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Lecture 2 What happens in the region of the ‘knee’ in the spectrum? Speculation

Dive into the region of the cosmic ray spectrum around the ‘knee’ with discussions on measurements, speculations, and the importance of understanding Hadronic Physics. Explore the mysteries of the Crab Nebula and the challenges in detecting elusive gamma-rays.

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Lecture 2 What happens in the region of the ‘knee’ in the spectrum? Speculation

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  1. Lecture 2 • What happens in the region of the ‘knee’ in the spectrum? • Speculation • Measurements by the KASCADE project • Ultra High Energy Cosmic Rays • Why? • How? (Volcano Ranch and Haverah Park) • AGASA and HiRes results

  2. The Crab Nebula: remnant of star that exploded in 1054

  3. Expected shape of spectrum: Differential index a ~ 2.1 for diffusive shock acceleration aobserved ~ 2.7; asource ~2.1; Da~ 0.6 tesc(E) ~ E-0.6 c tesc Tdisk ~100 TeV Isotropy problem Emax ~ bshock Ze x B x Rshock  Emax ~ Z x 100 TeV with exponential cutoff of each component But spectrum continues to higher energy:  Emax problem Expect p + gas  g (TeV) for certain SNR Need nearby target as shown in picture from Nature (April 02) Interpretation uncertain; see Enomoto et al., Aharonian (Nature); Reimer et al., astro-ph/0205256  Problem of elusive p0g-rays Problems of simplest SNR shock model

  4. Knee Importance of knowing the Hadronic Physics Ankle air-showers >1019 eV 1 km-2 sr-1 year-1 after Gaisser

  5. 1 component: a = 2.7, Emax = Z x 30 TeV; or Emax = Z x 1 PeV Total protons Fe helium CNO Mg… 3 components a=2.7 a=2.4 Speculation on the ‘knee’ KASCADE (Karlsruhe) Designed to attack this problem Crucial to know the mass

  6. Jörg R Hörandel

  7. p p0 p- n g p p+ e- g e+ e+ µ- e- p+ p0 g p n g p- µ+ p0 p- n g g p n e+ p e- p- µ- e- e+ e- KArlsruhe Shower Core and Array DEtector Simultaneous measurement of electromagnetic, muonic, hadronic shower components Concept of Gerd Schatz T. Antoni et al, Nucl. Instr. & Meth. A 513 (2004) 490

  8. At the energies studied by KASCADE, models are required to extract mass and energy of primary

  9. SYBILL and QGSjet are the favoured models amongst cosmic ray physicists at the moment In both models free parameters are adjusted to fit p-p and p-pbar data at accelerators Differences: Assumptions about the spatial distribution of partons in protons and pions Eikonal model Simple view: QGSjet is more efficient in muon production than SIBYLL For details see Alvarez-Muñiz et al. astro-ph/0205302

  10. The growth of Nμwith Eo is less-than-linear (β < 1). Lower energy showers are more “efficient” in muon production This is why Fe primaries make more muons than protons do (superposition model: 56 showers each with E = Ep/56) β depends on the (logarithmic) ratio of charged to neutral pions

  11. KASCADE : Astroparticle Physics 16 373 2002 • KNEE CAUSED BY • DECREASING FLUX OF LIGHT ELEMENTS

  12. two hadronic interaction models: CORSIKA 6.018/GHEISHA 2002 - QGSJET 01 - SIBYLL 2.1 All-particle energy spectrum T. Antoni et al., Astropart. Phys. (2005)

  13. KASCADE: Energy spectra for individual elemental groups T. Antoni et al., Astropart. Phys. (2005)

  14. KASCADE: Energy spectra for individual elemental groups T. Antoni et al., Astropart. Phys. (2005)

  15. KASCADE: Energy spectra for individual elemental groups c2 distribution c2 distribution ! ! QGSJET SIBYLL ? And we will find that energy spectrum can be LESS model-independent at the highest energies But – Z-dependence is rather clear T. Antoni et al., Astropart. Phys. (2005)

  16. Now to the Highest Energy Cosmic Rays: • The interest in Ultra High Energy Cosmic Rays • Methods of Detection • - The Pierre Auger Observatory • To-morrow: New Auger Results • Arrival Directions • Energy Spectrum • Mass Composition • Summary

  17. Why study Ultra-High Energy Cosmic Rays? - no idea of their origin - how to accelerate to 1020eV? - steepening of spectrum at highest energies? PROPAGATION EFFECTS or SOURCES? Difficulties:Above 1019 eV the rate is ~ 1 km-2 per year - energies are hard to measure - mass spectrum is unknown - no anisotropies established

  18. Acceleration region ~ Larmor radius of accelerating particle B, must be sufficiently weak to limit synchrotron losses. Analysis (Greisen) shows that the energy of the magnetic field grows as 5, where  is the Lorentz factor of the particle. For 1020 eV, EB >> 1057 ergs and B < 0.1 gauss. Such putative cosmic ray sources are also likely to be strong radio emitters with radio power >> 1041 ergs s-1, unless protons or heavier nuclei are being accelerated and electrons are not. So acceleration of the most energetic cosmic rays will take place in rare but well-known objects mostly very far from earth.

