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Outstanding problems in Particle Astrophysics

Outstanding problems in Particle Astrophysics. Cosmic-ray propagation Acceleration Sources. Spectrometers ( D A = 1 resolution, good E resolution). Air showers. Calorimeters (less good resolution). Direct measurements. Knee. Ankle. A fundamental result.

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Outstanding problems in Particle Astrophysics

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  1. Outstanding problems in Particle Astrophysics Cosmic-ray propagation Acceleration Sources Thomas K. Gaisser

  2. Spectrometers (DA = 1 resolution, good E resolution) Air showers Calorimeters (less good resolution) Direct measurements Knee Ankle Thomas K. Gaisser

  3. A fundamental result • Excess of Li, Be, B from fragmentation of C, O • Spallation s plus rISM give dwell time of nuclei • Find t ~ 3 x 106 yrs • ct ~ Mpc >> size of galactic disk (kpc) • Suggests diffusion in turbulent ISM plasma • Predictions for g-rays, positrons and antiprotons follow Thomas K. Gaisser

  4. BESS antiprotons, 1997, ’99, ’00. • Fully consistent with secondary • production by collisions in ISM • followed by solar modulation • varying with solar cycle Diffuse galactic secondaries Phys.Rev.Lett. 88 (2002) 051101 p + gas  p0,p+/-, antiprotons • p0  g g [p+/-  n, m  e+/-] • Hard g-spectrum suggests some contribution from collisions at sources Thomas K. Gaisser

  5. Electrons & positrons • Primary electrons: • spectrum steeper than p • energy loss at high E • e+ as secondaries: • 5-10% fraction • level consistent with p + gas  p+  m+  e+ • Bump in charge ratio: • primary e+ ? … or • glitch in e- spectrum? Thomas K. Gaisser

  6. Energy-dependence of secondary/primary cosmic-ray nuclei • B/C ~ E-0.6 • Observed spectrum: • f(E) = dN/dE ~ K E-2.7 • Interpretation: • Propagation depends on E • t(E) ~ E-0.6 • f(E) ~ Q(E) x t(E) x (c/4p) • Implication: • Source spectrum Q(E) ~ E-2.1 Thomas K. Gaisser

  7. Spectral Energy Distribution (linear plot shows most E < 100 GeV) (4p/c) Ef(E) = local differential CR energy density Energetics of cosmic rays • Total local energy density: • (4p/c) ∫ Ef(E) dE ~ 10-12 erg/cm3 ~ B2 / 8p • Power needed: (4p/c) ∫ Ef(E) /tesc(E) dE galactic tesc ~ 107 E-0.6 yrs Power ~ 10-26 erg/cm3s • Supernova power: 1051 erg per SN ~3 SN per century in disk ~ 10-25 erg/cm3s • SN model of galactic CR Power spectrum from shock acceleration, propagation Thomas K. Gaisser

  8. Solar flare shock acceleration Coronal mass ejection 09 Mar 2000 Thomas K. Gaisser

  9. SOHO/ LASCO CME of 06-Nov 1997 Thomas K. Gaisser

  10. Particle with E1 u1 ~ 4/3 V Forward shock Contact discontinuity, V Shocked ISM SN ejecta u1 ~ 4/3 V E2 = x E1 Supernova blast wave acceleration Unshocked ISM Supernova progenitor SNR expands into ISM with velocity V~ 104 km/s. Drives forward shock at 4/3 V TSN ~ 1000 yrs before slowdown Emax ~ Z x 100 TeV Thomas K. Gaisser

  11. 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 Thomas K. Gaisser

  12. Knee galactic Ankle Highest energy cosmic rays • Emax ~ bshock Ze x B x Rshock for SNR •  Emax ~ Z x 100 TeV • Knee: • Differential spectral index changes at ~ 3 x 1015eV • a = 2.7  a = 3.0 • Some SNR can accelerate protons to ~1015 eV (Berezhko) • How to explain 1017 to >1018 eV ? • Ankle at ~ 3 x 1018 eV: • Flatter spectrum • Suggestion of change in composition • New population of particles, possibly extragalactic? • Look for composition signatures of “knee” and “ankle” Extragalactic? Thomas K. Gaisser

  13. B. Peters, Nuovo Cimento 22 (1961) 800 B. Peters on the knee and ankle <A> should begin to decrease again for E > 30 x Eknee < A > increases with E in knee region Thomas K. Gaisser

  14. 30 Rigidity-dependence • Acceleration, propagation • depend on B: rgyro = R/B • Rigidity, R = E/Ze • Ec(Z) ~ Z Rc • rSNR ~ parsec •  Emax ~ Z * 1015 eV • 1 < Z < 30 (p to Fe) • Slope change should occur within factor of 30 in energy • Characteristic pattern of increasing A with energy Thomas K. Gaisser

