scholarly journals GRB spectral parameter modeling

2010 ◽  
Vol 6 (S274) ◽  
pp. 243-245
Author(s):  
Gregory D. Fleishman ◽  
Fedor A. Urtiev
Keyword(s):  
Synchrotron Radiation ◽  
Electric Fields ◽  
Large Scale ◽  
Gamma Ray ◽  
Small Scale ◽  
Random Waves ◽  
Spectral Parameters ◽  
Random Magnetic Field ◽  
Cross Correlations ◽  
Accelerated Particles

AbstractFireball 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.

scholarly journals The Zone of Avoidance as an X-ray absorber - the role of the galactic foreground modelling Swift XRT spectra

2017 ◽  
Vol 12 (S333) ◽  
pp. 170-171
Author(s):  
I. I. Racz ◽  
Z. Bagoly ◽  
L. V. Tóth ◽  
L. G. Balázs ◽  
I. Horvath ◽  
...  
Keyword(s):  
Column Density ◽  
Large Scale ◽  
Gamma Ray ◽  
Small Scale ◽  
Prompt Gamma ◽  
Gamma Emission ◽  
Essential Information ◽  
X Ray ◽  
Hydrogen Column Density ◽  
Zone Of Avoidance

AbstractGamma-ray bursts (GRBs) are the most powerful explosive events in the Universe. The prompt gamma emission is followed by an X-ray afterglow that is also detected for over nine hundred GRBs by the Swift BAT and XRT detectors. The X-ray afterglow spectrum bears essential information about the burst, and the surrounding interstellar medium (ISM). Since the radiation travels through the line of sight intergalactic medium and the ISM in the Milky Way, the observed emission is influenced by extragalactic and galactic components. The column density of the Galactic foreground ranges several orders of magnitudes, due to both the large scale distribution of ISM and its small scale structures. We examined the effect of local HI column density on the penetrating X-ray emission, as the first step towards a precise modeling of the measured X-ray spectra. We fitted the X-ray spectra using the Xspec software, and checked how the shape of the initially power low spectrum changes with varying input Galactic HI column density. The total absorbing HI column is a sum of the intrinsic and Galactic component. We also investigated the model results for the intrinsic component varying the Galactic foreground. We found that such variations may alter the intrinsic hydrogen column density up to twenty-five percent. We will briefly discuss its consequences.

scholarly journals Behavior of compressed plasmas in magnetic fields

2020 ◽  
Vol 4 (1) ◽  
Author(s):  
Gurudas Ganguli ◽  
Chris Crabtree ◽  
Alex Fletcher ◽  
Bill Amatucci
Keyword(s):  
Electric Fields ◽  
Large Scale ◽  
Global Scale ◽  
Small Scale ◽  
Kinetic Regime ◽  
Plasma Dynamics ◽  
Formidable Challenge ◽  
Energy And Momentum ◽  
Intense Activity ◽  
Different Characteristics

AbstractPlasma in the earth’s magnetosphere is subjected to compression during geomagnetically active periods and relaxation in subsequent quiet times. Repeated compression and relaxation is the origin of much of the plasma dynamics and intermittency in the near-earth environment. An observable manifestation of compression is the thinning of the plasma sheet resulting in magnetic reconnection when the solar wind mass, energy, and momentum floods into the magnetosphere culminating in the spectacular auroral display. This phenomenon is rich in physics at all scale sizes, which are causally interconnected. This poses a formidable challenge in accurately modeling the physics. The large-scale processes are fluid-like and are reasonably well captured in the global magnetohydrodynamic (MHD) models, but those in the smaller scales responsible for dissipation and relaxation that feed back to the larger scale dynamics are often in the kinetic regime. The self-consistent generation of the small-scale processes and their feedback to the global plasma dynamics remains to be fully explored. Plasma compression can lead to the generation of electromagnetic fields that distort the particle orbits and introduce new features beyond the purview of the MHD framework, such as ambipolar electric fields, unequal plasma drifts and currents among species, strong spatial and velocity gradients in gyroscale layers separating plasmas of different characteristics, etc. These boundary layers are regions of intense activity characterized by emissions that are measurable. We study the behavior of such compressed plasmas and discuss the relaxation mechanisms to understand their measurable signatures as well as their feedback to influence the global scale plasma evolution.

scholarly journals A Bayesian approach to modelling multimessenger emission from blazars using lepto-hadronic kinetic equations

