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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

Outstanding problems in Particle Astrophysics

Cosmic-ray propagation

Acceleration

Sources

Thomas K. Gaisser


Spectrometers

(DA = 1 resolution,

good E resolution)

Air

showers

Calorimeters

(less good resolution)

Direct measurements

Knee

Ankle

Thomas K. Gaisser


A fundamental result
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


Diffuse galactic secondaries

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


Electrons positrons
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


Energy dependence of secondary primary cosmic ray nuclei
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


Energetics of cosmic rays

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


Solar flare shock acceleration
Solar flare shock acceleration

Coronal mass ejection

09 Mar 2000

Thomas K. Gaisser


SOHO/

LASCO

CME of

06-Nov

1997

Thomas K. Gaisser


Supernova blast wave acceleration

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


Problems of simplest snr shock model

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


Highest energy cosmic rays

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


B peters on the knee and ankle

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


Rigidity dependence

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


Models of galactic particles e knee

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


Lessons from the heliosphere
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


Heliospheric cosmic rays
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


Speculation on the knee

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


Direct measurements to high energy with calorimeters
Direct measurements to high energywith calorimeters

RUNJOB: thanks to T. Shibata

ATIC: thanks to E-S Seo & J. Wefel

Thomas K. Gaisser


Recent kascade data show increasing fraction of heavy nuclei

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


Chem composition
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


Rates of contained coincident events
Rates of contained, coincident events

Area--solid-angle ~ 1/3 km2sr

(including angular dependence of EAS trigger)

Thomas K. Gaisser


Primary composition with icecube
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


Power needed for knee component
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


Energy content of extra galactic component depends on location of transition
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


Power needed for extragalactic cosmic rays assuming transition at 10 19 ev
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


Grb model
GRB model transition at 10

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


Berezinsky et al agn
Berezinsky et al. AGN transition at 10

  • 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


Composition with air showers
Composition with air showers transition at 10

  • 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


Change of composition at the ankle

HiRes new composition result: transition at 10

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


Composition from density of muons 600 vs e 0 akeno agasa

From heavy transition at 10

toward protons

Composition from density of muonsρµ(600) vs. E0 (Akeno, AGASA)

Thomas K. Gaisser


Uhe shower detectors

Sketch of ground array with transition at 10

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


Measuring the energy of uhecr
Measuring the energy of UHECR transition at 10

  • 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


Complementarity

Ground array transition at 10

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


Agasa 2 x 10 20 ev event
AGASA 2 x 10 transition at 1020 eV event

Thomas K. Gaisser


Biggest event
Biggest event transition at 10

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


The hillas plot 1984

GRB jets transition at 10

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


Highest energy cosmic rays1

Plot from HiRes, astro-ph/0208301 transition at 10

Highest energy cosmic rays

  • GZK cutoff?

    • Expected from p + g2.7 N + p for cosmological sources

Attenuation length in microwave background

Thomas K. Gaisser


Compare exposures hires agasa

1700 km transition at 102 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


Akeno agasa hires comparison of what is measured
Akeno-AGASA / HiRes: transition at 10 comparison of what is measured

As measured

Thomas K. Gaisser


Models of uhecr

Bottom up (acceleration) transition at 10

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


Active galaxies jets
Active Galaxies: Jets transition at 10

Radio Galaxy 3C296 (AUI, NRAO).

--Jets extend beyond host galaxy.

Drawing of AGN core

VLA image of Cygnus A

Thomas K. Gaisser


Agn mulitwavelength observations

Example of Mrk421 with new (preliminary) transition at 10

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


Questions

Is B/C ~ E transition at 10-0.3 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


More questions

Do AGN or GRB accelerate (U)HERCR? transition at 10

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


Cosmic ray antiprotons

primary transition at 10

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


Shock acceleration
Shock acceleration transition at 10

  • 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


Uncertainty from spectral index
Uncertainty from spectral index transition at 10

  • 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


Large fluctuations in the knee region are worse at sea level
Large fluctuations in the knee region are worse at sea level transition at 10

Linear plot: green = e+/e-; blue = m

Log plot: fluctuations bad at sea level

10 proton showers at 1 PeV

Thomas K. Gaisser


Example fluctuations in n m n e at two depths
Example: Fluctuations in N transition at 10m, Neat two depths

Thomas K. Gaisser


Compare hires mono agasa

(astro-ph/0209422) transition at 10

Compare HiRes (mono) & AGASA

Fluorescence detector

Ground array

  • 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

Thomas K. Gaisser


Depth of maximum
Depth of Maximum transition at 10

Combined HiRes/MIA hybrid plus new HiRes result suggest normalization of extra-galactic component at relatively low energy of 1018 eV.

Thomas K. Gaisser


Blazar spectra at high energy

E/TeV transition at 10

igh

ow

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

both at z ~ .03

HEGRA plots from Aharonian et al.

astro-ph/0205499. Different

Ecut 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

Thomas K. Gaisser


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