Transcript Solar Energetic Particles - Indian Institute of Astrophysics

Solar Energetic Particles
-acceleration and observations(Two approaches at the highest energy)
Takashi SAKO
Solar-Terrestrial Environment Laboratory,
Nagoya University, Japan
1st Asia Pacific School on International Heliophysical Year, 20-Dec-2007
Outline of the talk
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What are SEPs ?
How SEPs arrive ?
How SEPs are observed ?
What are SEPs ?
(What is SEP study?)
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Energetic particles (and photons)
coming from the Sun
But how energetic??
Energy of solar particles
• SEPs (and secondary particles)
are produced through eruptive,
non-thermal processes
• Far higher energy than other
solar particles
Energy of solar particles
• SEPs reach at relativistic energy
(kinetic energy = rest mass)
Solar particles & Cosmic particles
• SEPs are entrance to the cosmic
phenomenon
What are SEP studies ?
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Studies of the most energetic processes
around the sun through SEPs.
processes; acceleration, propagation,
neutral emission
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Prototype of the cosmic acceleration
Connection to the space weather
dose for astronauts, airplane crew
damage for the satellite electronics
How SEPs arrive ?
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Acceleration occurs somewhere,
sometime. (flare and/or CME)
Various approaches to the phenomena
Merit and demerit of approaches
Total understanding is the goal
Possible
Acceleration Site 1
Magnetic Reconnection @ flare
brems X by
accelerated
4 electrons
2
thermal X by
evaporated
5 electrons
1
Upward going plasma
(plasmoid)
Reconnection point
Downward going plasma
(reconnection jet)
2
3
Shock between jet &
solar atmosphere
5
photosphere
4
4
Possible Acceleration Site 2
Coronal Mass Ejection (CME)
SOHO LASCO
How SEPs arrive ?
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Acceleration occurs somewhere at
sometime. (flare vs. CME)
Various approaches to the phenomena
Merit and demerit of approaches
Total understanding is the goal
Approaches
• No direct particle from the
acceleration place.
- accelerated particles are affected
by magnetic field
- neutral particles need target to be
emitted.
• Approaches through various
paths are necessary.
What is cooked in the kitchen?
Charged
• Protons give high statistics.
• Other ions give the chemical
and temperature information of
the acceleration site.
• Significant effect from the
magnetic field
Neutral
• No effect of the magnetic field
• Lower flux because of 2ndary
• Emission process on the Sun
must be taken into account
How SEPs are observed ?
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Ground-based or Space
- only HE (>100MeV) ions and neutrons can be
observed at the ground.
- electrons, gamma-rays, chemical composition, charge
state are accessible only in space.
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Charged or Neutral
- neutral ; low flux but no magnetic effect
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Ions or Electrons
- ions ; higher energy, major component of CRs
How SEPs are observed ?
Observations of
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Highest energy (>100MeV) ions
(presumably protons) [ground-based]
Secondary neutrons by highest energy
protons [ground-based]
Secondary gamma-rays by highest energy
protons [space]
are introduced.
How SEPs are observed ?
(charged - ground level)
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Atmospheric attenuation - GLE
Neutron monitor, IGY
NM, network, magnetic spectrometer
Energy spectrum, highest energy,
acceleration limit
Attenuation - GLE
Interaction mean free path
; ~100 g/cm2
Sea level
Ground Level Enhancement ; 70 GLEs are recorded since 1942.
How SEPs are observed ?
(charged - ground level)
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Atmospheric attenuation
Neutron monitor, IGY
NM, network, magnetic spectrometer
Energy spectrum, highest energy,
acceleration limit
Neutron Monitor
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Installed over the world to monitor the longterm variation of the galactic cosmic-rays
International Geophysical Year, 1957-1958
International Quiet Sun Year, 1964-1965
Many of them are still active!!
Neutron Monitor
Neutron monitor
Proton or Neutron
BF3
Protons are
thermalized and
detected with a high
efficiency
Low energy resolution
thermal
neutron
B+n→Li+α+Q
NM network
Geomagnetic Effect
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Lorentz force depend on B, p and Z
R = pc/Ze ; rigidity
r ∝ R/B ; gyroradius
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Direction of the geomagnetic field
GLE strongly depends on the
observation site, energy spectrum and
anisotropy of SEPs.
⇒World-wide observations make an
excellent spectrometer
Spectrometer in Accelerator
GLE on 20-Jan-2005
20-Jan-2005
Energy spectrum of GLE
• Reach to 10 GeV
• Less effective acceleration at
higher energy
How SEPs are observed ?
(neutral - emission)
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Protons give rich observational data,
but require sophisticated analysis.
Neutrals give (statistically) poor data,
but require simple analysis.
Emission of neutral particles
Neutron Observations
Gamma-ray Observations
How SEPs are observed ?
(neutral - emission)
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Protons give rich observational data,
but require sophisticated analysis.
Neutrals give (statistically) poor data,
but require simple analysis.
Emission of neutral particles
Neutron Observations
Gamma-ray Observations
Emission in the atmosphere
trap
Injection of accelerated ions
(E-s, a(t), α/p ratio)
Loop length (L)
B∝Pδ
Solar atmosphere
model (composition, density)
Effective energy (gamma)
Effective energy (neutron)
How SEPs are observed ?
(neutron – ground level)
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No diffusion – important in timing info
Travel speed – energy measurement
NM observations
SNT
Event on 7-Sep-2005
Neutron energy – speed
flux
10 min delay
from light
1 min delay
from light
Harder -> Faster
Softer -> Slower
100MeV
1GeV
energy
Neutron Rate (Arbitrary)
Neutron spectrum - hardness
10 min
Time (second)
* Time profile of the Neutron Monitor counting rate
is sensitive to the neutron spectrum.
* Good indicator of the spectrum, but…
10 min
Power law index; 2.5
Continuous emission; 300sec
NM counting rate (arbitrary)
NM counting rate (arbitrary)
NM observation
10 min
Power law index; 4.0
Instantaneous emission
7 Sep 2005, NM
100MeV
* NM detected neutron signal at 7 Sep 2005
* Fast emission with power-law spectrum can not explain tail
* Is it long emission or high flux of low energy neutron below
100MeV???
Solar Neutron Telescope
Energy measurement
Direction measurement
Low latitude, high altitude
neutron
proton
SNT Network
7 Sep 2005, SNT
* Low energy (delayed) neutron can not explain the tail
* Emission must be continuous
How SEPs are observed ?
(gamma-ray - space)
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No diffusion – important in timing info
Travel with speed of light
Lower effective energy
Sometimes clear signal, but not other
times
Imaging possibility
Gamma-ray spectrum
Gamma-ray profile
* Precise measurement
* Low effective energy
Gamma-ray image
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Interesting but small example
Summary
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Single/multiple observations and
analyses give partial info of each event
Ideal observation and total analysis are
expected; GLE, neutron with energy,
gamma-ray, with high statistics
Need also composition, charge state,
electrons, radio, etc
Summary
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SEPs are entrance to learn energetic
phenomena in the universe.
SEPs are one of the important subjects in the
Space Weather.
Various approaches give us independent,
partial information of the SEPs.
Total understanding of SEPs through rich
observations is waited.
Active efforts in experiment and theory in
progress.
Hillas Diagram