Thermodynamic analysis of the reduction annealing of iron powder. Part I

Syrovat-skii, É. F.; Shvartsman, V. L.; Pavlov, A. I.; Gaiduchenko, A. K.

doi:10.1007/bf00790788

Cited by 4 publications

(5 citation statements)

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“…The transport of the escaping electrons from the loop legs to FPs is described by the classical thick target model (Brown 1971;Syrovat-Skii & Shmeleva 1972;Petrosian 1973). The radiating electron flux spectrum integrated over the whole thick target, but mainly at the FPs, produced by the escaping electrons is given by (e.g., Park et al 1997)…”

Section: Bremsstrahlung Hxr Radiationmentioning

confidence: 99%

“…where N tr eff is given by Equation ( 10). It should be noted that as a result of the density dependence of the Coulomb energy loss rate, the thick target radiating electron spectrum X FP and consequently the bremsstrahlung photon spectrum J FP are independent of the thick target density profile (e.g., Syrovat-Skii & Shmeleva 1972;Park et al 1997).…”

Section: Bremsstrahlung Hxr Radiationmentioning

confidence: 99%

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Determination of Stochastic Acceleration Model Characteristics in Solar Flares

Chen

Petrosian

2013

ApJ

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Following our recent paper, we have developed an inversion method to determine the basic characteristics of the particle acceleration mechanism directly and non-parametrically from observations under the leaky box framework. Earlier, we demonstrated this method for obtaining the energy dependences of the escape time and pitch angle scattering time. Here, by converting the Fokker-Planck equation to its integral form, we derive the energy dependences of the energy diffusion coefficient and direct acceleration rate for stochastic acceleration in terms of the accelerated and escaping particle spectra. Combining the regularized inversion method of Piana et al. and our procedure, we relate the acceleration characteristics in solar flares directly to the count visibility data from RHESSI. We determine the timescales for electron escape, pitch angle scattering, energy diffusion, and direct acceleration at the loop top acceleration region for two intense solar flares based on the regularized electron flux spectral images. The X3.9 class event shows dramatically different energy dependences for the acceleration and scattering timescales, while the M2.1 class event shows a milder difference. The discrepancy between the M2.1 class event and the stochastic acceleration model could be alleviated by a turbulence spectrum that is much steeper than the Kolmogorov-type spectrum. A likely explanation of the X3.9 class event could be that the escape of electrons from the acceleration region is not governed by a random walk process, but instead is affected by magnetic mirroring, in which the scattering time is proportional to the escape time and has an energy dependence similar to the energy diffusion time.

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Section: Bremsstrahlung Hxr Radiationmentioning

confidence: 99%

Section: Bremsstrahlung Hxr Radiationmentioning

confidence: 99%

Determination of Stochastic Acceleration Model Characteristics in Solar Flares

Chen

Petrosian

2013

ApJ

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“…In the range of energies we are interested in, the spectrum of the produced electrons and positrons is affected by propagation mainly through radiative losses, therefore for simplicity we neglect here the role of escape of electrons from the Galaxy, which play a role only below 10 GeV. In this case, the solution of the diffusion equation for an individual supernova remnant is [43]:…”

Section: The Positron Flux From Pulsarsmentioning

confidence: 99%

Positrons from pulsar winds

Blasi

Amato

2010

High-Energy Emission From Pulsars and Their Systems

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Pulsars, or more generally rotation powered neutron stars, are excellent factories of antimatter in the Galaxy, in the form of pairs of electrons and positrons. Electrons are initially extracted from the surface of the star by the intense rotation induced electric fields and later transformed into electron-positron pairs through electromagnetic cascading. Observations of Pulsar Wind Nebulae (PWNe) show that cascades in the pulsar magnetosphere must ensure pair multiplicities of order 10 4 − 10 5 . These pairs finally end up as part of the relativistic magnetized wind emanating from the pulsar. The wind is slowed down, from its highly relativistic bulk motion, at a termination shock, which represents the reverse shock due to its interaction with the surrounding ejecta of the progenitor supernova. At the (relativistic) termination shock, acceleration of the pairs occurs, as part of the dissipation process, so that the cold wind is transformed into a plasma of relativistic non-thermal particles, plus a potential thermal component, which however has never been observed. As long as the pulsar wind is embedded in the supernova remnant these pairs are forced to escavate a bubble and lose energy adiabatically (because of the expansion) and radiatively (because of magnetic and radiation fields). We discuss here the observational constraints on the energy and number content of such pairs and discuss the scenarios that may allow for the pairs to escape in the interstellar medium and possibly contribute to the positron excess that has recently been detected by the PAMELA satellite. Special attention is dedicated to the case of nebulae surrounding high speed pulsars, observationally classified as Pulsar Bow Shock Nebulae. The pairs produced in these objects may be effectively carried out of the Supernova Remnant and released in the Interstellar Medium. As a result, Bow Shock Pulsar Wind Nebulae might be the main contributors to the positron excess in the Galaxy.

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“…Hoyng et al 1981;Saint-Hilaire et al 2008). This has been interpreted in terms of the collisional thick target model (Brown 1971;Syrovat-Skii & Shmeleva 1972;Hudson 1972;Petrosian 1973), in which nonthermal electrons move downward from the corona to the chromosphere and radiate most of the HXR emission at the dense FP regions. This simple model with a beam of electrons injected into a coronal loop does not predict a distinct HXR source from the tenuous corona except at very low energies, say below ∼20 keV (e.g.…”

Section: Introductionmentioning

confidence: 99%

Impulsive Phase Coronal Hard X-Ray Sources in an X3.9 Class Solar Flare

Chen

Petrosian

2012

ApJ

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We present analysis of a pair of unusually energetic coronal hard X-ray (HXR) sources detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during the impulsive phase of an X3.9 class solar flare on 2003 November 3, which simultaneously shows two intense footpoint (FP) sources. A distinct loop top (LT) coronal source is detected up to ∼150 keV and a second (upper) coronal source up to ∼80 keV. These photon energies, which were not fully investigated in earlier analysis of this flare, are much higher than commonly observed in coronal sources and pose grave modeling challenges. The LT source in general appears higher in altitude with increasing energy and exhibits a more limited motion compared to the expansion of the thermal loop. The high energy LT source shows an impulsive time profile and its nonthermal power law spectrum exhibits soft-hard-soft evolution during the impulsive phase, similar to the FP sources. The upper coronal source exhibits an opposite spatial gradient and a similar spectral slope compared to the LT source. These properties are consistent with the model of stochastic acceleration of electrons by plasma waves or turbulence. However, the LT and FP spectral index difference (varying from ∼0-1) is much smaller than commonly measured and than that expected from a simple stochastic acceleration model. Additional confinement or trapping mechanisms of high energy electrons in the corona are required. Comprehensive modeling including both kinetic effects and the macroscopic flare structure may shed light on this behavior. These results highlight the importance of imaging spectroscopic observations of the LT and FP sources up to high energies in understanding electron acceleration in solar flares. Finally, we show that the electrons producing the upper coronal HXR source may very likely be responsible for the type III radio bursts at the decimetric/metric wavelength observed during the impulsive phase of this flare.

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Thermodynamic analysis of the reduction annealing of iron powder. Part I

Cited by 4 publications

References 0 publications

Determination of Stochastic Acceleration Model Characteristics in Solar Flares

Determination of Stochastic Acceleration Model Characteristics in Solar Flares

Positrons from pulsar winds

Impulsive Phase Coronal Hard X-Ray Sources in an X3.9 Class Solar Flare

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