The Sun as a Particle Accelerator

S.A. Matthews1, D.R. Williams1, L.M. Green1,

L. Fletcher2, E. Kontar2, I. Hannah2, A.L. MacKinnon2,

V. Nakariakov3, D. Tsiklauri4, V.V. Zharkova5,

P. Browning6, R.A. Harrison7, M. Mathioudakis8, C. Parnell9

1UCL Mullard Space Science Laboratory2University of Glasgow3University of Warwick4Queen Mary University5University of Bradford6University of Manchester7STFC Rutherford Appleton Laboratory8Queen’s University Belfast9St Andrews University

Øleroset et al. 2001

• Fundamental process for energising plasma in a host of cosmic settings:

– Flares in main-sequence stars

– solar wind

– accretion disks

– T Tauri stars (star formation)

– magnetosphere

– + ...

• Gap in our knowledge:

– We have empirical evidence about e- acceleration, but...

– we still know almost nothing about ion acceleration!

– Lacking crucial data in windows yet to be opened up.

Acceleration through Collisionless Reconnection

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Hurford et al. 2006

γ-rays(protons, ions)

X-rays (electrons)

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• We know magnetic fields play a role,...

• But, how and where is acceleration triggered?

• Why is acceleration so efficient?

• Are ions always accelerated?

– Are they accelerated in different places than e-?

– Or are they just accelerated differently?

• Can we trace them from cradle to grave?

Magnetic structuresreorganise

Energetic particles hit

Particle Acceleration

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Particle Acceleration

• Huge amounts of energy are carried by particles, often at ultra-relativistic velocities.

• What is the nature of the acceleration process?

– Stochastic acceleration (waves, turbulence) ;

– Direct electric fields (e.g. reconnection Ē) ;

– Fermi acceleration at shocks (first- and second-order)?

– ion vs electron vs positron acceleration

• And what carries the energy?

– how much is carried by ions, electrons, ...neutrals;

– π0, π± decay gives clues to ions’ high energy cut-off

• By understanding how and where this energy is deposited on our closest star, we can build a solid foundation for a physical understanding of astrophysical plasmas.

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Kaufmann et al. (2004)

• Particle-heated chromosphere is also expected to radiate in THz range– feedback between non-thermal

particles, thermal populations and, magnetic fluctuations and structures is poorly understood

• Recent sub-THz observations give tantalising clues to e- / e+ acceleration

– Gyrosynchrotron emission?

– Shape of the spectrum into the THz domain is key to discriminating the mechanism(s) responsible for this acceleration.

?

Our atmosphereis opaque!

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Tracing the process

• Thermal continuum emission from the chromosphere when particles hit• Achieve upper limits on the initial accelerated particle energies

– First measurements of solar flares in THz (35 and 150 μm... and beyond) from space.

• Probe the very highest energy particles (protons and ions) that are produced by the Sun

– HXR/gamma-ray spectrometry at highest energies attained with a solar instrument (10 keV – 600 MeV).

• Look for the sources and sinks of energetic particles– At thermal and non-thermal energies

– Which field lines do the particles stream down?

– Direct HXR imaging up to ~70 keV (focussing optics).– High resolution (0.1”) SXR imaging up to 20 keV

• Find where the particles end up in the chromosphere.– What are the magnetic structures, low down, associated with these sites?

– How do they guide particles and determine the coronal magnetic field?

– High resolution chromospheric imaging and magnetic field information

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Concept – Baseline PayloadInstrumentComparison

εmin or λmax εmax or λmin ΔΕ or Δλ Δs Δt

1. THz Imager(sub-mm)

0.9 Thz(350 µm)

8.5 THz(35 µm)

multiple bands 50” 100 ms

No comparison!

2. High-ε Spectrometer 10 keV 600 MeV 2 keV(662 keV)

32 ms – 1 s

RHESSI 3 keV 30 MeV 1 – 10 keV 2.3” to 36”

< 10 ms to 4 s

3. Focusing X-ray Imager(Direct Imaging)

~3 keV 70 keV ~1 keV 15” ~0.1 s

Solar Orbiter/STIX 4 keV 150 keV 1 – 15 keV 7” 1 – 5 s

4. Hi-Res X-ray Imager(smart X-ray optics)

~1 keV 20 keV 0.5 keV 0.1” 0.1 s

Hinode/XRT 0.06 keV 6.2 keV multiple bands 2” ~60 s

5. Lyman α imager 1216 Å 1” 0.2 – 20 s

Solar Orbiter/EUI 1216 Å equivalent 0.3” <1 – 100 s

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Platform Requirements

Orbit Sun synchronous (e.g., TRACE, RHESSI, Hinode)

Pointing Accuracy: 1 – 5” Stability: better than 0.1”

Telemetry ~ 50 Gb day-1

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Scientific Base of Interest (UK)

• UK:

• UCL Mullard Space Science Laboratory

• University of Glasgow

• University of Warwick

• Queen Mary University

• University of Bradford

• University of Manchester

• STFC Rutherford Appleton Laboratory

• Queen’s University Belfast

• University of Central Lancashire

• University of St Andrews

• + ...

• Europe

• Observatoire de Paris à Meudon

• + ...

• This is a proto-consortium, and we welcome new involvement!

Key UK academic institutes have been involved in developing this concept

In a nutshell

• Novel science with direct application to particle acceleration across physics.

• Strong support from a large cross-section of the community, in UK and in Europe

• Builds directly on key UK science strengths, technology development and heritage.