Download Cosmic Rays

Cosmic Rays:
what we do (not) know 95
years after the discovery
Adrian Biland, ETH Zurich
Graz, 29.Nov.2007
Graz, 29.Nov.2007
A.Biland: Cosmic Rays
1
- History
- Direct CR Observations;
‘low’ Energy
- Indirect CR Observations;
‘high’ Energy
- Possible CR Sources
& Accelerators
Graz, 29.Nov.2007
A.Biland: Cosmic Rays
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CR History
1896 Bequerel discovers Radioactivity
(birth of Nuclear Physics)
1900 Wilson measures conductivity of air
(postulates extraterr. radiation that ionizes air)
1910
.
1911
.
Gockel shows that air in 4000m still
conductive
F.Zwicky postulates Supernovae as
source of radiation
(since few years, we know the ‘crazy swiss’
had been [partially] correct once more)
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CR History
1912 Hess measures
height-dependency
of conductivity =>
more ionization at
high altitudes ==>
can’t be terrestrial
radiation
‘Birth of CRPhysics’
1936 Nobel Prize
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CR History
1919
1926
.
1927
.
Kolhoerster: Energy > known radioact.Elem.
Int. Physics Symposium accepts existence of
‘ultraradiation of unknown origin’
Clay: less radiation at aequator than at pole
=> must be affected by magnetic field
=> must be charged particles (*)
1930 Rossi: Air-showers; soft and hard component
. (absorbed by 1cm Pb | penetrates 1m Pb)
1931 Dirac postulates e+ (from QED)
1932 Anderson identifies e+ in air showers
‘Birth of Particle Physics’
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(*)
Clay indicated in 1926
that CR must be charged
particles.
But (at least in USA)
dispute about charged
particles vs. gamma-rays
continued for many years
Millikan vs. Compton
==> The New York Times
headline in Dec. 1932:
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CR History
1935
1937
.
.
1938
.
Yukawa postulates ‘Meson’ (m ~300me)
Anderson & Neddermeyer find
‘Mesotron’ in showers (m ~50-1000me)
(- 1947) can’t be Yukawa particle
Auger detects ‘large showers’ >500m2
==> Energy >1000 TeV (LHC: 14TeV)
1947 +- found in showers =>Yukawa part.
. ==> Mesotron is new particle class: 
1949
0 found in showers
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~ 40 km
Primary cosmic
particle
~ 15 km
Atmosphere
Air shower
(secondary
particles)
±  ± 
o    -> e+e- ->  …

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
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Since ~1950:
- Accelerators ----> SM
- Understanding of shower
development (Monte Carlo)
- Satellites
==> more Information about
Primary cosmic Radiation:
-Mainly p and charged Ions
-Power law, but ‘knee’ ~1015eV
and ‘ankle’ ~1018eV
Energy range >12 decades
Flux range
>32 decades
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Since ~1950:
- Accelerators ---> SM
- Understanding of shower
development (Monte Carlo)
- Satellites
I(E) ~ E– 
==> more Information about
Primary cosmic Radiation:
-Mainly p and charged Ions
-Power law, but ‘knee’ ~1015eV
and ‘ankle’ ~1018eV
Energy range >12 decades
Flux range
>32 decades
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(  History )
1930: Pauli postulates 
1956: Cowan & Reines find  (Reactor)
Since 1965: Davis searches for solar 
flux factor ~3 too low (Astro)
1987: first (only) extrasolar (extragalagtic)
-source seen: SN-1987A (Astro)
1989: exist three generations <45GeVAcceler.
1998: -oszillation ==>
-mass from air-shower  !!! (CR !!!)
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- History
- Direct CR Observations;
‘low’ Energy
- Indirect CR Observations;
‘high’ Energy
- Possible CR Sources
& Accelerators
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Direct CR Observation
CR-particles with
E < ~10TeV can
(and should) be
observed above
atmosphere
Direct
observations
Solar modulation
Below 20 GeV:
‘solar modulation’
shielding by the
(variable) solar
wind and B-field
must be taken into account
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Effect of Solar Shielding
measured
proton flux
above (south)
pole
compared
to calculated
flux outside
Heliosphere
Depending on solar
activity, CR flux
<20GeV can vary
by more than 20%
==> difficult to compare measurements...
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CR Abundance
Chemical composition
of CR shows good
agreement with
‘metal’ ratios in
interplanetary
matter [IPM]
CR
~85% p
~12% He
~ 2% e~ 1% ‘metals’
( E < 3GeV)
even/odd structure:
Binding Energy
Large disagreement @
‘solar system’ (IPM)
Li, Be, B, F, ‘sub-Fe’
too much in CR or too few in IPM ?