2020 ◽  
Vol 500 (3) ◽  
pp. 3613-3630 ◽  
Author(s):  
Bruno Jiménez-Fernández ◽  
Hendrik Jan van Eerten
Keyword(s):  
Large Scale ◽  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Kinetic Equations ◽  
Neutrino Flux ◽  
Spectral Energy ◽  
Acceleration Process ◽  
Emission Model ◽  
Statistical Tool ◽  
Cross Correlations

ABSTRACT Blazar TXS 0506+056 is the main candidate for a coincident neutrino and gamma-ray flare event. In this paper, we present a detailed kinetic lepto-hadronic emission model capable of producing a photon and neutrino spectrum given a set of parameters. Our model includes a range of large-scale geometries and both dynamical and steady-state injection models for electrons and protons. We link this model with a Markov chain Monte Carlo sampler to obtain a powerful statistical tool that allows us to both fit the Spectral Energy Distribution and study the probability density functions and correlations of the parameters. Assuming a fiducial neutrino flux, we demonstrate how multimessenger observations can be modelled jointly in a Bayesian framework. We find the best parameters for each of the variants of the model tested and report on their cross-correlations. Additionally, we confirm that reproducing the neutrino flux of TXS 0506+056 requires an extreme proton to electron ratio either in the local acceleration process or from external injection.

Electrorheological Dampers, Part II: Testing and Modeling

1996 ◽  
Vol 63 (3) ◽  
pp. 676-682 ◽  
Author(s):  
H. P. Gavin ◽  
R. D. Hanson ◽  
F. E. Filisko
Keyword(s):  
Steady Flow ◽  
Electric Fields ◽  
Curve Fitting ◽  
Material Properties ◽  
Large Scale ◽  
Modeling Technique ◽  
Small Scale ◽  
Multiple Dimensions ◽  
Strong Electric Fields ◽  
Limiting Case

Electrorheological (ER) materials develop yield stresses on the order of 5–10 kPa in the presence of strong electric fields. Viscoelastic and yielding material properties can be modulated within milli-seconds. An analysis of flowing ER materials in the limiting case of fully developed steady flow results in simple approximations for use in design. Small-scale experiments show that these design equations can be applied to designing devices in which the flow is unsteady. More exact models of ER device behavior can be determined using curve-fitting techniques in multiple dimensions. A previously known curve-fitting technique is extended to deal with variable electric fields. Experiments are described which illustrate the potential for ER devices in large-scale damping applications and the accuracy of the modeling technique.

How non-stationary are moderately supercritical shocks?

2019 ◽  
Vol 85 (5) ◽  
Author(s):  
Michael Gedalin
Keyword(s):  
Electric Fields ◽  
Large Scale ◽  
Small Scale ◽  
Particle Analysis ◽  
Main Role ◽  
Collisionless Shock ◽  
Pressure Balance ◽  
Ion Motion ◽  
Microscopic Field

Ion motion in a collisionless shock front is affected by macroscopic large-scale weakly varying and microscopic small-scale fast varying magnetic and electric fields. With the increase of the Mach number the role of the microscopic field is expected to become progressively more important. Using a combination of hybrid simulations and test particle analysis, we show that in moderately supercritical shocks macroscopic fields play the main role in ion motion across the shock. Pressure balance across the shock is only weakly broken and non-stationarity is related to the deviations from the total pressure from the constant value.

scholarly journals Radiation from accelerated particles in shocks

2011 ◽  
Vol 7 (S279) ◽  
pp. 371-372
Author(s):  
K.-I. Nishikawa ◽  
B. Zhang ◽  
E. J. Choi ◽  
K. W. Min ◽  
J. Niemiec ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Magnetic Fields ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Small Scale ◽  
Spectral Structure ◽  
Electron Positron ◽  
Jitter Radiation ◽  
Transverse Deflection ◽  
Accelerated Particles

AbstractRecent 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.

Multi-scale spatial distribution of K, Th and U in an Archaean potassic granite: a case study from the Heerenveen batholith, Barberton Granite-Greenstone Terrain, South Africa

2021 ◽  
Author(s):  
J-F. Moyen ◽  
M. Cuney ◽  
D. Baratoux ◽  
P. Sardini ◽  
S. Carrouée
Keyword(s):  
Large Scale ◽  
Gamma Ray ◽  
Shear Zones ◽  
Small Scale ◽  
Multi Scale ◽  
Gamma Ray Spectrometer ◽  
Rock Types ◽  
Large Scale Integration ◽  
Scale Integration

