1. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Outstanding problems in Particle Astrophysics Cosmic-ray propagation Acceleration Sources

2. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Spectrometers (  A = 1 resolution, good E resolution) Calorimeters (less good resolution) Direct measurements Air showers

3. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser A fundamental result Excess of Li, Be, B from fragmentation of C, O Spallation  plus  ISM give dwell time of nuclei –Find  ~ 3 x 10 6 yrs –c  ~ Mpc >> size of galactic disk (kpc) –Suggests diffusion in turbulent ISM plasma –Predictions for  -rays, positrons and antiprotons follow

4. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Diffuse galactic secondaries p + gas   0     antiprotons            e   Hard  -spectrum suggests some contribution from collisions at sources BESS antiprotons, 1997, ’99, ’00. Fully consistent with secondary production by collisions in ISM followed by solar modulation varying with solar cycle Phys.Rev.Lett. 88 (2002) 051101

5. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Electrons & positrons Primary electrons: –spectrum steeper than p –energy loss at high E e + as secondaries: –5-10% fraction –level consistent with p + gas   +   +  e + Bump in charge ratio: –primary e + ? … or –glitch in e - spectrum?

6. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Energy-dependence of secondary/primary cosmic-ray nuclei B/C ~ E -0.6 Observed spectrum: –  (E) = dN/dE ~ K E -2.7 Interpretation: –Propagation depends on E –  (E) ~ E -0.6 –  (E) ~ Q(E) x  (E) x (c/4  ) Implication: –Source spectrum Q(E) ~ E -2.1

7. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Energetics of cosmic rays Total local energy density: –(4  /c) ∫ E  (E) dE ~ 10 -12 erg/cm 3 ~ B 2 / 8  Power needed: (4  /c) ∫ E  (E) /  esc (E) dE galactic  esc ~ 10 7 E -0.6 yrs Power ~ 10 -26 erg/cm 3 s Supernova power: 10 51 erg per SN ~3 SN per century in disk ~ 10 -25 erg/cm 3 s SN model of galactic CR Power spectrum from shock acceleration, propagation Spectral Energy Distribution (linear plot shows most E < 100 GeV) (4  /c) E  (E) = local differential CR energy density

8. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Solar flare shock acceleration Coronal mass ejection 09 Mar 2000 09 Mar 2000

9. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser SOHO/ LASCO CME of 06-Nov 1997

10. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Supernova progenitor SN ejecta Shocked ISM Supernova blast wave acceleration Unshocked ISM SNR expands into ISM with velocity V~ 10 4 km/s. Drives forward shock at 4/3 V Forward shock u 1 ~ 4/3 V Particle with E 1 E 2 =  E 1 Contact discontinuity, V T SN ~ 1000 yrs before slowdown E max ~ Z x 100 TeV

11. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Problems of simplest SNR shock model Expected shape of spectrum : –Differential index  ~ 2.1 for diffusive shock acceleration  observed ~ 2.7  source ~2.1;  ~ 0.6   esc (E) ~ E -0.6 c  esc  T disk ~100 TeV  Isotropy problem E max ~  shock Ze x B x R shock –  E max ~ Z x 100 TeV with exponential cutoff of each component –But spectrum continues to higher energy:  E max problem Expect p + gas   (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  0  -rays

12. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Knee Ankle Highest energy cosmic rays E max ~  shock Ze x B x R shock for SNR –  E max ~ Z x 100 TeV Knee: –Differential spectral index changes at ~ 3 x 10 15 eV –    –Some SNR can accelerate protons to ~10 15 eV (Berezhko) –How to explain 10 17 to >10 18 eV ? Ankle at ~ 3 x 10 18 eV: –Flatter spectrum –Suggestion of change in composition –New population of particles, possibly extragalactic? Look for composition signatures of “knee” and “ankle” Extragalactic? galactic

13. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser B. Peters on the knee and ankle B. Peters, Nuovo Cimento 22 (1961) 800 increases with E in knee region increases with E in knee region should begin to decrease again should begin to decrease again for E > 30 x E knee for E > 30 x E knee

14. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser 30 Rigidity-dependence Acceleration, propagation – depend on B: r gyro = R/B –Rigidity, R = E/Ze –E c (Z) ~ Z R c r SNR ~ parsec –  E max ~ Z * 10 15 eV – 1 < Z < 30 (p to Fe) Slope change should occur within factor of 30 in energy Characteristic pattern of increasing A with energy

15. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Models of galactic particles, E >> knee Axford: –continuity of spectrum over factor 300 of energy implies relation between acceleration mechanisms – reacceleration by multiple SNR Völk: – reacceleration by shocks in galactic wind (analogous to CIRs in heliosphere) Erlykin & Wolfendale: –Local source at knee on top of smooth galactic spectrum – (bending of “background” could reflect change in diffusion @ ~1 pc) What happens for E > 10 17 eV? Völk & Zirakashvili, 28 th ICRC p. 2031 Erlykin & Wolfendale, J Phys G27 (2001) 1005

16. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Lessons from the heliosphere ACE energetic particle fluences: Smooth spectrum –composed of several distinct components: Most shock accelerated Many events with different shapes contribute at low energy (< 1 MeV) Few events produce ~10 MeV –Knee ~ Emax of a few events –Ankle at transition from heliospheric to galactic cosmic rays R.A. Mewaldt et al., A.I.P. Conf. Proc. 598 (2001) 165

17. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Heliospheric cosmic rays ACE--Integrated fluences: –Many events contribute to low- energy heliospheric cosmic rays; –fewer as energy increases. –Highest energy (75 MeV/nuc) is dominated by low-energy galactic cosmic rays, and this component is again smooth Beginning of a pattern? R.A. Mewaldt et al., A.I.P. Conf. Proc. 598 (2001) 165

18. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Speculation on the knee K-H Kampert et al., astro-ph/0204205 Total protons helium CNO Mg… Fe 1 component:  = 2.7, E max = Z x 30 TeV; or Emax = Z x 1 PeV 3 components  

19. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Direct measurements to high energy with calorimeters RUNJOB: thanks to T. Shibata ATIC: thanks to E-S Seo & J. Wefel

20. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Recent Kascade data show increasing fraction of heavy nuclei Note anomalous He / proton ratio in recent Kascade analyses K-H Kampert et al., astro-ph/0204205 ICRC 2001 (Hamburg) M. Roth et al., Proc ICRC 2003 (Tsukuba) vol 1, p 139

21. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Chem. Composition 1 km 2 km Paper in proof at Astropart. Phys. AMANDA (number of muons ) Spase (number of electrons) Iron Proton log(E/PeV)

22. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Rates of contained, coincident events Area--solid-angle ~ 1/3 km 2 sr (including angular dependence of EAS trigger)

23. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Primary composition with IceCube N  from deep IceCube; N e from IceTop High altitude allows good energy resolution Good mass separation from N  /N e 1/3 km 2 sr (2000 x SPASE-AMANDA) Covers sub-PeV to EeV energies

24. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Power needed for knee component Integrate to E > 10 18 eV assuming –  esc ~ 2 x 10 7 yrs x E -1/3 – V galaxy ~  (15 kpc) 2 x 200 pc ~ 3 x 10 66 cm 3 –Total power for “knee” component ~ 2 x 10 39 erg/s Possible sources – Sources may be nearby – e.g.  -quasar SS433 at 3 kpc has L jet 10 39 erg/s –Eddington limited accretion ~ 2 x 10 38 erg/s

25. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Energy content of extra-galactic component depends on location of transition Composition signature: transition back to protons Uncertainties: Normalization point: 10 18 to 10 19.5 used Factor 10 / decade Spectral slope  =2.3 for rel. shock =2.0 non-rel. E min ~ m p (  shock ) 2

26. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Power needed for extragalactic cosmic rays assuming transition at 10 19 eV Energy density in UHECR,  CR ~ 2 x 10  erg/cm 3 –Such an estimate requires extrapolation of UHECR to low energy –  CR = (4  /c)  E  (E) dE = (4  /c){E 2  (E)}  E=10 19 eV x ln{E max /E min } –This gives  CR ~ 2 x 10  erg/cm 3 for differential index  = 2,  (E) ~ E -2 Power required ~  CR /10 10 yr ~ 1.3 x 10 37 erg/Mpc 3 /s –Estimates depend on cosmology and extragalactic magnetic fields: –3 x 10 -3 galaxies/Mpc 3 5 x 10 39 erg/s/Galaxy –3 x 10 -6 clusters/Mpc 3 4 x 10 42 erg/s/Galaxy Cluster –10 -7 AGN/Mpc 3 10 44 erg/s/AGN –~1000 GRB/yr 3 x 10 52 erg/GRB Assume E -2 spectrum. Then signal ~ 10 to 100/km 2 yr –~20% have E  >50 TeV (greater than atmospheric background)

27. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser GRB model Assume E -2 spectrum at source, normalize @ 10 19.5 10 45 erg/Mpc 3 /yr ~ 10 53 erg/GRB Evolution like star- formation rate GZK losses included Galactic  extragalactic transition ~ 10 19 eV Bahcall & Waxman, hep-ph/0206217 Waxman, astro-ph/0210638

28. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Berezinsky et al. AGN Assuming a cosmological distribution of sources with: –dN/dE ~ E -2, E < 10 18 eV –dN/dE ~ E , 10 18 < E < 10 21 –  = 2.7 (no evolution) –  = 2.5 (with evolution) Need L 0 ~ 3 ×10 46 erg/Mpc 3 yr They interpret dip at 10 19 as –p +  2.7   p + e + + e - Berezinsky, Gazizov, Grigorieva astro-ph/0210095

29. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Composition with air showers Cascade of nucleus –mass A, total energy E 0 –X = depth in atmosphere along shower axis –N(X) ~ A exp(X/ ), number of subshowers – E N ~ E 0 / N(X), energy/subshower at X –Shower maximum when E N = E critical –N(X max ) ~ E 0 / E critical –X max ~ ln { (E 0 /A) / E critical } –Most particles are electrons/positrons  from  -decay a distinct component – decay vs interaction depends on depth –N  ~ (A/E  ) * (E 0 /AE  ) 0.78 ~ A 0.22 Showers past max at ground (except UHE) –  large fluctuations –  poor resolution for E, A –Situation improves at high energy and/or high altitude –Fluorescence detection > 10 17 eV Schematic view of air shower detection: ground array and Fly’s Eye

30. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Change of composition at the ankle? Original Fly’s Eye (1993): transition coincides with ankle G. Archbold, P. Sokolsky, et al., Proc. 28 th ICRC, Tsukuba, 2003 HiRes new composition result: transition occurs before ankle

31. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Composition from density of muons ρ µ ( 600) vs. E 0 (Akeno, AGASA) From heavy toward protons

32. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Hi-Res stereo fluorescence detector in Utah UHE shower detectors AGASA (Akeno, Japan) 100 km 2 ground array Sketch of ground array with fluorescence detector – Auger Project realizes this concept

33. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Measuring the energy of UHECR Ground array samples shower front –Well-defined acceptance –Simulation relates observed ground parameter to energy Fluorescence technique tracks shower profile –Track-length integral gives calorimetric measure of energy –X max sensitive to primary mass: X max ~  ln(E 0 /A) protons penetrate more than heavier nuclei

34. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Complementarity Ground array –Assigning energies Measure a ground parameter (e.g.  (600) ) Compare to simulation Depends on model of hadronic interactions –Determining spectrum aperture set by physical boundary of array correct for attenuation of oblique showers Fluorescence detector –Assigning energies Infer S(X) from signals (depends on atmosphere) Fit shower profile, S(X) Integrate track-length: 2.19 eV/g/cm 2 ∫ S(X) dX Model-independent –Determining spectrum energy-dependent aperture must be simulated

35. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser AGASA 2 x 10 20 eV event

36. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Biggest event Comparison to –Proton showers –Iron showers –  showers Horizontal EAS –only muons survive –Haverah Park:  /p 10 19 eV –AGASA: similar limit Limit on  showers constrains TD models Fly’s Eye, Ap. J. 441 (1995) 295

37. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser The “Hillas Plot” (1984) E max ~  shock (ZeB) R Plot shows B, R to reach 10 20 eV Two more candidates since 1984 GRB jets Magnetars Active Galaxies, Gamma-ray Bursts favored

38. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Highest energy cosmic rays GZK cutoff? –Expected from p +  2.7   N +  for cosmological sources Attenuation length in microwave background Plot from HiRes, astro-ph/0208301

39. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Compare exposures: HiRes, AGASA 1700 km 2 sr yr AGASA HiRes: ~ 10 4 km 2 sr HiRes: ~ 10 4 km 2 sr x 0.05 efficiency x 0.05 efficiency x few years x few years ~2000 km 2 sr yr @ 10 20 eV ~2000 km 2 sr yr @ 10 20 eV AGASA: 180 km 2 srAGASA: 180 km 2 sr x 0.90 efficiency x 0.90 efficiency x 10 years x 10 years ~1700 km 2 sr yr ~1700 km 2 sr yr

40. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Akeno-AGASA / HiRes: comparison of what is measured As measured

41. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Models of UHECR Bottom up (acceleration) –Jets of AGN External Internal (PIC models) –GRB fireballs –Accretion shocks in galaxy clusters –Galaxy mergers –Young SNR –Magnetars Observed showers either protons (or nuclei) Top-down (exotic) –Radiation from topological defects –Decays of massive relic particles in Galactic halo –Resonant neutrino interactions on relic ’s (Z-burst) Large fraction of  showers (especially if local origin) ( Incomplete list ) If no cutoff, require a significant contribution from nearby sources. Local overdensity of galaxies is insufficient if UHECR source distribution follows distribution of galaxies. Violation of Lorentz invariance a way out?

42. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Active Galaxies: Jets VLA image of Cygnus A Radio Galaxy 3C296 (AUI, NRAO). --Jets extend beyond host galaxy. Drawing of AGN core

43. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser AGN Mulitwavelength observations SSC, EC, PIC models –1 st peak from electron synchrotron radiation –2 nd peak model-dependent; predict  flux if PIC –Interpretation complex: Sources variable Locations of peaks depend on source-- factor of >100 range of peak energy New detectors (GLAST, HESS, MAGIC, VERITAS) will greatly expand number, variety of sources Example of Mrk421 with new (preliminary) result from STACEE ~100 GeV Radio mm IR UV X-ray GeV  (Egret) TeV

44. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Questions Is B/C ~ E -0.3 at high energy? Are all antiprotons & positrons secondary? SN accelerate CR? Knee? Where is transition from galactic to extragalactic? E max (E min ) of cosmic accelerators? Wefel(3), Müller(5), Ptuskin (6) Müller (11) Ptuskin (4) Hörandel (7) Teshima (7) Ostrowski (3, 11)

45. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser More questions Do AGN or GRB accelerate (U)HERCR? Are AGN or GRB (or something else) sources? What are sources of super- GZK particles? Are there super-GZK particles? Stanev (11) Migneco(6), Sulak(10), Stanev(3) Teshima(9), Kuzmin(9) Klages (12)

46. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Cosmic-ray antiprotons secondary primary Secondary antiproton spectrum expected at Earth from cosmic-ray interactions in the ISM during propagation as compared to a “primary” source of antiprotons (TKG & E.H. Levy, 1974) Kinematic peak at 2 GeV characteristic of characteristic of p p  p p p p - p p  p p p p -

47. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Shock acceleration First order (diffusive) shock acceleration –“Fermi acceleration”--originally 2nd order –Power-law spectrum: dN/dE ~ E   = 2 for strong shock (large Mach number) –  E =  E at each shock crossing: dE/dt =  E / T cycle with T cycle ~ r L / c  shock ~ ( E / Ze B) / c  shock dE/dt =  (Ze B) c  shock E max ~  (Ze B) (c  shock T), after a time T  shock

48. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Uncertainty from spectral index The most promising accelerators involve relativistic shocks: –AGN:  ~ 30 GRB:  ~300 (  = bulk Lorentz factor) –Achterberg: Relativistic shocks have spectral index  ~ 2.2 - 2.3 –steeper spectral index  more power required –Recalculate energy density in UHECR: –  CR = (4  /c)  E  (E) dE ~  (10 19 ) x f(  ) x {1/E min }  -2 –  CR ~ 100 times  = 2 case for  ~ 2.3 and E min = m p ~ 1 GeV Problem for these models??? –Vietri: E min ~  2 for relativistic shocks –Reduces extra power factor to ~10 for AGN, ~ 3 for GRB –10 -7 AGN/Mpc 3 10 44 erg/s/AGN  10 45 erg/s/AGN –~1000 GRB/yr 3 x 10 52 erg/GRB  10 53 erg/GRB Neutrino signal enhanced somewhat, but steeper spectrum

49. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Large fluctuations in the knee region are worse at sea level Linear plot: green = e+/e-; blue =  Log plot: fluctuations bad at sea level 10 proton showers at 1 PeV

50. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Example: Fluctuations in N , N e at two depths

51. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Compare HiRes (mono) & AGASA Exposure (> 10 3 km 2 yr sr ): –comparable @ 10 20 eV –HiRes < AGASA at lower energy Number events >10 20 –HiRes (mono): 2 –AGASA: 11 Shift E down 20% so spectra agree then 5 AGASA events > 10 20 –Need more statistics and stereo results Fluorescence detectorGround array (astro-ph/0209422)

52. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser Depth of Maximum Combined HiRes/MIA hybrid plus new HiRes result suggest normalization of extra- galactic component at relatively low energy of 10 18 eV.

53. School of Cosmic-ray Astrophysics, Erice, July 3, 2004 Thomas K. Gaisser E/TeV Blazar spectra at high energy Mrk 421 & Mrk 501, –Cutoffs Intrinsic? Effect of propagation? –Variable sources Low intensity – softer spectrum Interpretation under debate –Need more observations of more sources at various redshifts HEGRA plots from Aharonian et al. astro-ph/0205499. Different E cut of 421 and 501 suggest cutoffs are intrinsic. Comparable analysis of Whipple extends to lower energy. Seeing comparable cutoffs, they suggest effect is due to propagation. Krennrich et al., Ap.J. 560 (2002) L45 both at z ~.03 igh ow