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School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Outstanding problems in Particle Astrophysics
Cosmic-ray propagation
Acceleration
Sources
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
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 106 yrs– c ~ Mpc >> size of
galactic disk (kpc)– Suggests diffusion in
turbulent ISM plasma– Predictions for -rays,
positrons and antiprotons follow
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
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?
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
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/cm3 ~ B2 / 8
• Power needed:(4/c) ∫ E(E) / esc(E) dEgalacticesc ~ 107 E-0.6 yrsPower ~ 10-26 erg/cm3s
• Supernova power:1051 erg per SN~3 SN per century in disk~ 10-25 erg/cm3s
• SN model of galactic CRPower spectrum from shock
acceleration, propagation
Spectral Energy Distribution (linear plot shows most E < 100 GeV) (4/c) E(E) = local differential CR energy density
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Solar flare shock acceleration
Coronal mass ejectionCoronal mass ejection 09 Mar 200009 Mar 2000
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
SOHO/LASCO
CME of 06-Nov 1997
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~ 104 km/s.Drives forward shock at 4/3 V
Forward shock
u1 ~ 4/3 V
u1 ~ 4/3 V
Particle with E1
E2 = E1
Contact discontinuity, V
TSN ~ 1000 yrs before slowdownEmax ~ Z x 100 TeV
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 ~ 2.7source ~2.1; ~
0.6 esc(E) ~ E-0.6
• c esc Tdisk ~100 TeV
Isotropy problem
• Emax ~ shock 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 (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
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Knee
AnkleAnkle
Highest energy cosmic rays• Emax ~ shock Ze x B x Rshock for SNR
Emax ~ Z x 100 TeV• Knee:
– Differential spectral index changes at ~ 3 x 1015eV
– – 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?Extragalactic?
galacticgalactic
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
< A > increases with E in knee region< A > increases with E in knee region<A> should begin to decrease again<A> should begin to decrease again for E > 30 x Efor E > 30 x Ekneeknee
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
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
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 > 1017 eV?
Völk & Zirakashvili, 28th ICRC p. 2031
Erlykin & Wolfendale, J Phys G27 (2001) 1005
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
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
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
CNOMg…
Fe
1 component: = 2.7, Emax = Z x 30 TeV; or Emax = Z x 1 PeV
3 components
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Direct measurements to high energywith calorimeters
RUNJOB: thanks to T. ShibataATIC: thanks to E-S Seo & J. Wefel
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
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Chem. Composition
1 km
2 km
Paper in proof at Astropart. Phys.
AM
AN
DA
(nu
mbe
r o
f m
uons
)
Spase (number of electrons)
Iron
Proton
log(E/PeV)
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Rates of contained, coincident eventsArea--solid-angle ~ 1/3 km2sr (including angular dependence of EAS trigger)
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Primary composition with IceCube
• N from deep IceCube; Ne from IceTop
• High altitude allows good energy resolution
• Good mass separation from N/Ne
• 1/3 km2 sr (2000 x SPASE-AMANDA)
• Covers sub-PeV to EeV energies
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Power needed for knee component
• Integrate to E > 1018 eV assuming – esc ~ 2 x 107 yrs x E-1/3
– Vgalaxy ~ (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. -quasar SS433 at 3 kpc has Ljet 1039 erg/s
– Eddington limited accretion ~ 2 x 1038 erg/s
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:
1018 to 1019.5 usedFactor 10 / decade
• Spectral slope =2.3 for rel. shock =2.0 non-rel.
