ultra high energycosmic rays:
theoretical aspects
Daniel De MarcoBartol Research InstituteUniversity of Delaware
2
plan
observations & open issues
origin of UHECRspropagation: the GZK
featuresmall scale anisotropiesUHECRs, -rays and s
3
indirect observation (EAS)direct observation
(1 particle per km2--century)
4
indirect observation (EAS)direct observation
(1 particle per km2--century)many joules in
one particleUHECR
5
UHECRs: observations
AGASAHiResAuger
spectrum
arrival dirs. low energy
composition
Ostapchenko, Heck 2005
arrival directions high energy AGASA
AGASA
6
AGASAHiResAuger
spectrum
composition
Ostapchenko, Heck 2005
UHECRs: observations
arrival dirs. low energy
arrival directions high energy AGASA
AGASA
two (separate) issuesproductio
nfor astrophysical accelerators it is challenging to accelerate particles to such high energies.
propagationGZK feature in the energy spectrum due to the interactions with the photons of the CMB
end of the CR spectrum at some
high energy
strong flux suppression around 5
x 1019eV
7
origin of UHECRsbottom-up top-down
• the energy flux embedded in a macroscopic motion or in magnetic fields is partly converted into energy of a few very high energy particles.
• Shock acceleration at either Newtonian or Relativistic shocks.
• Composition: nucleons (nuclei)• autolimiting: Emax ≤ Ze B L
8
hillas plot Emax ≤ Ze B L
Olinto 2000
Hillas 1984
accounting for energy losses the situation is even more difficult
lines: 1020 eV
9
origin of UHECRsbottom-up top-down
• the energy flux embedded in a macroscopic motion or in magnetic fields is partly converted into energy of a few very high energy particles.
• Shock acceleration at either Newtonian or Relativistic shocks.
• Composition: nucleons (nuclei)• autolimiting: Emax ≤ Ze B L
• particle physics inspired models• UHECRs are generated by the
decay of very massive particles mX » 1020 eV originating from high-energy processes in the early universe.
• Topological Defects or SMRP• flatter spectra• Composition: dominated by
photons• Constraints from the diffuse
gamma rays flux measured by EGRET around 100 GeV
10
propagation of UHECRs: protons
• redshift losses• pair production (Eth ~ 5x1017 eV) pUHE +CMB N + e+ + e-
• pion production (Eth ~ 7x1019 eV) pUHE +CMB N + high inelasicity (20 – 50%)GZK suppression:
loss length @ 5x1019 eV = 1 Gpcloss length @ 1020 eV = 100 Mpc
loss lengths
11
GZK feature: single sourcemodification factor: observed spectrum / injection spectrum
bump
suppression
12
similar conclusions for nuclei and gamma rays: CRs can not reach us at
UHE if theyare generated at distances larger
than about 100 Mpc(except neutrinos, violations of LI and so on)
if the sources are uniformly distributed in the universe we should expect a suppression in the flux of UHECRs
around 1020 eV
13
AGASA & HiRes
a factor 2 in
the flux
HiRes: GZK
AGASA: no GZK
AGASA claims noGZK at 4HiRes claims GZK at 4
actual discrepancies
more like~3 and ~2
DDM, Blasi, Olinto 2003, 2005
14
systematic errors (?)AGASA -15%
HiRes +15%agreement
at low energy
less disagreement at
high energyhow much??
~2DDM, Blasi, Olinto 2003, 2005DDM, Stanev 2005
15
som
e AG
ASA
spec
tra
DDM, Blasi, Olinto 2005
16
both AGASA and HiRes do not have enough
statistical power to determine if the GZK
suppression is there or not
17
auger:hybrid
detection
18
AGASAHiResAuger
19
Auger energy determination
1019eV
•reconstruct S(1000)•convert S(1000) to S38 using CIC curve
•convert S38 to energy using the correlation determined with hybrid data
20
Auger ICRC spectrum
444
17
21
small scale anisotropy
AGASA: 5 doublets + 1 triplet
22
AGASA 2pcf point sources (?)
see also Finley and Westerhoff 2003DDM, Blasi, Olinto 2005
23
AGASA multipletsB~<10-10 G resol.=2.5º
=2.6 m=0E > 4x1019 eV - 57 events
10-6 Mpc-3
10-5 Mpc-3 10-4 Mpc-3
DDM, Blasi 2004
24
sources characteristics
LCR = 6x1044 erg/yr/Mpc3 (E>1019 eV - from spectrum fits)
n0 = 10-5 Mpc-3 (from ssa)
Lsrc = 2x1042 erg/s (E>1019 eV)
are these ssa for real?•the significance of the AGASA result is not clear
•HiRes doesn’t see them•some internal inconsistency
25
P: 6 10-4 2 10-4
: 3.2 3.7
AGASA spectrumdiscrete sources
DDM, Blasi, Olinto 2005
26
arriv
al
dire
ctio
nsP~2 10-5
DDM
, Bla
si, O
linto
200
5
27
both the ssa and the spectrum measurement
need more statistics to beconclusive and reliable
28
galactic magnetic fieldregular + turbulent
• spiral on the plane• exponential decay
out of the plane (~1 kpc)
• ~2 G at Sun position• Lmax ~ 100 - 500 pc• Bt ~ 0.5 - 2 Breg• spectrum: (??)
kolmogorov, 5/3kraichnan, 3/2
RL(4x1019eV) = 20 kpcno big deflections except in the disk or in the center
sun
29
deflections in EGMF - 4x1019eV 110 Mpc
deflections>1o in less than 2% of
sky• self-similarity
>1o in less than 30% of sky up to 500 Mpc
Dolag at el. 2003: constrained simulation of the MF in the local universeMF in voids: 10-3-10-1 nGMF in filaments: 0.1-1 nG
Sigl et al. 2004: very similar approach, completely different results. Fields in voids higher by 2-4 orders of magnitude.
CR astronomy (maybe) possible
CR astronomy definitely impossible
30
UHECRs, neutrinos and gamma raysinteraction of
accelerated protons in the sources or during
propagation• the neutrino spectrum is
unmodified, except for redshift losses
• gamma rays pile up below the pp threshold on the CMB (~ few 1014eV)universe = calorimeter
Lee 1998
EGRET diffuse gamma ray flux(MeV - 100 GeV) produces a constraint on neutrino fluxes
31
Mannheim, Protheroe, Rachen 2000
EG p: E-2(thin)
max.EG pflux
p/ horizon ratio
from EG GR bg
CR bound on from astrophysical sources
Waxman & Bahcall 1998
EGCR spectrum:1019 - 1021eV
fraction of energy lost
fraction going in neutrinos
energy density of muon neutrinos
not valid for top-down sources,optically thick sources…
32
GZK neutrinos
rates per km3 water per year: 0.1-0.2
W&B
from neutron decay from neutronspion-production
Engel, Seckel, Stanev 2001
33
issues/questions for the future
•increase statistics above 1020eV: is the GZK feature present? (solve SD-FD discrepancy)
•increase statistics above 4x1019 eV to identify ssa and possibly determine density of sources
•measure chemical composition at low energy to determine where the G-XG transition is occurring and at high energy to understand the nature of UHECRs
•multifrequency observation of the sources