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Abundance vs. Solar Activity
Solar minimum
integr. CR flux
Solar maximum
While total CR
flux varies with
solar activity,
rel. abundance
stays constant
==> difference
not from solar
modulation ...
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lifespan of a star with
25 solar masses: <107 y
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Production of Heavy Elements
Main fusion-processes in (heavy) stars:
 4He
 12C
 14N
 16O
 20Ne 4He
 23Na p
 24Mg
16O +16O  28Si 4He
 31P p
 32S
+ e-,e+,,..
…
4p
3 4He
12C +2p
12C +4He
12C +12C
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No (major) process
to produce Li,Be,B,F
Suppressed in
‘standard’ matter
Do CR-sources
produce nonstandard matter?
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Our Galaxy
1pc=3.26Ly
<Bgal> ~3G  p: 10GeV r ~ 10-5pc
1015eV r ~ rgal
(low-energy) CR trapped in Galaxy
‘Rigidity’: momentum / charge [GV]
 particles with same rigidity follow same trajectory in B-field
Interstellar Matter [ISM]: ISM ~ 1 1H/cm3
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Spallation
CR does not travel in vacuum:
e.g.
12C
CR
‘primary’
+ 1HISM 
10B
CR +
‘secondary’
X
(X: p, 0, ++me+em)
known cross-section (measured in lab):
need ~6 g/cm2 ISM to be traversed
to explain CR abundance (C/B ratio)
ISM~ 2 10-24g/cm3
==> CR travels ~3 1024cm ~1 Mpc
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Propagation Model
Goal:
One model should explain all ratios,
as well as antiproton- and positronrates and diffuse gamma-flux (0)
Unknown details about our galaxy
(exact ISM distribution, B-field, …)
and CR-sources do automatically
cancel if looking only at ratios !!!
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Leaky Box Model
Occurrence for each Isotope i at Energy E:
Acceleration
at Source(s)
Energy
dependent
leaking out
of magn. Bottle
Isotope loss by:
Collision | Radioact.
with ISM | decay
Isotope creation
by Spallation or
radioact. decay
from Isotope k
Higher Energy particles can escape B-field easier, i.e.
average ‘age’ of high-energy CR lower less secondaries
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‘extended’ Models
‘Nested Leaky-Box’:
Strong B-field close to sources 
CR must first leak-out source region
(probably  > ISM)
‘Reacceleration’:
CR that is accelerated at sources
does already contain secondaries
from ‘older’ sources
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‘extended’ Models
‘Diffusion Model’:
assume more physical escapemechanism than just ‘leakage’
 predict (small) density gradients
 expect (small) anisotropies
Others
(E-loss by Ionisation, Radiation, …)
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B/C Ratio
Reference fit,
to be applied
to other ratios
Problems:
-large experim.
errors
-disagreement
between exp.
==> can not
really test models
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Calculated Abundances
~1GeV/Z
no Li, Be, B at
source
>50% of C,O,Mg
Si,... destroyed
by spallation
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Direct Measurement of CR Age
Secondary Isotopes
with lifetime ~esc
can be used to
directly measure
the age of CR
e.g.CR could stay for long
time in regions with low ISM and high B ?
need more precise measurements ...
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Some Actual Results
excess ???
Positron Flux
need more precise
measurements ...
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Some Actual Results
e+ and anti-p could also be produced in
decays of (hypothetical) dark-matter
particles; should result in different
energy spectra than in CR predictions
==>
need much more precise measurements ...
[even if most CR physicists are more interested
on the highest energy questions ... ]
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Balloons (mainly in Antarctica)
e.g.: BESS
direct cosmic ray
(since 1992,
~3d/year
100d/y planned)
AMS@ISS (20XY)
put particle physics detectors
outside of the atmosphere
Satellites: PAMELA
(on russian Satellite;
launch 15.June 2006)
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AMS-02
p-flux
He-flux
Predicted performance …
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AMS-02
==> search for new Physics
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Differential Fluxes
Heavy elements (Fe)
should show harder
spectrum than light
elements (He, C)
because of shorter
interaction length
Are high-energy CR
dominated by Fe
instead of H ?
