278 research outputs found

### Vortical field amplification and particle acceleration at rippled shocks

Supernova Remnants (SNRs) shocks are believed to accelerate charged particles
and to generate strong turbulence in the post-shock flow. From high-energy
observations in the past decade, a magnetic field at SNR shocks largely
exceeding the shock-compressed interstellar field has been inferred. We outline
how such a field amplification results from a small-scale dynamo process
downstream of the shock, providing an explicit expression for the turbulence
back-reaction to the fluid whirling. The spatial scale of the $X-$ray rims and
the short time-variability can be obtained by using reasonable parameters for
the interstellar turbulence. We show that such a vortical field saturation is
faster than the acceleration time of the synchrotron emitting energetic
electrons.Comment: 4 pages, 3 figures; to appear in the proceedings of the RICAP-13,
Roma International Conference on AstroParticle Physic

### Early-time velocity autocorrelation for charged particles diffusion and drift in static magnetic turbulence

Using test-particle simulations, we investigate the temporal dependence of
the two-point velocity correlation function for charged particles scattering in
a time-independent spatially fluctuating magnetic field derived from a
three-dimensional isotropic turbulence power spectrum. Such a correlation
function allowed us to compute the spatial coefficients of diffusion both
parallel and perpendicular to the average magnetic field. Our simulations
confirm the dependence of the perpendicular diffusion coefficient on turbulence
energy density and particle energy predicted previously by a model for
early-time charged particle transport. Using the computed diffusion
coefficients, we exploit the particle velocity autocorrelation to investigate
the time-scale over which the particles "decorrelate" from the solution to the
unperturbed equation of motion. Decorrelation time-scales are evaluated for
parallel and perpendicular motions, including the drift of the particles from
the local magnetic field line. The regimes of strong and weak magnetic
turbulence are compared for various values of the ratio of the particle
gyroradius to the correlation length of the magnetic turbulence. Our simulation
parameters can be applied to energetic particles in the interplanetary space,
cosmic rays at the supernova shocks, and cosmic-rays transport in the
intergalactic medium.Comment: 10 pages, 11 figures, The Astrophyical Journal in pres

### On the physical processes which lie at the bases of time variability of GRBs

The relative-space-time-transformation (RSTT) paradigm and the interpretation
of the burst-structure (IBS) paradigm are applied to probe the origin of the
time variability of GRBs. Again GRB 991216 is used as a prototypical case,
thanks to the precise data from the CGRO, RXTE and Chandra satellites. It is
found that with the exception of the relatively inconspicuous but
scientifically very important signal originating from the initial ``proper
gamma ray burst'' (P-GRB), all the other spikes and time variabilities can be
explained by the interaction of the accelerated-baryonic-matter pulse with
inhomogeneities in the interstellar matter. This can be demonstrated by using
the RSTT paradigm as well as the IBS paradigm, to trace a typical spike
observed in arrival time back to the corresponding one in the laboratory time.
Using these paradigms, the identification of the physical nature of the time
variablity of the GRBs can be made most convincingly. It is made explicit the
dependence of a) the intensities of the afterglow, b) the spikes amplitude and
c) the actual time structure on the Lorentz gamma factor of the
accelerated-baryonic-matter pulse. In principle it is possible to read off from
the spike structure the detailed density contrast of the interstellar medium in
the host galaxy, even at very high redshift.Comment: 11 pages, 5 figure

### The EMBH model in GRB 991216 and GRB 980425

This is a summary of the two talks presented at the Rome GRB meeting by C.L.
Bianco and R. Ruffini. It is shown that by respecting the Relative Space-Time
Transformation (RSTT) paradigm and the Interpretation of the Burst Structure
(IBS) paradigm, important inferences are possible: a) in the new physics
occurring in the energy sources of GRBs, b) on the structure of the bursts and
c) on the composition of the interstellar matter surrounding the source.Comment: 8 pages, 3 figures, in the Proceedings of the "Third Rome Workshop on
Gamma-Ray Bursts in the Afterglow Era", 17-20 September 2002, M. Feroci, F.
Frontera, N. Masetti, L. Piro (editors

### The Space Environment and Atmospheric Joule Heating of the Habitable Zone Exoplanet TOI700-d

We investigate the space environment conditions near the Earth-size planet
TOI~700~d using a set of numerical models for the stellar corona and wind, the
planetary magnetosphere, and the planetary ionosphere. We drive our simulations
using a scaled-down stellar input and a scaled-up solar input in order to
obtain two independent solutions. We find that for the particular parameters
used in our study, the stellar wind conditions near the planet are not very
extreme -- slightly stronger than that near the Earth in terms of the stellar
wind ram pressure and the intensity of the interplanetary magnetic field. Thus,
the space environment near TOI700-d may not be extremely harmful to the
planetary atmosphere, assuming the planet resembles the Earth. Nevertheless, we
stress that the stellar input parameters and the actual planetary parameters
are unconstrained, and different parameters may result in a much greater effect
on the atmosphere of TOI700-d. Finally, we compare our results to solar wind
measurements in the solar system and stress that modest stellar wind conditions
may not guarantee atmospheric retention of exoplanets.Comment: accepted to Ap

### GRB 970228 Within the EMBH Model

We consider the gamma-ray burst of 1997 February 28 (GRB 970228) within the
ElectroMagnetic Black Hole (EMBH) model. We first determine the value of the
two free parameters that characterize energetically the GRB phenomenon in the
EMBH model, that is to say the dyadosphere energy, $E_{dya}=5.1\times10^{52}$
ergs, and the baryonic remnant mass $M_{B}$ in units of $E_{dya}$,
$B=M_{B}c^{2}/E_{dya}=3.0\times10^{-3}$. Having in this way estimated the
energy emitted during the beam-target phase, we evaluate the role of the
InterStellar Medium (ISM) number density (n$_{ISM}$) and of the ratio ${\cal
R}$ between the effective emitting area and the total surface area of the GRB
source, in reproducing the observed profiles of the GRB 970228 prompt emission
and X-ray (2-10 keV energy band) afterglow. The importance of the ISM
distribution three-dimensional treatment around the central black hole is also
stressed in this analysis.Comment: 4 pages, 1 figure, to appear in the Proceedings of the Los Alamos
"Gamma Ray Burst Symposium" in Santa Fe, New Mexico, September 8-12 2003 (AIP
Conf. Ser.), CHAPTER: GRB Connection to Supernova

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