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38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 1
Galactic Cosmic Rays
Igor V. MoskalenkoStanford & KIPAC
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 2
Contents
Brief introduction to propagation of CRs Direct measurements Indirect measurements: diffuse gamma-ray emission CR in other normal galaxies
Leptons in the heliosphere (Nicola Giglietto’s talk)
GALPROP: New and free service “webrun”. Registered users can run the considerably improved version of GALPROP on our new cluster (~200 cores and Terabytes of storage) using the Web interface. Goes on-line in the first week of August
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 3
Introduction
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 4
CR Propagation: Milky Way Galaxy
Halo
Gas, sources
100
pc 50 kpc
4-12
kp
c
0.1-0.01/ccm
1-100/ccm
Intergalactic space
1 kpc ~ 3×1021 cm
R Band image of NGC8911.4 GHz continuum (NVSS), 1,2,…64 mJy/ beam
Optical image: Cheng et al. 1992, Brinkman et al. 1993Radio contours: Condon et al. 1998 AJ 115, 1693
NGC891
Sun
“Flat halo” model (Ginzburg & Ptuskin 1976)
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 5
CRs in the Interstellar Medium
e±
PHe
CNO
X,γ
gas
gas
ISRF
e+-
π+-
P_
LiBeB
ISM
•diffusion •energy losses •diffusive reacceleration •convection •production of secondaries
π 0
IC
bremss
ACEhelio-modulation
p
42 sigma (2003+2004 data)
HESS
SNR RX J1713-3946
PSF
B
HeCNO F
lux
20 GeV/n
CR species: Only 1 location modulation
π+-
PAMELA
BESS
Fermi
HESS
Chandra
WIMPannihil.
P_
P, X,γ
synchrotron
e±
e±
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 6
Elemental Abundances: CR vs. Solar System
CR abundances:
ACE
Solar system
abundances
LiBe
B
CN
O
F
F
e
ScTi
V
CrM
n
Si
C
l
A
l
“input”
“output”
Cosmic ray vs. solar system abundances, normalized to Si=100
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 7
Secondary/primary nuclei ratio & CR propagation
Using secondary/primary nuclei ratio (B/C) & radioactive isotopes (e.g. Be10): Diffusion coefficient and its index Galactic halo size Zh
Propagation mode and its parameters (e.g., reacceleration VA, convection Vz) Propagation parameters are model-dependent
Zh increase
Be10/Be9
Typical parameters (model dependent):D ~ 1028 (ρ/1 GV)α cm2/sα ≈ 0.3-0.6Zh ~ 4-6 kpc; VA ~ 30 km/s3
Inte
rste
llar
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 8
Secondary to primary nuclei ratios: B/C ratio
The B/C ratio <30 GeV/n measured by Pamela is consistent with earlier measurements (no surprises)
Statistical errors only Sparvoli’09
PAMELA Very preliminary!
The propagation models’ predictions differ at high energies which will allow to discriminate between them when more accurate data are available
CREAM
Ahn+’08
0.3
0.6
models tuned to the data
differentmodel predictions
0.5
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 9
Being tuned to one type of secondary/primary ratio (e.g. B/C ratio) propagation models should be automatically consistent with all secondary/primary ratios:
sub-Fe/FeHe3/He4
pbar/p
Secondary to primary nuclei ratios: sub-Fe/Fe
Jones+’01
(Sc+Ti+V)/Fe
ATIC
Ti/Fe
The rise in Ti/Fe ratio above ~100 GeV/nucleon is inconsistent with B/C ratio. Measurements of sub-Fe/Fe ratio is more challenging because of the smaller flux and charge is harder to discriminate
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 10
Diffusion coefficient in different models
Plain diffusion
DiffusiveReacceleration(Kolmogorov)
Reaccelerationwith damping
~R0.6
~β-3
extrapolation
Ptuskin+’06
The diffusion coefficient is model-dependent and is derived from secondary/primary nuclei ratio below ~100 GV
It is extrapolated above this energy
data
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 11
Energy losses of nucleons
The ionization and Coulomb losses are calculated for the gas number density 0.01 cm-3
The energy losses by nucleons can be neglected above ~1 GeV
Nuclear interactions are more important
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 12
Total inelastic nuclear cross sections
Ekin, MeV/nucleon
The inelastic cross section gives a probability of interaction
Rises with the atomic number as ~A2/3
As the result of interaction the original nucleus is destroyed
Wellisch & Axen 1996
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 13
Effective propagation distance: LE nuclei The interaction time scale at ~1 GeV – 1 TeV:
τ ~ L/c ~ [σnc]-1 ~ 3×1013/[0.25 (A/12)2/3] s ~ 3×106 yr (A/12)-2/3
σCarbon(A=12) ≈ 250 mb
The diffusion coefficient (4 kpc halo):
D ~ 3×1028 R1/2 cm2/s, R – rigidity in GV
Effective propagation distance:
<X> ~ √6Dτ ~ 4.5×1021 R1/4 (A/12)-1/3 cm ~ 1.5 kpc R1/4 (A/12)-1/3
Helium: ~ 2.1 kpc R1/4
Carbon: ~ 1.5 kpc R1/4 0.36% of the surface area (25 kpc radius)
Iron: ~ 0.9 kpc R1/4 0.16%
(anti-) protons:~ 6 kpc R1/4 5.76%
γ-rays: probe CR p (pbar) and e± spectra in the whole Galaxy ~50 kpc across
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 14
Direct probes of CR propagation
Direct measurements probe a very small volume of the Galaxy
The propagation distances are shown for rigidity ~1 GV
50 kpc
pC
Fe
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 15
Energy losses of electrons
The ionization and Coulomb losses are calculated for the gas number density 0.01 cm-3
Energy density of the radiation and magnetic fields 1 eV cm-3
(Thomson regime)
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 16
Effective propagation distance: HE electrons
The energy loss time scale (IC) at ~1 GeV – 1 TeV:
τ~ 300 E12−1 kyr ~ 1013 E12
−1 s; E12 – energy in TeV
The diffusion coefficient:
D ~ (0.5-1)×1030 E121/2 cm2/s
Effective propagation distance:
<X> ~ √6Dτ ~ 5×1021 E12−1/4 cm ~ 1 kpc E12
−1/4
~ a few kpc at 10 GeV
The cutoff energy of the electron spectrum ~1 TeV can be used to estimate the distance to the local HE electron sources: ≥ a few 100 pc.
