Prompt acceleration of ? 30 MeV per nucleon ions in solar flares

Melrose, D. B.

doi:10.1007/bf00211959

Cited by 25 publications

(3 citation statements)

References 43 publications

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“…4.3.3 is subject to an 'injection problem' as it comes down to the lightest nuclei 12 , i.e., to accelerate those particle species beyond the energy 0.5 m υ 2 A , seeds are required. Reconnection might provide those seeds (Melrose 1983;Drury 2012), as no minimum energy threshold for thermal particles is required to be accelerated by magnetic reconnection.…”

Section: Christiansenmentioning

confidence: 99%

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Wykes

Croston

Hardcastle

et al. 2013

A&A

127

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Observations of the FR I radio galaxy Centaurus A in radio, X-ray, and gamma-ray bands provide evidence for lepton acceleration up to several TeV and clues about hadron acceleration to tens of EeV. Synthesising the available observational constraints on the physical conditions and particle content in the jets, inner lobes and giant lobes of Centaurus A, we aim to evaluate its feasibility as an ultra-high-energy cosmic-ray source. We apply several methods of determining jet power and affirm the consistency of various power estimates of ∼1 × 10 43 erg s −1 . Employing scaling relations based on previous results for 3C 31, we estimate particle number densities in the jets, encompassing available radio through X-ray observations. Our model is compatible with the jets ingesting ∼3 × 10 21 g s −1 of matter via external entrainment from hot gas and ∼7 × 10 22 g s −1 via internal entrainment from jet-contained stars. This leads to an imbalance between the internal lobe pressure available from radiating particles and magnetic field, and our derived external pressure. Based on knowledge of the external environments of other FR I sources, we estimate the thermal pressure in the giant lobes as 1.5 × 10 −12 dyn cm −2 , from which we deduce a lower limit to the temperature of ∼1.6 × 10 8 K. Using dynamical and buoyancy arguments, we infer ∼440−645 Myr and ∼560 Myr as the sound-crossing and buoyancy ages of the giant lobes respectively, inconsistent with their spectral ages. We re-investigate the feasibility of particle acceleration via stochastic processes in the lobes, placing new constraints on the energetics and on turbulent input to the lobes. The same "very hot" temperatures that allow self-consistency between the entrainment calculations and the missing pressure also allow stochastic UHECR acceleration models to work.

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Section: Christiansenmentioning

confidence: 99%

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Wykes

Croston

Hardcastle

et al. 2013

A&A

127

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“…For the June 7, 1980, flare for which 6-2.8, shock acceleration could only explain delays of 3.5 s or greater, even allowing for multiple encounters with one shock. Thus another mechanism such as stochastic acceleration by hydromagnetic turblence [Melrose, 1983] or other wave acceleration processes must be invoked to explain the observed < 2-s delay for this flare.…”

Section: Discussionmentioning

confidence: 97%

Shock formation time and the viability of prompt MeV proton shock acceleration in solar flares

Smith¹,

Brecht²

1985

J. Geophys. Res.

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A critical analysis is made of a proposed mechanism to explain the ≲2‐ to 100‐s delays observed in some flares between γ rays due to several MeV protons and hard X rays due to ∼100‐keV electrons. The proposed mechanism is first‐order Fermi acceleration of protons bouncing between two shocks formed by the electrons causing the hard X rays. For the maximum possible flux for stable beam propagation the shock formation time is found to be ≳2 s and the shock velocity ≲1800 km s−1. The mechanism as proposed produces protons which gain only ∼3 MeV before they are transmitted through the shocks. The mechanism will work with additional pitch angle scattering, which also raises the possibility of multiple encounters with a single shock, a case not analyzed. For this reason the final energy gains of the proposed mechanism may be altered. The times during which this type of shock acceleration could be important and thus the range of observed delays which could be explained are given for a range of loop lengths and injected electron spectra. Alternate possibilities such as stochastic acceleration by hydromagnetic turbulence must be invoked to explain the shortest delays associated with this prompt proton acceleration.

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“…Several specific mechanisms for the prompt acceleration of such ions were discussed by, e.g., Melrose (1983), Bai and Dennis (1985), Ellison and Ramaty (1985), Decker and Vlahos (1986), Droge and Schlickeiser (1986), Ohsawa and Sakai (1988), Brecht (1988, 1989a,b). The most notable result of these various investigations is that a variety of different acceleration mechanisms can be effective on the observed short time scale.…”

Section: Prompt Acceleration Of Ionsmentioning

confidence: 99%

Particle Acceleration Processes in the Solar Corona

Melrose¹

1990

Aust. J. Phys.

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Theoretical ideas on particle acceleration associated with solar flares are reviewed. A historical outline is used to introduce the various acceleration mechanisms. These are stochastic acceleration in its various forms, diffusive acceleration at shock fronts, shock drift acceleration, resonant acceleration, acceleration during magnetic reconnection and acceleration by parallel electric fields in double layers or electrostatic shocks. Particular emphasis is placed on so-called first phase acceleration of electrons in solar flares, which is conventionally attributed to bulk energisation of electrons (Ramaty et al. 1980). There is no widely accepted theory for bulk energisation, which may be regarded as an enhanced form of heating. Ideas on bulk energisation are discussed critically. It is argued that the dissipation cannot be due to classical resistivity and involves anomalous resistivity or hyperresistivity, e.g., in multiple double layers. The dissipation must occur in very many localised regions. Bulk energisation due to magnetic reconnection is discussed briefly. A model for bulk energisation due to the continual formation and decay of weak double layers is outlined

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Prompt acceleration of ? 30 MeV per nucleon ions in solar flares

Cited by 25 publications

References 43 publications

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Shock formation time and the viability of prompt MeV proton shock acceleration in solar flares

Particle Acceleration Processes in the Solar Corona

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