1. Solar Energetic Particles -acceleration and observations- (Two approaches at the highest energy) Takashi SAKO Solar-Terrestrial Environment Laboratory, Nagoya University, Japan 1 st Asia Pacific School on International Heliophysical Year, 20-Dec-2007

2. Outline of the talk What are SEPs ? How SEPs arrive ? How SEPs are observed ?

3. What are SEPs ? (What is SEP study?) Energetic particles (and photons) coming from the Sun But how energetic??

4. Energy of solar particles SEPs (and secondary particles) are produced through eruptive, non-thermal processes Far higher energy than other solar particles

5. Energy of solar particles SEPs reach at relativistic energy (kinetic energy = rest mass)

6. Solar particles & Cosmic particles SEPs are entrance to the cosmic phenomenon

7. What are SEP studies ? Studies of the most energetic processes around the sun through SEPs. processes; acceleration, propagation, neutral emission Prototype of the cosmic acceleration Connection to the space weather dose for astronauts, airplane crew damage for the satellite electronics

8. How SEPs arrive ? Acceleration occurs somewhere, sometime. (flare and/or CME) Various approaches to the phenomena Merit and demerit of approaches Total understanding is the goal

9. Possible Acceleration Site 1 Reconnection point Upward going plasma (plasmoid) Downward going plasma (reconnection jet) Shock between jet & solar atmosphere photosphere brems X by accelerated electrons thermal X by evaporated electrons 1 2 2 3 44 5 5 4 Magnetic Reconnection @ flare

10. Possible Acceleration Site 2 Coronal Mass Ejection (CME) SOHO LASCO

11. How SEPs arrive ? Acceleration occurs somewhere at sometime. (flare vs. CME) Various approaches to the phenomena Merit and demerit of approaches Total understanding is the goal

12. 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. Approaches

13. What is cooked in the kitchen?

14. Protons give high statistics. Other ions give the chemical and temperature information of the acceleration site. Significant effect from the magnetic field Charged

15. Neutral No effect of the magnetic field Lower flux because of 2ndary Emission process on the Sun must be taken into account

16. How SEPs are observed ? 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. Charged or Neutral - neutral ; low flux but no magnetic effect Ions or Electrons - ions ; higher energy, major component of CRs

17. How SEPs are observed ? Highest energy (>100MeV) ions (presumably protons) [ground-based] Secondary neutrons by highest energy protons [ground-based] Secondary gamma-rays by highest energy protons [space] Observations of are introduced.

18. How SEPs are observed ? (charged - ground level) Atmospheric attenuation - GLE Neutron monitor, IGY NM, network, magnetic spectrometer Energy spectrum, highest energy, acceleration limit

19. Attenuation - GLE Interaction mean free path ; ~100 g/cm2 Sea level Ground Level Enhancement ; 70 GLEs are recorded since 1942.

20. How SEPs are observed ? (charged - ground level) Atmospheric attenuation Neutron monitor, IGY NM, network, magnetic spectrometer Energy spectrum, highest energy, acceleration limit

21. Neutron Monitor Installed over the world to monitor the long- term variation of the galactic cosmic-rays International Geophysical Year, 1957-1958 International Quiet Sun Year, 1964-1965 Many of them are still active!!

22. Neutron Monitor

23. Neutron monitor BF 3 Proton or Neutron thermal neutron B+n → Li+α+Q Protons are thermalized and detected with a high efficiency Low energy resolution

24. NM network

25. Geomagnetic Effect Lorentz force depend on B, p and Z R = pc/Ze ; rigidity r ∝ R/B ; gyroradius 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

26. Spectrometer in Accelerator

27. GLE on 20-Jan-2005 20-Jan-2005

28. Energy spectrum of GLE Reach to 10 GeV Less effective acceleration at higher energy

29. How SEPs are observed ? (neutral - emission) 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

30. How SEPs are observed ? (neutral - emission) 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

31. Emission in the atmosphere

32. Injection of accelerated ions (E -s, a(t), α/p ratio) B∝PδB∝Pδ Loop length (L) Solar atmosphere model (composition, density) trap

33. Effective energy (gamma)

34. Effective energy (neutron)

35. How SEPs are observed ? (neutron – ground level) No diffusion – important in timing info Travel speed – energy measurement NM observations SNT Event on 7-Sep-2005

36. Neutron energy – speed 100MeV 1GeV 1 min delay from light 10 min delay from light flux energy Harder -> Faster Softer -> Slower

37. Neutron spectrum - hardness Neutron Rate (Arbitrary) Time (second) 10 min * Time profile of the Neutron Monitor counting rate is sensitive to the neutron spectrum. * Good indicator of the spectrum, but…

38. NM observation Power law index; 2.5 Continuous emission; 300sec Power law index; 4.0 Instantaneous emission NM counting rate (arbitrary) 10 min NM counting rate (arbitrary) 10 min

39. 7 Sep 2005, NM * 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??? 100MeV

40. Solar Neutron Telescope Energy measurement Direction measurement Low latitude, high altitude neutron proton

41. SNT Network

42. 7 Sep 2005, SNT * Low energy (delayed) neutron can not explain the tail * Emission must be continuous

43. How SEPs are observed ? (gamma-ray - space) No diffusion – important in timing info Travel with speed of light Lower effective energy Sometimes clear signal, but not other times Imaging possibility

44. Gamma-ray spectrum

45. Gamma-ray profile * Precise measurement * Low effective energy

46. Gamma-ray image Interesting but small example

47. Summary 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

48. Summary 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.

49. Hillas Diagram