the cosmic-ray spectrum
DESCRIPTION
The cosmic-ray spectrum. From the knee to the ankle. Spectrometers ( D A = 1 resolution, good E resolution). Air showers. Calorimeters (less good resolution). Air-shower arrays on the ground to overcome low flux. Don’t see primaries directly. Direct measurements. Knee. Ankle. - PowerPoint PPT PresentationTRANSCRIPT
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Aspen, April 26, 2005 Tom Gaisser
The cosmic-ray spectrum
From the knee to the ankle
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Aspen, April 26, 2005 Tom Gaisser
Spectrometers (A = 1 resolution, good E resolution)
Calorimeters (less good resolution)
Direct measurements
Air showers
Air-shower arrays on the ground to overcome low flux.Don’t see primaries directly.
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Aspen, April 26, 2005 Tom Gaisser
Theme of this talk
• SNR shock model of cosmic-ray origin based on– Energy content– Composition– Spectrum
• Full spectrum: three energy regions– < PeV (up to the knee)– PeV – EeV (knee – ankle)– > EeV (UHECR)
• Where is transition from galactic to extra-galactic cosmic rays? – Use spectrum, composition, energy content also to
answer questions at high energy
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Aspen, April 26, 2005 Tom 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
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Aspen, April 26, 2005 Tom 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
• With characteristic pattern of increasing A
• Problem: continuation of smooth spectrum to EeV
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Aspen, April 26, 2005 Tom Gaisser
B. Peters on the knee and ankle
B. Peters, Nuovo Cimento 22 (1961) 800
Peters cyclePeters cycle: systematic increase of < A > : systematic increase of < A > approaching Eapproaching Emaxmax
<A> should begin to decrease again<A> should begin to decrease again for E > 30 x Efor E > 30 x Ekneeknee
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Aspen, April 26, 2005 Tom Gaisser
Direct measurements to high energyshow no strong features below PeV
R. Battiston, Rapporteur talk, Tsukuba, 2003
RUNJOB: thanks to T. ShibataATIC: thanks to E-S Seo & J. Wefel
/nucleon)
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Aspen, April 26, 2005 Tom Gaisser
All-particle spectrum:Knee ~3 PeV
Tibet EE/1.23
x 0.1
x 0.01
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Aspen, April 26, 2005 Tom Gaisser
Recent Kascade data show increasing fraction of heavy nuclei with expected cutoff
sequence starting at ~3 PeV
K-H Kampert et al., astro-ph/0204205 ICRC 2001 (Hamburg)
M. Roth et al., Proc ICRC 2003 (Tsukuba) vol 1, p 139No information > 1017 eV
from original Kascade
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Aspen, April 26, 2005 Tom Gaisser
Models of galactic particles, E >> knee
• Fine-tuning problem:– continuity of spectrum over factor
300 of energy implies relation between acceleration mechanisms
• Axford:– reacceleration by multiple SNR
• Jokipii & Morfill, Völk:– reacceleration by shocks in
galactic wind (termination shock or CIRs)
• Erlykin & Wolfendale:– Local source at knee on top of
smooth galactic spectrum– (bending of “background” could
reflect change in diffusion • What happens for E > 1017 eV?
– Hillas: component B
Völk & Zirakashvili, 28th ICRC p. 2031
Erlykin & Wolfendale, J Phys G27 (2001) 1005
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Aspen, April 26, 2005 Tom Gaisser
Speculation on the knee
Total
protons
helium
CNOMg…
Fe
1 component: = 2.7, Emax = Z x 30 TeV; (Lagage & Cesarsky)
or Emax = Z x 1 PeV
3 components
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Aspen, April 26, 2005 Tom Gaisser
Power needed for knee B-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 “B” 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– Neutron source at GC ~ 1038 erg/s
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Aspen, April 26, 2005 Tom Gaisser
Where is transition to extragalactic CR?