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 17
Direct probes of CR propagation
Direct measurements probe a very small volume of the Galaxy
The propagation distances are shown for nuclei for rigidity ~1 GV, and for electrons ~1 TeV
50 kpc
p, 10 GeV eC
Fe, TeV e
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 18
Fermi/LAT PAMELA
PAMELA
A Constellation of CR and gamma-ray (also CR!) instruments
pbar
đ,α
e+
e-
p
He
Z≤8
8<Z≤28
Z>28
WIMPs
1 MeV/n 1 GeV/n 1 TeV/n
TIGER
BESS-Polar
TRACERHEAO-3
Fermi/LAT
BESS-Polar
AMS-I
ACE
HESSMagicMilagroVeritas
Integral
COMPTEL
EGRET
BESS-Polar
ATICCREAM
AM
S-I
HEATWMAP
CAPRICEanti-
mat
ter
mat
ter
SU
SY
−
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 19
Direct measurements
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 20
Recent experiments in cosmic rays
ATIC electrons (Chang+2008): 360+
PPB-BETS electrons (Torii+2008): 150+
Fermi LAT electrons (Abdo+2009): 310+
HESS electrons (Aharonian+2008, 2009): 280+
PAMELA positron fraction (Adriani+2009): 530+
leptons in CRs total: 1600+ citations in ~2 years!
PAMELA antiprotons (Adriani+2009): 240+ citations
BESS program (only journal papers): 1000+ citations
Of course, most of citations are coming from particle physics
★ using NASA ADS/June
2010
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 21
Positron fraction
The excess in the CR positron fraction relative to the predictions of secondary production models is confirmed by Pamela and extended to higher energies (up to ~100 GeV)
Additional positron component?
Charge sign dependence below ~10 GeV is expected
Adriani+’08
Solar modulation
GALPROP
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 22
Antiprotons
Antiprotons in CRs (BESS, Pamela) <200 GeV are in agreement with secondary production
PAMELA − GALPROP- - Donato+’01
− GALPROP… Donato+’09- - Simon+’98
Adriani+’10
Adriani+’10
PAMELA
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 23
Fermi measurements of leptons in CR
What’s here?
HESS
Fermi
Recently extended down to 7 GeV High statistics: ~8M events (7 GeV – 1 TeV) in
1 year Errors dominated by systematic uncertainties No evidence of a prominent spectral feature Analysis of events with high energy resolution
in progress to confirm spectral shape
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 24
Interpretation of CR electron data CR electron spectrum is consistent
with a single power-law with index -3.05
Can be reproduced well by the propagation models
Multi-component interpretation is also possible– Dark matter contribution– Astrophysical sources (SNR,
pulsars)– …
The key to understanding the electron spectrum (local vs global) is the origin of the positron excess and the diffuse gamma-ray emission
Kobayashi+’03
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 25
CR protons & He The CR proton and He spectra by
Pamela agree well with previous measurements
He spectrum is significantly flatter (~0.13 in index), but consistent with the proton index within the error bars
A hint on their different origin? No surprises for production of
secondary particles and diffuse gammas
protons He
PAMELA
Picozza’09
H: -2.752±0.071
He: -2.624±0.122
IM+’02
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 26
p and He spectral hardening at HE
Statistically significant spectral hardening and heavier composition at HE is reported by ATIC and confirmed by CREAM
Panov+’09
Ahn+’10
CREAM
ATIC
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 27
Heavy nuclei at high energies
Ratios of the mostly primary nuclei are independent on the energy pointing to a similar origin and the same acceleration mechanism
The spectral slopes of He and heavier nuclei are the same at HE and flatter than protons
A significant fraction of N is secondary – steeper spectrum; about 10% is primary
Ahn+’10
Ahn+’10
C/OCREAM
Ne/O
Si/O
N/O
Mg/O
Fe/O
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 28
Good
Xsections
Well-known
Differences in models
CR source isotopic abundances
The first time that a realistic propagation model (GALPROP) has been used to derive isotopic source abundances !