  15. Völk & Zirakashvili, 28th ICRC p. 2031 Erlykin & Wolfendale, J Phys G27 (2001) 1005 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 > 1017 eV? Thomas K. Gaisser

  16. 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. Mewaldtet al., A.I.P. Conf. Proc. 598 (2001) 165 Thomas K. Gaisser

  17. 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. Mewaldtet al., A.I.P. Conf. Proc. 598 (2001) 165 Thomas K. Gaisser

  18. 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 K-H Kampert et al., astro-ph/0204205 Speculation on the knee Thomas K. Gaisser

  19. Direct measurements to high energywith calorimeters RUNJOB: thanks to T. Shibata ATIC: thanks to E-S Seo & J. Wefel Thomas K. Gaisser

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

  21. Chem. Composition Iron 1 km Proton AMANDA (number of muons) log(E/PeV) 2 km Spase (number of electrons) Chemical Composition Paper in proof at Astropart. Phys. Thomas K. Gaisser

  22. Rates of contained, coincident events Area--solid-angle ~ 1/3 km2sr (including angular dependence of EAS trigger) Thomas K. Gaisser

  23. Primary composition with IceCube • Nm from deep IceCube; Ne from IceTop • High altitude allows good energy resolution • Good mass separation from Nm/Ne • 1/3 km2 sr (2000 x SPASE-AMANDA) • Covers sub-PeV to EeV energies Thomas K. Gaisser

  24. Power needed for knee component • Integrate to E > 1018 eV assuming • tesc ~ 2 x 107 yrs x E-1/3 • Vgalaxy ~ p (15 kpc)2 x 200 pc ~ 3 x 1066 cm3 • Total power for “knee” component ~ 2 x 1039 erg/s • Possible sources • Sources may be nearby • e.g. m-quasar SS433 at 3 kpc has Ljet 1039 erg/s • Eddington limited accretion ~ 2 x 1038 erg/s Thomas K. Gaisser

  25. Energy content of extra-galactic component depends on location of transition • Composition signature: • transition back to protons • Uncertainties: • Normalization point: • 1018 to 1019.5 used • Factor 10 / decade • Spectral slope • a=2.3 for rel. shock • =2.0 non-rel. • Emin ~ mp (gshock)2 Thomas K. Gaisser

  26. Power needed for extragalactic cosmic rays assuming transition at 1019 eV • Energy density in UHECR, CR ~ 2 x 10-19 erg/cm3 • Such an estimate requires extrapolation of UHECR to low energy • CR = (4/c)  E(E) dE = (4/c){E2(E)}E=1019eV x ln{Emax/Emin} • This gives CR ~ 2 x 10-19 erg/cm3 for differential index  = 2, (E) ~ E-2 • Power required ~ CR/1010 yr ~ 1.3 x 1037 erg/Mpc3/s • Estimates depend on cosmology and extragalactic magnetic fields: • 3 x 10-3 galaxies/Mpc3 5 x 1039 erg/s/Galaxy • 3 x 10-6 clusters/Mpc3 4 x 1042 erg/s/Galaxy Cluster • 10-7 AGN/Mpc3 1044 erg/s/AGN • ~1000 GRB/yr 3 x 1052 erg/GRB • Assume E-2 spectrum. Then n signal ~ 10 to 100/km2yr • ~20% have E>50 TeV (greater than atmospheric background) Thomas K. Gaisser

  27. GRB model Bahcall & Waxman, hep-ph/0206217 Waxman, astro-ph/0210638 • Assume E-2 spectrum at source, normalize @ 1019.5 • 1045 erg/Mpc3/yr • ~ 1053 erg/GRB • Evolution like star-formation rate • GZK losses included • Galactic extragalactic transition ~ 1019 eV Thomas K. Gaisser

  28. Berezinsky et al. AGN • Assuming a cosmological distribution of sources with: • dN/dE ~ E-2, E < 1018 eV • dN/dE ~ E-g, 1018< E < 1021 • g = 2.7 (no evolution) • g = 2.5 (with evolution) • Need L0 ~ 3 ×1046 erg/Mpc3 yr • They interpret dip at 1019 as • p + g2.7 p + e+ + e- Berezinsky, Gazizov, Grigorieva astro-ph/0210095 Thomas K. Gaisser

  29. Composition with air showers • Cascade of nucleus • mass A, total energy E0 • X = depth in atmosphere along shower axis • N(X) ~ A exp(X/l), number of subshowers • EN ~ E0 / N(X), energy/subshower at X • Shower maximum when EN = Ecritical • N(Xmax) ~ E0 / Ecritical • Xmax ~ l ln { (E0/A) / Ecritical } • Most particles are electrons/positrons • m from p-decay a distinct component • decay vs interaction depends on depth • Nm ~ (A/Em)*(E0/AEm)0.78 ~ A0.22 • 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 > 1017 eV Schematic view of air shower detection: ground array and Fly’s Eye Thomas K. Gaisser