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- History
- Direct CR Observations;
‘low’ Energy
- Indirect CR Observations;
‘high’ Energy
- Possible CR Sources
& Accelerators
Graz, 29.Nov.2007
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Primary CR-Spectrum
Above few 10 TeV:
no longer possible
to directly measure
CR-particles:
Flux too low
==> need too large
detector
CR-spectrum looks boring/feature-less except:
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Primary CR-Spectrum
~ 20
events..?
galactic ? extragalactic ?
confined
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not confined by gal.B-field
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‘Air-Calorimeter’
Cannot use satellites or balloons
to measure CR > 100 TeV:
Use atmosphere as a ‘calorimeter’
Problems:
-
not constant density
not constant temperature
not constant composition (e.g. clouds)
…
(and everything varies with time)
how to read it out ???
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Atmosphere
Total atmosphere
~ 1000 g/cm2
side remark: at 40km,
still few g/cm2 left
For detailed calculations,
have to take into account
some local temperature
and pressure variations
(e.g: winter/summer !)
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CR + Atmosphere ?
produce mainly
0, +, -
do full MC
study, but:
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0 in Atmosphere ?
Decays immediately into 2, [ c=25.1nm ]
producing electromagnetic (sub)showers
pair-production
Bremsstrahlung
R~9/7 X0~45g/cm2
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(in air, 20oC)
40
+- in Atmosphere ?
decay:
+ --> +
lifetime: c ~ 8m
Mass: 0.13 GeV
==> 150 GeV +-: d=c=1150x8m ~9km
==> most would reach earth before decay
but nuclear interaction (same as p or n)
attenuation length in air: p,n ~120 g/cm2
+- ~160 g/cm2
==> production of new p,n, +-0
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+- in Atmosphere ?
Upper atmosphere ~isothermal
==> ‘depth’[g/cm2] ~ X e(-h/H) , H~6.5km
==> E+- >> 10 GeV:
interaction before decay
<~ 10 GeV: [ d < 600m ]
decay before interaction
==> atmospheric ,
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+- in Atmosphere ?
decay:
+ --> ee+
==> atmospheric e
lifetime: c ~ 600m
Mass: 0.105GeV
==> 2 GeV +-: d=c=19x600m ~11km
==> reach earth before decaying
energy-loss: (Ionization, …)
loose ~ 2GeV in atmosphere (1000g/cm2)
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500 GeV Showers:
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100 TeV Showers:
(>1GeV)
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(>1GeV)
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How to Readout ‘Calorimeter’
- Measure  (at sea-level or underground)
- Measure shower-tails (at high altitudes)
- Ionization --> Recombination
Fluorescence light
- Shower-particles relativistic ==>
emit Cherenkov light (300-700nm)
- (sound waves; radio waves; … ???)
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atmospheric 
Best detectors:
go to accelerator experim.
also disadvantages:
- not homogen. shielding
(large access-shafts)
- not homogen. inside
(‘unneeded’ calorimeters)
- …
L3@LEP
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needed >10y to
convince community to
add cosmic-extensions
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atmospheric 
Some results:
-spectrum
(includ.
syst.
errors)
10
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102
103
p[GeV]
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atmospheric 
Some results:
compared with some
nuclear interaction models predictions:
Models or primary rate not correct ?
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atmospheric 
Some results:
comparison with
models predictions:
(DELPHI)
Similar results from
L3+C & CosmoAleph
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All models fail to
predict highest
multiplicity
events ?!?!?
(assumption:
all primary are
Protons or Iron )
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Shower Tail: e.g. KASCADE
Forschungszentrum Karlsruhe
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KASCADE: array
Graz, 29.Nov.2007
Liquid scintillator plus
photmultiplier for e,
Lead-absorber plus
scintillator
for

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KASCADE some results
Measured secondary
flux vs. distance
from shower center
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KASCADE some results
Unfolding of
chemical
composition
for two
nuclearinteraction
models
==>
disagreement
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shower maximum
p or Fe Primaries ???
Difficult
to judge …
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AGASA
Similar principle as KASCADE,
but much larger area (less dense
sampling) ==> measure >>1015eV
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GZK-cutoff ?
Interaction of CR-protons with CMB:
pUHE + CMB --> + --> p + 0
--> n + +
Ethreshold ~ 1020 eV

~ 2x10-28 cm2
CMB
~ 400 cm-3
==> must come from
‘near’ sources (few Mpc)
15 evts
???
(i.e. local cluster ???)
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Fly’s Eye / HiRes
Completely different technique:
Measure fluorescence of shower
1981-1993
shower
particles
ionize air
==>
recombinat.