• Emin ~ mp (shock)2
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Power needed for extragalactic cosmic rays assuming transition at 1019 eV
• Energy density in UHECR, CR ~ 2 x 10 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 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 signal ~ 10 to 100/km2yr
– ~20% have E>50 TeV (greater than atmospheric background)
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
GRB model
• 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
Bahcall & Waxman, hep-ph/0206217Waxman, astro-ph/0210638
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 < 1018 eV
– dN/dE ~ E, 1018< E < 1021
– = 2.7 (no evolution)
– = 2.5 (with evolution)
• Need L0 ~ 3 ×1046 erg/Mpc3 yr
• They interpret dip at 1019 as– p + 2.7p + e+ + e-
Berezinsky, Gazizov, Grigorieva astro-ph/0210095
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Composition with air showers• Cascade of nucleus
– mass A, total energy E0 – X = depth in atmosphere along shower axis– N(X) ~ A exp(X/), number of subshowers– EN ~ E0 / N(X), energy/subshower at X– Shower maximum when EN = Ecritical
– N(Xmax) ~ E0 / Ecritical
– Xmax ~ ln { (E0/A) / Ecritical }– Most particles are electrons/positrons
• from -decay a distinct component– decay vs interaction depends on depth– N ~ (A/E)*(E0/AE)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
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. 28th ICRC, Tsukuba, 2003
HiRes new composition result: transition occurs before ankle
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Composition from density of muonsρµ(600) vs. E0 (Akeno, AGASA)
From heavy
toward protons
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 km2 ground array
Sketch of ground array with fluorescence detector – Auger Project realizes this concept
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– Xmax sensitive to primary mass:
Xmax ~ ln(E0/A)protons penetrate more than
heavier nuclei
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/cm2 ∫ S(X) dX
• Model-independent
– Determining spectrum• energy-dependent aperture
• must be simulated
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
AGASA 2 x 1020 eV event
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<40%, E>1019eV
– AGASA: similar limit
• Limit on showers constrains TD models
Fly’s Eye, Ap. J. 441 (1995) 295
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
The “Hillas Plot” (1984)
• Emax ~ shock (ZeB) R
• Plot shows B, R to reach 1020 eV
• Two more candidates since 1984
GRB jets
Magnetars
•Active Galaxies,Gamma-ray Bursts favored
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Highest energy cosmic rays• GZK cutoff?
– Expected from p + 2.7N + for cosmological sources
Attenuation length in microwave backgroundPlot from HiRes, astro-ph/0208301Plot from HiRes, astro-ph/0208301
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Compare exposures: HiRes, AGASA
1700 km1700 km22 sr yr sr yrAGASAAGASA
• HiRes: ~ 10HiRes: ~ 1044 km km22srsr x 0.05 efficiencyx 0.05 efficiency x few yearsx few years ~2000 km~2000 km22 sr yr @ 10 sr yr @ 102020 eV eV
•AGASA: 180 kmAGASA: 180 km22srsr x 0.90 efficiencyx 0.90 efficiency x 10 yearsx 10 years ~1700 km~1700 km22 sr yr sr yr
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Akeno-AGASA / HiRes: comparison of what is measured
As measured
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 contributionfrom nearby sources. Local overdensity ofgalaxies is insufficient if UHECR sourcedistribution follows distribution of galaxies.Violation of Lorentz invariance a way out?
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Active Galaxies: JetsActive Galaxies: Jets
VLA image of Cygnus A
Radio Galaxy 3C296 (AUI, NRAO). --Jets extend beyond host galaxy.
Drawing of AGN core
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
AGN Mulitwavelength observations
• SSC, EC, PIC models– 1st peak from electron
synchrotron radiation
– 2nd 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
Rad
io
mm
IRUV
X-rayGeV (Egret)
TeV
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?• Emax (Emin) of cosmic
accelerators?
• Wefel(3), Müller(5), Ptuskin (6)
• Müller (11)
• Ptuskin (4)• Hörandel (7)• Teshima (7)
• Ostrowski (3, 11)
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)
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Cosmic-ray antiprotons
secondarysecondary
primaryprimary
Secondary antiproton spectrum expected at Earth from Secondary antiproton spectrum expected at Earth from cosmic-ray interactions in the ISM during propagation as cosmic-ray interactions in the ISM during propagation as compared to a “primary” source of antiprotonscompared to a “primary” source of antiprotons(TKG & E.H. Levy, 1974)(TKG & E.H. Levy, 1974)
Kinematic peak at 2 GeVKinematic peak at 2 GeV characteristic ofcharacteristic of p p p p p p p p p p p p--
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 / Tcycle • with Tcycle ~ rL/ c shock ~ ( E / Ze B) / c shock • dE/dt = (Ze B) c shock • Emax ~ (Ze B) (c shock T), after a time T• shock
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 ~ (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 1045 erg/s/AGN – ~1000 GRB/yr 3 x 1052 erg/GRB 1053 erg/GRB
• Neutrino signal enhanced somewhat, but steeper spectrum
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
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Example: Fluctuations in N, Ne
at two depths
School of Cosmic-ray Astrophysics, Erice, July 3, 2004
Thomas K. Gaisser
Compare HiRes (mono) & AGASA
• Exposure (>103 km2 yr sr):– comparable @ 1020 eV– HiRes < AGASA at
lower energy
• Number events >1020
– HiRes (mono): 2– AGASA: 11
• Shift E down 20% so spectra agree then
• 5 AGASA events > 1020
– Need more statistics and stereo results
Fluorescence detector Ground array
(astro-ph/0209422)(astro-ph/0209422)
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 1018 eV.
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. DifferentEcut 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