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

  31. From heavy toward protons Composition from density of muonsρµ(600) vs. E0 (Akeno, AGASA) Thomas K. Gaisser

  32. Sketch of ground array with fluorescence detector – Auger Project realizes this concept Hi-Res stereo fluorescence detector in Utah AGASA (Akeno, Japan) 100 km2 ground array UHE shower detectors Thomas K. Gaisser

  33. 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 • Xmax sensitive to primary mass: Xmax ~ Lln(E0/A) protons penetrate more than heavier nuclei Thomas K. Gaisser

  34. 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/cm2 ∫ S(X) dX Model-independent Determining spectrum energy-dependent aperture must be simulated Complementarity Thomas K. Gaisser

  35. AGASA 2 x 1020 eV event Thomas K. Gaisser

  36. Biggest event Fly’s Eye, Ap. J. 441 (1995) 295 • Comparison to • Proton showers • Iron showers • g showers • Horizontal EAS • only muons survive • Haverah Park: g/p<40%, E>1019eV • AGASA: similar limit • Limit on g showers constrains TD models Thomas K. Gaisser

  37. GRB jets The “Hillas Plot” (1984) • Emax ~ bshock (ZeB) R • Plot shows B, R to reach 1020 eV • Two more candidates since 1984 Magnetars • Active Galaxies, • Gamma-ray Bursts favored Thomas K. Gaisser

  38. Plot from HiRes, astro-ph/0208301 Highest energy cosmic rays • GZK cutoff? • Expected from p + g2.7 N + p for cosmological sources Attenuation length in microwave background Thomas K. Gaisser

  39. 1700 km2 sr yr AGASA Compare exposures: HiRes, AGASA • HiRes: ~ 104 km2sr • x 0.05 efficiency • x few years • ~2000 km2 sr yr @ 1020 eV • AGASA: 180 km2sr • x 0.90 efficiency • x 10 years • ~1700 km2 sr yr Thomas K. Gaisser

  40. Akeno-AGASA / HiRes: comparison of what is measured As measured Thomas K. Gaisser

  41. 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 n’s (Z-burst) Large fraction of g-showers (especially if local origin) Models of UHECR ( 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? Thomas K. Gaisser

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

  43. Example of Mrk421 with new (preliminary) result from STACEE ~100 GeV UV IR TeV X-ray GeV g (Egret) mm Radio AGN Mulitwavelength observations • SSC, EC, PIC models • 1st peak from electron synchrotron radiation • 2nd peak model-dependent; predict n 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 Thomas K. Gaisser

  44. 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? Emax (Emin) of cosmic accelerators? Wefel(3), Müller(5), Ptuskin (6) Müller (11) Ptuskin (4) Hörandel (7) Teshima (7) Ostrowski (3, 11) Questions Thomas K. Gaisser

  45. Do AGN or GRB accelerate (U)HERCR? Are AGN or GRB (or something else) n 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) More questions Thomas K. Gaisser

  46. primary secondary Kinematic peak at 2 GeV characteristic of p p  p p p p- Cosmic-ray antiprotons 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) Thomas K. Gaisser

  47. Shock acceleration • First order (diffusive) shock acceleration • “Fermi acceleration”--originally 2nd order • Power-law spectrum: dN/dE ~ E-a • a = 2 for strong shock (large Mach number) • DE = xE at each shock crossing: • dE/dt = xE / Tcycle • with Tcycle ~ rL/ c bshock ~ ( E / Ze B) / c bshock • dE/dt = x (Ze B) c bshock • Emax ~ x (Ze B) (c bshockT), after a time T • x ~ bshock Thomas K. Gaisser

  48. 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 ~ (1019) x f() x {1/Emin}-2 • CR ~ 100 times  = 2 case for  ~ 2.3 and Emin = mp ~ 1 GeV • Problem for these models??? • Vietri: Emin ~ 2 for relativistic shocks • Reduces extra power factor to ~10 for AGN, ~ 3 for GRB • 10-7 AGN/Mpc3 1044 erg/s/AGN  1045erg/s/AGN • ~1000 GRB/yr 3 x 1052 erg/GRB  1053erg/GRB • Neutrino signal enhanced somewhat, but steeper spectrum Thomas K. Gaisser

  49. Large fluctuations in the knee region are worse at sea level Linear plot: green = e+/e-; blue = m Log plot: fluctuations bad at sea level 10 proton showers at 1 PeV Thomas K. Gaisser

  50. Example: Fluctuations in Nm, Neat two depths Thomas K. Gaisser

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