  19. Electromagnetic Acceleration • Synchrotron Acceleration • Emax = ZeBRc • Single Shot Acceleration • Emax = ZeBRc • Diffusive Shock Acceleration • Emax = kZeBRc, with k<1 • Shocks in AGNs, near Black Holes……

  20. Hillas 1984 ARA&A B vs R Magnetars? GRBs?

  21. Preprint: “END TO THE COSMIC-RAY SPECTRUM” Initially, CMB temperature was ~ 3 K: later 2.73 K – unfortunately not 3.3 K ….in preparation are doomed to failure.

  22. Spectrum shape: • E = 2 Γε2.7 K (for head-on collision) • Steepening above 4 x 1019 eV? (GZK-effect) • γ2.7 K+ p  Δ+  n + π+ or p + π- (CMB well- • known) • or • γIR+ A  (A – 1) + n (IR background poorly • known) • Also γ + γradio e+ + e-(but 100 MHz background • unknown)

  23. Existence of particles above GZK-steepening would imply that sources are close (< 50 Mpc) IF particles are protons, the deflections are small enough above ~ 4 x 1019 eV that point sources should be seen So, find: - energy spectrum - arrival direction distribution - mass composition But rate at 1020 eV is ~ 1 per km2 per century

  24. Cronin 1992 p + 2.7K +  p + 0 or n + +

  25. Top Down Mechanisms • Developed because many phenomenologists believe that • there is evidence for protons at high energy • Topological defects: • Cosmic strings and necklaces • Decay of monopoles • Manifestations of Super-heavy relic particles • High-energy protons would be an important tools to probe • ideas about new physics

  26. Shower Detection Methods ~1° Nitrogen fluorescence 300 – 400 nm Fluorescence in UV → OR Array of water-Cherenkov or scintillation detectors 11

  27. The Volcano Ranch Array: Linsley (1963) - the pioneer Energy ~ 1020 eV Pre-GZK prediction

  28. The shower array at Haverah Park. The area enclosed was ~12 km2. Each point in in the diagram represents a water tank. At the points A1 - A4 the total tank areas were 34 m2.

  29. Event with energy of ~ 8 x 1019 eV, well above GZK steepening recorded with water-Cherenkov detectors at Haverah Park (UK) Haverah Park (1967 – 1987) with 12 km2 and ~ 250 water-tanks

  30. Atank was opened at the ‘end of project’ party on 31 July 1987. The water shown had been in the tank for 25 years but was quite drinkable!

  31. AGASAAkeno Giant Air Shower Array100 km2 Closed in December 2003 ~1600 km2 sr years 111 scintillators + 27 muon det.

  32. AGASA: 230 EeV To estimate primary energy requires assumptions about models and mass

  33. x 1010 Calorimetric Energy Estimate 3 x 1020 eV !!! Successor project: HiRes

  34. HiRes: detector of fluorescence light

  35. Surface Detectors Energy Estimates are model and mass dependent Recent reanalysis has reduced number > 1020 eV to 6 events Takeda et al. ApP 2003

  36. Fluorescence Detectors The HiRes group have yet to release a stereo spectrum. Recent paper: astro-ph/ 0703099 will be discussed later

  37. The Pierre Auger Collaboration Santiago de Compostela (2001) Complutense de Madrid Alcalá Granada Valencia Aim: To measure properties of UHECR with unprecedented statistics and precision – necessary even if no disagreement

  38. Some History: August 1991: First idea – Jim Cronin and AAW April 1992: First International meeting to float the idea Jan – June 1995: Design study and site searches November 1995: Southern site selection November 1996: Northern site selection May 1997: SAGENAP approval 17 March 1999: Ground Breaking Ceremony January 2004: Data taking started

  39. For the first eighteen months or so, Jim and I were in favour of using only a ground array. This was probably our worst piece of misjudgement throughout the whole enterprise. Situation changed after Tokyo Workshop in Sept 1993 –

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