic field, probably present in such jets, which gives rise to
emission of Diffusive Synchrotron Radiation, whose spectrum deviates
substantially from the standard synchrotron spectrum, especially at high
frequencies. The calculated spectra agree well with the observed ones if the
energy densities contained in small-scale and large-scale magnetic fields are
comparable. The implications of this finding for magnetic field generation,
particle acceleration, and jet composition are discussed.Comment: 5 pages with 2 figures, MNRAS Letters, accepte
GRB spectral parameter modeling
Fireball model of the gamma-ray bursts (GRBs) predicts generation of numerous
internal shocks, which efficiently accelerate charged particles and generate
relatively small-scale stochastic magnetic and electric fields. The accelerated
particles diffuse in space due to interaction with the random waves and so emit
so called Diffusive Synchrotron Radiation (DSR) in contrast to standard
synchrotron radiation they would produce in a large-scale regular magnetic
fields. In this contribution we present key results of detailed modeling of the
GRB spectral parameters, which demonstrate that the non-perturbative DSR
emission mechanism in a strong random magnetic field is consistent with
observed distributions of the Band parameters and also with cross-correlations
between them.Comment: 3 pages; IAU symposium # 274 "Advances in Plasma Astrophysics
Radio emission from acceleration sites of solar flares
The Letter takes up a question of what radio emission is produced by
electrons at the very acceleration site of a solar flare. Specifically, we
calculate incoherent radio emission produced within two competing acceleration
models--stochastic acceleration by cascading MHD turbulence and regular
acceleration in collapsing magnetic traps. Our analysis clearly demonstrates
that the radio emission from the acceleration sites: (i) has sufficiently
strong intensity to be observed by currently available radio instruments and
(ii) has spectra and light curves which are distinctly different in these two
competing models, which makes them observationally distinguishable. In
particular, we suggest that some of the narrowband microwave and decimeter
continuum bursts may be a signature of the stochastic acceleration in solar
flares.Comment: ApJL, in pres
Diffusive Synchrotron Radiation from Relativistic Shocks of Gamma-Ray Burst Sources
The spectrum of electromagnetic emission generated by relativistic electrons
scattered on small-scale random magnetic fields, implied by current models of
the magnetic field generation in the gamma-ray burst sources, is considered.
The theory developed includes both perturbative and non-perturbative versions
and, therefore, suggests a general treatment of the radiation in arbitrary
small-scale random field. It is shown that a general treatment of the random
nature of the small-scale magnetic field, as well as angular diffusion of the
electrons due to multiple scattering by magnetic inhomogeneities (i.e.,
non-perturbative effects), give rise to a radiation spectrum that differs
significantly from so-called "jitter" spectrum. The spectrum of diffusive
synchrotron radiation seems to be consistent with the low energy spectral index
distribution of the gamma-ray bursts.Comment: 15 pages, 2 figures, accepted for ApJ. Typo removed. More discussion
added. Wording adjusted to ApJ style: "errors" replaced with
"oversimplifications" or s
3D simulations of gyrosynchrotron emission from mildly anisotropic nonuniform electron distributions in symmetric magnetic loops
Microwave emission of solar flares is formed primarily by incoherent
gyrosynchrotron radiation generated by accelerated electrons in coronal
magnetic loops. The resulting emission depends on many factors, including
pitch-angle distribution of the emitting electrons and the source geometry. In
this work, we perform systematic simulations of solar microwave emission using
recently developed tools (GS Simulator and fast gyrosynchrotron codes) capable
of simulating maps of radio brightness and polarization as well as spatially
resolved emission spectra. A 3D model of a symmetric dipole magnetic loop is
used. We compare the emission from isotropic and anisotropic (of loss-cone
type) electron distributions. We also investigate effects caused by
inhomogeneous distribution of the emitting particles along the loop. It is
found that effect of the adopted moderate electron anisotropy is the most
pronounced near the footpoints and it also depends strongly on the loop
orientation. Concentration of the emitting particles at the loop top results in
a corresponding spatial shift of the radio brightness peak, thus reducing
effects of the anisotropy. The high-frequency (around 50 GHz) emission spectral
index is specified mainly by the energy spectrum of the emitting electrons;
however, at intermediate frequencies (around 10-20 GHz), the spectrum shape is
strongly dependent on the electron anisotropy, spatial distribution, and
magnetic field nonuniformity. The implications of the obtained results for the
diagnostics of the energetic electrons in solar flares are discussed.Comment: ApJ in press. 20 pp, 13 figs, on-line album and simulation source
code availabl
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