Abstract We describe the multi-scale distribution of K, Th and U in the ca. 3.1 Ga Heerenveen batholith of the Barberton Granite-Greenstone Terrain. Data were obtained with a combination of tools, including a portable gamma-ray spectrometer from the scale of the whole batholith to the scale of outcrops, and autoradiography for the thin section scale. U is concentrated preferentially in minor phases in the border shear zones of the batholith and, within these shear zones, in late pegmatites as well as fractures. The processes responsible for the concentration of U in the Heerenveen batholith is discussed in terms of magmatism, hydrothermalism (redistribution of U in fissures associated with magmato-hydrothermal fluids), and supergene alteration. The statistical properties of K, Th and U concentrations are different. K shows spatial correlation over large distance, largely mirroring mappable rock types, with increased variability at larger scales. In contrast, U is dominated by small-scale variations (“nugget effect”) and its variability is, averaged and smoothed by large-scale integration. Spatial and statistical features thus offer useful and complementary insights on petrogenetic and metallogenic processes in granitoids in addition to standard approaches (petrography, geochemistry).

scholarly journals Constraints on the primordial power spectrum of small scales using the neutrino signals from the dark matter decay

2014 ◽  
Vol 29 (32) ◽  
pp. 1450194 ◽  
Author(s):  
Yupeng Yang
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Large Scale ◽  
Gamma Ray ◽  
Neutrino Flux ◽  
Small Scale ◽  
Scale Invariant ◽  
Dark Matter Annihilation ◽  
Primordial Power Spectrum ◽  
Small Scales

Many inflation theories predict that the primordial power spectrum is scale invariant. The amplitude of the power spectrum can be constrained by different observations such as the cosmic microwave background (CMB), Lyman-α, large-scale structures and primordial black holes (PBHs). Although the constraints from the CMB are robust, the corresponding scales are very large (10-4 < k < 1 Mpc -1). For small scales (k > 1 Mpc -1), the research on the PBHs provides much weaker limits. Recently, ultracompact dark matter minihalos (UCMHs) was proposed and it was found that they could be used to constraint the small-scale primordial power spectrum. The limits obtained by the research on the UCMHs are much better than that of PBHs. Most of previous works focus on the dark matter annihilation within the UCMHs, but if the dark matter particles do not annihilate the decay is another important issue. In previous work [Y.-P. Yang, G.-L. Yang and H.-S. Zong, Europhys. Lett.101, 69001 (2013)], we investigated the gamma-ray flux from the UCMHs due to the dark matter decay. In addition to these flux, the neutrinos are usually produced going with the gamma-ray photons especially for the lepton channels. In this work, we studied the neutrino flux from the UCMHs due to the dark matter decay. Finally, we got the constraints on the amplitude of primordial power spectrum of small scales.

scholarly journals Multi-spacecraft observations of broadband waves near the lower hybrid frequency at the Earthward edge of the magnetopause

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1471-1481 ◽  
Author(s):  
M. André ◽  
R. Behlke ◽  
J.-E. Wahlund ◽  
A. Vaivads ◽  
A.-I. Eriksson ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Electric Field ◽  
Electric Fields ◽  
Large Scale ◽  
Small Scale ◽  
Lower Hybrid ◽  
Hybrid Frequency ◽  
Broadband Waves ◽  
Depression Wave ◽  
Magnetic Oscillations

Abstract. Broadband waves around the lower hybrid frequency (around 10 Hz) near the magnetopause are studied, using the four Cluster satellites. These waves are common at the Earthward edge of the boundary layer, consistent with earlier observations, and can have amplitudes at least up to 5 mV/m. These waves are similar on all four Cluster satellites, i.e. they are likely to be distributed over large areas of the boundary. The strongest electric fields occur during a few seconds, i.e. over distances of a few hundred km in the frame of the moving magnetopause, a scale length comparable to the ion gyroradius. The strongest magnetic oscillations in the same frequency range are typically found in the boundary layer, and across the magnetopause. During an event studied in detail, the magnetopause velocity is consistent with a large-scale depression wave, i.e. an inward bulge of magnetosheath plasma, moving tailward along the nominal magnetopause boundary. Preliminary investigations indicate that a rather flat front side of the large-scale wave is associated with a rather static small-scale electric field, while a more turbulent backside of the large-scale wave is associated with small-scale time varying electric field wave packets.Key words. Magnetospheric physics (magnetopause, cusp, and boundary layers) – Space plasma physics (waves and in-stabilities)

Small-Scale Science to Large-Scale Profession

2000 ◽  
Vol 45 (4) ◽  
pp. 396-398
Author(s):  
Roger Smith
Keyword(s):  
Large Scale ◽  
Small Scale
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