==>
fluorescence
light
(emitted in
all directions)
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Fly’s Eye / HiRes
First proposal:
1967
Major improvement:
stereo measurements
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Fly’s Eye / HiRes
HiRes does not
confirm high
trans-GZK flux
observed by
AGASA ?!!!!?!!!
Could be, one of the observation techniques
not well enough understood ????
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AUGER (south)
Hybrid:
- 1600 water tanks (cherenkov)
1.5 km separation between neighbours
3000km2
Status
Oct.2007
- 4x6 fluorescence telescopes
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AUGER (south)
One of 1600
‘ground stations’
3000 gallons
water,
3 Photomultipl.,
Electronics
shower particles hitting station:
produce cherenkov light in water;
signal incl. GPS-time transmit. to center
==> shower reconstruction
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AUGER (south)
One of 4x6
fluorescence
telescopes:
440 Photomultipliers
each
11m2 reflect.
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AUGER (south)
Science,9.11.07
black circles: all events >1018eV seen by AUGER (3o error)
red stars: position of nearby AGNs (<200Mpc)
==> seem correlated ==> nearby AGNs could be sources
of >1018eV particles ==> no problem with GZK
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even larger ...
Planned experiments:
-Telescope Array TA
(extend HiRes with
ground stations
similar to AUGER, but in north
-AUGER North
(3x larger than South)
(similar to TA ...
groups do not want to combine ...
-EUSO (@ISS)
search for fluorescence light from space
huge area, but light-pollution problematic
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EUSO
Look from ISS
to earth
Catch Fluores.&
Cherenkov light
from showers
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- History
- Direct CR Observations;
‘low’ Energy
- Indirect CR Observations;
‘high’ Energy
- Possible CR Sources
& Accelerators
Graz, 29.Nov.2007
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Key Questions
Location of sources:
nearby (solar system) ?
galactic? extragalactic? universal?
Distribution of sources:
- few bright point-like sources ?
- many faint sources/ diffuse ?
Type of sources:
- astrophysical (“stars”,fields) ?
- new physics (decay of heavy part.)?
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Main Problem
charged particles
are deflected by
all kinds of
magnetic fields
==>
can not be
traced back
to their origin
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Location of Sources
From p+X --> 0+Y , 0 -->  
Search for  with characteristic spectra
(mainly at rather low energies...)
==>
1) ~same CR everywhere in our Galaxy
==> (probably) not local/solar origin
2) far less CR in LMC (Large Magellanic Cloud)
==> not extragalactic/universal
origin
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Location of Sources
From magnetic field strengths:
==>
[for GeV … TeV energies]
1) CR can enter/escape solar system
==> (probably) not solar origin
2)
CR confined/shielded by galactic field
==> not extragalactic origin
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Location of Sources
Most probably, main component
of CR has galactic origin
(arguments not valid for highest energies:
- low contribution to 0 production
- can escape/enter galactic field ==>
highest energy CR probably extragal.)
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CR Power Requirements
Power needed to maintain galactic CR:
CR Energy-density: ~1eV / cm3
CR age (@few GeV): ~107 years
(CR density ~stable
>108 years )
L = (Volume)*(E-density)/(lifetime)
~ (15kpc)2(200pc) * 1eVcm-3 / 107y
~ 5 1040 erg/s = 5 1033 J/s
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Supernova (SN)
Already 1911 (before Hess showed extraterrestrial origin !)
Zwicky postulated SN as sources for CR !
Kinetic Energy emitted by typ-II SN:
Typically, ~10Mo ejected, v~5 108 cm/s
On average: 1 SN / 30 years in our Galaxy
==>
LSN ~ 3 1042 erg/s = 3 1035 J/s
==>
have to convert few% of kinetic SN
Energy into CR-Energy (reasonable ?)
(more than 99% of total SN Energy emitted in form of neutrinos ==>  Astronomy?!)
But SN do not accelerate to CR energies..
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Supernova Remnant (SNR)
Models show that (type-II)
Supernovae usually produce
two shock waves;
(shell-type SNR)
Energy loss at outer shock:
E1 = 2m(-v1v+v12)
Energy gain at inner shock:
E2 = 2m(v2v+v22)
E=E1+E2=2m(v12+v22+v(v2-v1))
E/E ~ (v2+v1)/v
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Supernova Remnant
Shock waves from SN have typical
lifetime  ~ 1000y
Energy gain per cycle: En+1=En(1+)
Escape Probab. per cycle: P
===> spectral index  ~ P/
...
