Diapositiva 1

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Ia Giornata delle Interazioni Spazio-Geospazio
HIGH ENERGY EMISSION FROM SOLAR FLARES
Giulia Iafrate - 8 maggio 2007
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OVERVIEW

• WHY WE STUDY SOLAR FLARES
• PHYSICS OF SOLAR FLARES
• FLARE SPECTRUM
• PRODUCTS OF INTERACTIONS
• HIGH ENERGY OBSERVABLE EMISSION
• SPECTRUM OF THE 23 JULY 2002 FLARE
• THE QUIET SUN

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SOLAR FLARE BASICS

• sudden release of energy
  stored in the magnetic
  field (up to 1025 J)
  
• take place in the corona
• and chromosphere
• large flares occur only at
• solar maximum
• heat plasma and accelerate electrons, protons and
  heavier nuclei
• produce electromagnetic radiation

SOHO
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WHY STUDY SOLAR FLARES?

• the most energetic phenomena in the Solar System
• not well known and cannot be predicted
• can have dangerous and distruptive conseguences
  in space and on the Earth
• the Sun is closer and more easily observed than
  the other sites in the Universe (pulsars, AGN,
  GRB, black holes...) where the same high energy
  processes occur

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WHY STUDY X- and ?-RAY FLARES?

• from X-ray and ?-ray emission we can investigate
• what is the relative amount of energy injected
  directly into plasma heating vs. particle
  acceleration
• what are the acceleration mechanisms involved
• where these processes take place
• what is the total magnetic energy released

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WHERE DO FLARES ORIGINATE?

• in magnetic structures called loops ( 107 - 108
  m)
• loops are the closed magnetic field lines
  extending from the surface to the corona
  
• loops connect active
• regions (sunspots) and
• trap charged particles
• flares heat up the plasma
• to higher temperatures,
• up to 40 MK

earth
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MAGNETIC RECONNECTION
an efficient mechanism to release a large amount
of magnetic energy in a short time
flare
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PRODUCTS OF INTERACTIONS

• electrons X-ray and ?-ray bremsstrahlung
• ions excited nuclei
• ? prompt ?-ray line radiation
• radioactive nuclei
• ? delayed ?-ray line radiation
• neutrons ? escape into space
• ? capture on H ? D ?(2.223 MeV)
• p, p-, p0 ? ? (continuum, 511 keV line
• and e-e bremsstrahlung)

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OBSERVABLE EMISSION

• X-ray and ?-ray bremsstrahlung
• positron annihilation line
• escaping neutrons
• neutron capture line
• nuclear de-excitation ?-ray lines
• pion decay emission

THE LINES ARE DOPPLER BROADENED AND SHIFTED
BECAUSE OF THE HIGH VELOCITIES OF THE NUCLEI AS
THEY DECAY AND EMIT THE ?-RAYS
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BREMSSTRAHLUNG

• soft X-rays bremsstrahlung by hot ambient
• plasma with at least 107 K (thermal brems.)
• hard X-rays thick target bremsstrahlung
• electrons previously accelerated to higher
• energies
• BREMSSTRAHLUNG SPECTRUM
• CAN EXTEND UP INTO
• THE ?-RAY RANGE
• WE CAN DETERMINE WHERE
• AND HOW MANY ELECTRONS
• ARE ACCELERATED AND TO
• WHAT ENERGIES

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511 keV e-e ANNIHILATION LINE
positron production ß decay p ? n e
? pions p ? µ ? ? e ?
? other sources ? ? ? e- e

positron annihilation direct annihilation e
e- ? 2?(511 keV) gt SINGLE LINE positronium
formation e e- ? Ps h? e 1H ? Ps p (
) Ps(triplet spin state)? 3?(lt 511 keV) gt
CONTINUUM
CHARGE EXCHANGE
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2.223 MeV NEUTRON CAPTURE LINE
n H ? D ?(2.223 MeV) neutrons thermalize in
the dense photosphere (T6000 K) before
capture - line width due to thermal Doppler
broadening is very small (lt 10 eV) - ?-rays
delayed of 100s after neutrons are produced
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DE-EXCIT. ?-RAY LINES (0.5 - 8 MeV)
- narrow lines collisions of accelerated protons
or a-particles with chromospheric nuclei -
broad lines collisions of accelerated C and
heavier nuclei with ambient H and a-particles
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DE-EXCITATION LINE SPECTRUM

NARROW LINES
BROAD LINES
24Mg
20Ne
28Si
12C
16O
56Fe
Fortran code by R. Ramaty, B.J. Murphy and B.
Kozlovsky
ENTIRE SPECTRUM
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PION DECAY EMISSION
total
p0 ? 2? ?-rays peak at 67.5 MeV
p0 p bremss. p- bremss. p annihil.
p ? µ ? e ?(511 keV) from ee-
annihilation continuum emission via
bremsstrahlung from both e- and e
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LONG DURATION ?-RAY FLARES

• ?-ray (and/or neutron) emission
• (gt 1 MeV) present well beyond the impulsive
  phase
• particles accelerated in the
• impulsive phase and trapped
• at the Sun and/or
• particles continuosly accelerated
• NOT TO BE CONFUSED WITH
• ?-RAY FLARES

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23 JULY 2002 FLARE SPECTRUM
30 keV
0.5 MeV
nuclear de-excitation lines (accelerated
ions)
thick target bremsstrahlung (accelerated
electrons)
thermal plasma
X4.8-class flare of 23 July 2002
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23 JULY 2002 FLARE SPECTRUM
ee- annihilation (511 keV)
20Ne (3.334 MeV)
20Ne (1.633 MeV)
neutron capture (2.223 MeV)
thick target bremsstrahlung
X4.8-class flare of 23 July 2002 (0.3 - 7 MeV)
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THE QUIET SUN IC
the heliosphere is filled with - GCR
electrons (isotropic) - solar photons (radial
angular distribution)
targets for inverse compton scattering by GCR
electrons
the heliosphere is a diffuse source of ?-rays
with a broad angular distribution
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MODULATION
IC spectrum shows strong dependence on the
modulation level ? variation of ?-ray flux over
the solar cycle
gt100 MeV
IS spectrum
Current EGRB
gt1 GeV
Modulated 500 MV
Modulated 1000 MV
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EGRET RESULTS (1991 FLARE)

• the data in the sun-centred system are fitted
  using a multi-parameter
• likelihood fitting technique with 6 components
  and 4 free parameters
• 1. solar disk
• 2. solar extended inverse-Compton
• 3. 3C279
• 4. moon
• 5. other 3EG sources
• 6. background
• convolved with the energy-dependent EGRET PSF

flux map gt 100 MeV Sun centered
20 fit region
SOLAR DISK IC
MOON 3C279
TOTAL
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FINE