Particle Acceleration by Magnetic Reconnection

Litvinenko, Yuri E.

doi:10.1007/3-540-36242-8_13

Cited by 10 publications

(2 citation statements)

References 38 publications

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“…Although shock-acceleration has been most frequently used to explain synchrotron emission from hot stars, other mechanisms such as magnetic reconnection are also capable of accelerating particles to relativistic speeds (e.g. Litvinenko 2003).…”

Section: Introductionmentioning

confidence: 99%

Can single O stars produce non-thermal radio emission?

Loo

Runacres

Blomme

2006

A&A

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We present a model for the non-thermal radio emission from presumably single O stars, in terms of synchrotron emission from relativistic electrons accelerated in wind-embedded shocks. These shocks are associated with an unstable, chaotic wind. The main improvement with respect to earlier models is the inclusion of the radial dependence of the shock velocity jump and compression ratio, based on one-dimensional time-dependent hydrodynamical simulations. The decrease of the velocity jump and the compression ratio as a function of radius produces a rapidly decreasing synchrotron emissivity. This effectively prohibits the models from reproducing the spectral shape of the observed non-thermal radio emission. We investigate a number of "escape routes" by which the hydrodynamical predictions might be reconciled with the radio observations. We find that the observed spectral shape can be reproduced by a slower decline of the compression ratio and the velocity jump, by the re-acceleration of electrons in many shocks or by adopting a lower mass-loss rate. However, none of these escape routes are physically plausible. In particular, re-acceleration by feeding an electron distribution through a number of shocks, is in contradiction with current hydrodynamical simulations. These hydrodynamical simulations have their limitations, most notably the use of one-dimensionality. At present, it is not feasible to perform two-dimensional simulations of the wind out to the distances required for synchrotron-emission models. Based on the current hydrodynamic models, we suspect that the observed non-thermal radio emission from O stars cannot be explained by wind-embedded shocks associated with the instability of the line-driving mechanism. The most likely alternative mechanism is synchrotron emission from colliding winds. That would imply that all O stars with non-thermal radio emission should be members of binary or multiple systems.

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Section: Introductionmentioning

confidence: 99%

Can single O stars produce non-thermal radio emission?

Loo

Runacres

Blomme

2006

A&A

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“…There are several numerical and analytical investigations of ion heating in the vicinity of the X-line and in the outflow region (e.g., Zelenyi et al 1990;Lottermoser et al 1998;Litvinenko 2003;Anastasiadis et al 2008;Zharkova & Agapitov 2009). The main problem of such models corresponds to the transient nature of the magnetic reconnection, where a X-line type magnetic field configuration with strong electric fields exists only at a limited time interval.…”

Section: Introductionmentioning

confidence: 99%

Preferential acceleration of heavy ions in the reconnection outflow region

Artemyev

Zimbardo

Ukhorskiy

et al. 2014

A&A

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Context. Many observations show that heating in the solar corona should be more effective for heavy ions than for protons. Moreover, the efficiency of particle heating also seems to be larger for a larger particle electric charge. The transient magnetic reconnection is one of the most natural mechanisms of charged particle acceleration in the solar corona. However, the role of this process in preferential acceleration of heavy ions has still yet to be investigated. Aims. In this paper, we consider charged particle acceleration in the reconnection outflow region. We investigate the dependence of efficiency of various mechanisms of particle acceleration on particle charge and mass. Methods. We take into account recent in situ spacecraft observations of the nonlinear magnetic waves that have originated in the magnetic reconnection. We use analytical estimates and test-particle trajectories to study resonant and nonresonant particle acceleration by these nonlinear waves. Results. We show that resonant acceleration of heavy ions by nonlinear magnetic waves in the reconnection outflow region is more effective for heavy ions and/or for ions with a larger electric charge. Nonresonant acceleration can be considered as a combination of particle reflections from the front of the nonlinear waves. Energy gain for a single reflection is proportional to the particle mass, while the maximum possible gain of energy corresponds to the classical betatron heating. Conclusions. Small-scale transient magnetic reconnections produce nonlinear magnetic waves propagating away from the reconnection region. These waves can effectively accelerate heavy ions in the solar corona via resonant and nonresonnat regimes of interactions. This mechanism of acceleration is more effective for ions with a larger mass and/or with a larger electric charge.

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Mass loss from hot massive stars

Puls

Vink

Najarro

2008

Astron Astrophys Rev

612

620

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Mass loss is a key process in the evolution of massive stars, and must be understood quantitatively to be successfully included in broader astrophysical applications. In this review, we discuss various aspects of radiation driven mass loss, both from the theoretical and the observational side. We focus on winds from OB-stars, with some excursions to the Luminous Blue Variables, Wolf- Rayet stars, A-supergiants and Central Stars of Planetary Nebulae. After reca- pitulating the 1-D, stationary standard model of line-driven wind, extensions accounting for rotation and magnetic fields are discussed. The relevance of the so-called bi-stability jump is outlined. We summarize diagnostical methods to infer wind properties from observations, and compare the results with theore- tical predictions, featuring the massloss-metallicity dependence. Subsequently, we concentrate on two urgent problems which challenge our present understanding of radiation driven winds: weak winds and wind- clumping. We discuss problems of measuring mass-loss rates from weak winds and the potential of NIR- spectroscopy. Wind-clumping has severe implications for the interpretation of observational diagnostics, as derived mass-loss rates can be overestimated by factors of 2 to 10 if clumping is ignored, and we describe ongoing attempts to allow for more uniform results. We point out that independent arguments from stellar evolution favor a moderate reduction of present- day mass-loss rates. We also consider larger scale wind structure, interpreted in terms of co-rotating interacting regions, and complete this review with a discussion of recent progress on the X-ray line emission from massive stars, highlighting as to how far the analysis of such X-ray line emission can give further clues regarding an adequate description of wind clumping. (Abridged abstract)Comment: Astronomy and Astrophysics Review (accepted

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Particle Acceleration by Magnetic Reconnection

Cited by 10 publications

References 38 publications

Can single O stars produce non-thermal radio emission?

Can single O stars produce non-thermal radio emission?

Preferential acceleration of heavy ions in the reconnection outflow region

Mass loss from hot massive stars

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