===> Supernova Remnants (SNR) seem
excellent accelerators up to ~100 TeV
(B-field ~0.1G ==> larmor radius too large...)
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Neutron Star / Pulsar
Rotational Energy:
Energy loss
Erot ~ 1043 J
(deceleration):
E~ -0.3 1028J/s
Lifetime:
 ~ 108 y
#NS in Galaxy:
n ~ 106
==> total Energy emitted: nE ~ 1034J/s
compare ECR ~ 5 1033J/s
==> NS could maintain CR (if acceleration!)
(but Pulsars expected to emit this energy mainly by gravity waves..)
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Neutron Star / Pulsar
Fast rotation, huge B-field (1012-1015G)
If B tilted relative to 
==> spinning B-field --> strong E-field
max. value:
E ~
15
10 V/m
i.e. charged particle can gain 1000TeV/m !
NS can transform Erot into Ekin …
But: can CR escape NS region ???
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Neutron Star / Pulsar
Problem: huge B-field
==> Larmor-radius)
r[km] = E[MeV] / 30*B[G]
i.e. E = 100 TeV = 100 106 MeV
B = 1012G
r = 3 10-5km = 3mm !!!
==> particles can not escape ! (?)
But: ‘polar cap’ and ‘outer gap’ models ...
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Binary Neutron Star (BNS)
Macroscopic
mass-flow
from normal
(or giant)
star to
companion
Neutron Star
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Binary Neutron Star
Constant matter flux from star speeds up
the rotation of Pulsar ->‘millisecond Pulsar’
Known to emit ~1031 J/s
(per system)
in X-ray
If similar amount of Energy emitted in CR
==> few 100 Binaries could make major
contribution to total CR Energy
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Binary Neutron Star
Energy gain in Binary system:
Gravitational acceleration of proton:
RNS
E = -∫G mpMNS/r2 dr = G mpMNS/RNS
Inf.
~ 70 MeV
But mass flow >>1030 protons / second
==> huge total energy to be emitted
ev. secondary acceleration in shockwaves?
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Pulsar Wind Nebula (PWN)
Many Supernove remnants look not shell-type,
but rather chaotic (e.g. Crab)
Shell structure disturbed by outflow from
central pulsar
But shock waves still exist (or even enhanced)
==> PWN cosmic accelerators like SNR, but
also possibility for additional processes at NS
PWN from old pulsars could also collide with far
away clouds ==> shock waves ==> acceleration
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Starburst Regions (SB)
Galactic regions with high gas density:
==> many new stars created locally
==> high star density
==> combined stellar wind ?
==> many heavy stars
==> many SN / Pulsars / Binaries
==> stronger CR flux than average ???
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Active Galactic Nucleii (AGN)
Mass flow into huge black hole (M~109m)
in the center of a large galaxy
(black hole in center of our galaxy: M~2.5 106m)
Accretion disk and two
jets observed in
several AGNs
(jets > megaparsec ! )
‘Blazar’: jet pointing
to observer
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Starburst Galaxies
Galaxies with very high star-forming rate
(probably: high density/turbulent gas
regions induced by recent galaxy-collision)
==> much higher CR flux, high leakage ???
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Gamma Ray Bursts (GRB)
-Very short flash of extremely high X-ray flux
[highest energy phenomena since Big Bang...]
-Observe: ~1 GRB/day
-Extragalactic Origin many have huge redshifts
One GRB class seems correlated with SN
(---> Black Hole ?)
Other models: - Neutron Star mergers;
- Black Hole mergers;
- …
Enormous energy released, but not known if also
able to accelerate to CR energies ...
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Galaxy Clusters
High density of (large) Galaxies
==> combined ‘Galactic Wind’ could form
intense shock waves with IGM
==> high extragalactic CR flux ???
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Cosmic Accelerators
Problem:
What is accelerating?
But also:
Why so little
structure in
CR spectrum ???
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Cosmic Accelerators
Different classes of accelerators might
act on completely different time scales:
Typical values:
GRB:
AGN (flares):
SNR:
Neutron Stars/PWN:
~10-7 y (if accelerator)
~10-3 y
~103 y
~107 y
(remind: CR flux featureless and ~stable since 108 y)
(probably also different energy scales ....)
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Conclusion
• CR were (and still are) important tools to
investigate physics at unprecedented
energy
• learned a lot about the physics of CR
since their discovery
• many important experiments going on
• but still many open questions and much
room for good peoples with brilliant ideas
[ ?!!? entering ‘decade of astro-particle physics’ ?!!? ]
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