Two K-capture isotopes are present in the sources! -- 41Ca*, 53Mn*
Could tell us about the origin of CRs -- supports “volatility” hypothesis, but needs more analysis
15N33S
55Mn
41Ca*
53Mn*40Ca
22Ne
20Ne
32S
F
P
ScTiV
Solar systemReaccelerationPlain diffusion
IVM+’07
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 29
Cosmic ray sources
Some isotopes in CR sources are more abundant than in the solar system
May indicate that ~20% of CR particles are coming from WR star winds
Binns+’05
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 30
Heavy Nuclei in CRs
Produced in SN explosions Abundances drop quickly with ZLocal: very large inelastic cross section – small effective propagation distances
Nucleus Charge
Fe
Wiedenbeck+2007
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 31
The origin of cosmic rays
Cosmic ray acceleration seems to prefer refractory elements over volatile and does not depend on FIP, although most of refractory elements also have low ionization potential
Mixed with 20% of the WR wind outflow, the CR source composition/Solar system ratio shows a clear trend: ~A2/3 for volatile and ~A for refractory elements
This dependence is yet to be understood
TIGER
Rauch+’09
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 32
Sources of high energy cosmic rays
A similar trend appears also at high energy, although with larger error bars
A single acceleration mechanism for LE and HE cosmic rays?
CREAM
Ahn+’10
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 33
Fermi-LAT: First 3 Months Skymap (Counts)
Indirect mearurements:
Diffuse gamma-ray emission
The diffuse emission is the brightest source on the sky: ~80% of all photons
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 34
Geminga pulsar
Milagro C3
Pulsar (AGILE/Fermi)
MGRO 2019+37
Fermi Pulsar
SNR g Cygni
Fermi Pulsar
HESS, Milagro, Magic
Fermi Pulsar
Milagro (C4)
3EG 2227+6122
Boomerang PWN
SNR IC433
MAGIC, VERITAS
Radio pulsar
(new TeV source)
unID
(new TeV source)
unID
(new TeV source)
Fermi Pulsar
MGRO 1908+06
HESS 1908+063
SNR W51
HESS J1923+141
G65.1+0.6 (SNR)
Fermi Pulsar (J1958)
New TeV sources
G.Sinnis’09
Milagro: TeV observations of Fermi sources
Many γ-ray sources show extended structures at HE – thus they are also the sources of accelerated particles (CRs)
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 35
Fermi-LAT: diffuse gammas
Conventional GALPROP model is in agreement with the Fermi-LAT data at mid-latitudes (mostly local emission)
The EGRET “GeV excess” is not confirmed This means that we understand the basics of cosmic ray
propagation and calculate correctly interstellar gas and radiation field, at least, locally
model
Abdo+’09
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 36
Diffuse emission at low- to high Galactic latitudes
Mid-latitudes
Low latitudes
High latitudes
The GALPROP predictions agree well with the LAT data
Pion-decay and inverse Compton emission are two dominant components – allow us to probe the average CR proton and electron spectra along the line of sight
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 37
Diffuse Gammas – Local Spectrum
The spectrum of the local gas, after the subtraction of the IC emission, agrees well with the GALPROP predictions
Confirms that the local proton spectrum is similar to that derived from direct measurements
Abdo+’09
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 38
Milky Way as electron calorimeter Calculations for Zhalo= 4 kpc
Leptons lose ~60% of their energy γ-rays: 50-50 by nucleons and by leptons
Total gamma rays1.6%
Neutral pions0.85%
Synchrotron
0.35%
Bremsstrahlung
0.15%
Inverse Compton
0.58%
Primaryelectrons
1.41%
Primary nucleons98.6%
Cosmic rays7.90×1040 erg/s
Secondaryleptons
e+: 0.33% e−: 0.10%
Ionizationlosses
1%
0.06% (13.5%) 0.09% (6.6%)
0.1% (21.1%) 0.5% (34.8%)
0.06% (13.4%) 0.29% (20.8%)
0.16% (34.6%
) 0.59
% (
41.4
%)
* The percentages in brackets show the values relative to the luminosity of their respective lepton populations
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 39
Other normal galaxies
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 40
Cosmic rays in other normal galaxies (LMC)
After background subtraction
Milky Way
LMC
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 41
Starburst Galaxies: M82, NGC 253
The relationship between the gas mass, SNR rate, and gamma-ray luminosities in normal galaxies: LMC, Milky Way, M82, NGC 253
LMC
NGC 253M82
MW
38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 42
Thank you !
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