G. Archbold, P. Sokolsky, et al.,Proc. 28th ICRC, Tsukuba, 2003
HiRes new composition result: transition occurs before ankle
Original Fly’s Eye (1993): transition coincides with ankle
3 EeV
0.3 EeV
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Aspen, April 26, 2005 Tom 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
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Aspen, April 26, 2005 Tom Gaisser
New detectors to explore galactic to extra-galactic transition
• Need > km2 to reach EeV
• KASCADE-Grande
• IceCube (including IceTop)
• Tunka – 133
• “Hybrid” Hi-Res, TA, Auger– below nominal threshold
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piering
Three new kilometer-scale detectors
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Aspen, April 26, 2005 Tom Gaisser
New South Pole station with IceTop Station 21 in foreground
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Aspen, April 26, 2005 Tom Gaisser
Two DOMs: 10” PMTOne high-gain; one low-gain in each tank
To DAQ
IceCubeDrill Hole
10 m
HG HG LGLG
Junction box
25 m
IceTop station
• Two Ice Tanks 2.7 m2 x 0.9 m deep (scaled-down version of Haverah, Auger)• Integrated with IceCube: same hardware, software• Coincidence between tanks = potential air shower• Local coincidence with no hit at neighboring station tags muon in deep detector• Signal in single tank = potential muon• Significant area for horizontal muons• Low Gain/High Gain operation to achieve dynamic range• Two DOMs/tank gives redundancy against failure of any single DOM
because only 1 low-gain detector is needed per station
~ 5-10 TeV
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Aspen, April 26, 2005 Tom Gaisser
DOMs in tank before freezing
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Aspen, April 26, 2005 Tom Gaisser
Dec 04: 4 stations, 8 tanks
Serap will present IceCube/IceTop on Saturday
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Aspen, April 26, 2005 Tom Gaisser
Importance of locating transition to extra-galactic component:
energy content depends on it
• 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
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Aspen, April 26, 2005 Tom Gaisser
Power needed for extragalactic cosmic rays (assuming transition at 1019 eV)
• Energy in extra-galactic, CR ~ 2 x 10 erg/cm3
– Includes 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 ; significantly more if > 2,
• Power required ~ CR/1010 yr ~ 1.3 x 1037 erg/Mpc3/s– Estimates depend on cosmology + 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
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Aspen, April 26, 2005 Tom Gaisser
Bahcall & Waxman (GRB)
• Galactic extragalactic transition ~ 1019 eV
• Assume E-2 spectrum at source, normalize @ 1019.5
• 1045 erg/Mpc3/yr• ~ 1053 erg/GRB• Evolution ~ star-formation• GZK losses included
Physics Letters B556 (2003) 1
Bahcall & Waxman hep-ph/0206217
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Aspen, April 26, 2005 Tom Gaisser
Berezinsky et al.: AGN
• G E-G transition < 1018 eV• Assume 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
• Interpret ankle at 1019 as– p + 2.7p + e+ + e-
Berezinsky, Gazizov, Grigorieva astro-ph/0210095
astro-ph/0410650
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Aspen, April 26, 2005 Tom Gaisser
Questions to ponder
• How to boost Emax to 100 PeV– perpendicular shocks? – self-generated higher magnetic fields?
• What is the energy-dependence of diffusion?• What is the source spectrum?
– Are there different slopes for different sources?– How to use the characteristic concave shape of non-linear
diffusive shock acceleration?
• How many sources? How are they distributed?
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Aspen, April 26, 2005 Tom 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
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Aspen, April 26, 2005 Tom Gaisser
Solar flare shock acceleration
Coronal mass ejectionCoronal mass ejection 09 Mar 200009 Mar 2000
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Aspen, April 26, 2005 Tom Gaisser
SOHO/LASCO
CME of 06-Nov 1997
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Aspen, April 26, 2005 Tom 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
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Aspen, April 26, 2005 Tom Gaisser
Questions to ponder
• How to boost Emax to 100 PeV– perpendicular shocks? – self-generated higher magnetic fields?
• What is the energy-dependence of diffusion?• What is the source spectrum?
– Are there different slopes for different sources?– How to use the characteristic concave shape of non-linear
diffusive shock acceleration?
• How many sources? How are they distributed?