Diffusive shock acceleration and magnetic field amplification

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics

Abstract

Explosive events and supersonic flows are a feature of many of the most interesting objects in the universe. Explosions naturally produce shocks, and shocks naturally produce large numbers of very energetic particles such as those that arrive at the Earth as cosmic rays. These energetic particles are responsible for emission from long wavelength radio waves to extremely short wavelength gamma rays. This emission give us much of our information about astrophysical processes. We understand the general processes by which shocks accelerate energetic particles, but the detailed processes are less well understood. As the particle are accelerated they attempt to escape the shock, and in the process they set the surrounding medium into motion, which winds up the magnetic field lines and produces greatly increased magnetic field. The magnetic field deflects the trajectories of the accelerating particles and stops them escaping so they continue to be accelerated and eventually reach very high energies. Important breakthroughs in recent years have been x-ray observations which tell us that the magnetic field is stronger than previously thought and the development of a new theory of how accelerating particles produce the amplified field. The overall aim of the project is to investigate these processes using computer simulation. We will use a computer model to predict the strength of the magnetic field and the energy spectrum of the accelerated particles. We will then compare the computer predictions with a wide range of observations. This will help us to understand some of the most explosive and exotic phenoemna in the universe.

Publications

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Bell A (2013) Cosmic-ray acceleration and escape from supernova remnants in Monthly Notices of the Royal Astronomical Society

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Bell A (2013) Cosmic ray acceleration in Astroparticle Physics

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Bell A (2011) Cosmic ray acceleration at oblique shocks Cosmic ray acceleration at oblique shocks in Monthly Notices of the Royal Astronomical Society

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Bell A (2014) Particle Acceleration by Shocks in Supernova Remnants in Brazilian Journal of Physics

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Reville B (2013) Universal behaviour of shock precursors in the presence of efficient cosmic ray acceleration in Monthly Notices of the Royal Astronomical Society

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Reville B (2014) On the maximum energy of shock-accelerated cosmic rays at ultra-relativistic shocks in Monthly Notices of the Royal Astronomical Society

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Schure K (2012) Diffusive Shock Acceleration and Magnetic Field Amplification in Space Science Reviews

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Schure K (2014) From cosmic ray source to the Galactic pool in Monthly Notices of the Royal Astronomical Society

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Schure K (2013) Cosmic ray acceleration in young supernova remnants in Monthly Notices of the Royal Astronomical Society

 
Description We found that high energy particles, known as cosmic rays, can be accelerated to around 1PeV during the early months and years of the expansion of a supernova remnant. Energetic supernovae expanding into a dense medium of gas previously ejected from the star is the most suitable environment. We also found that the slope of the energy spectrum of cosmic rays accelerated by high velocity shocks can vary. we show that this matches the steep spectra found in very young supernova remnants expanding at high velocity.
Exploitation Route Our findings are now part of the common understanding of cosmic ray acceleration by shocks. The results concerning high velocity shocks are important for the question of whether mildly relativistic shocks are good accelerators of high energy cosmic rays.
Sectors Education,Culture, Heritage, Museums and Collections

 
Description Our findings represent a significant advance in our understanding of events in the universe at very high energy
First Year Of Impact 2000
Sector Education
Impact Types Cultural

 
Description Advanced Investigator Grant
Amount € 900,024 (EUR)
Funding ID CMR 247039 
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 05/2010 
End 04/2015
 
Description Lecture, Knutsford 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Type Of Presentation Keynote/Invited Speaker
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact 80 members of the public, mostly non-scientists, attended a presentation by myself on cosmic rays. The lively and exhausting open discussion lasted for 2 hours.

Nothing specific.
Year(s) Of Engagement Activity 2010