Galactic Cosmic Rays

38th COSPAR, Bremen – July 18, 2010 :: IVM/Stanford-KIPAC 1

Galactic Cosmic Rays

Igor V. MoskalenkoStanford & KIPAC


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


Introduction


CR Propagation: Milky Way Galaxy

Halo

Gas, sources

100

pc 50 kpc

4-12

kpc

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)


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 Fl

ux

20 GeV/n

CR species: Only 1 location modulation

π+-

PAMELA

BESS

Fermi

HESS

Chandra

WIMPannihil.

P_

P, X,γ

synchrotron

e±

e±

http://universe.gsfc.nasa.gov/astroparticles/programs/bess/BESSGroup1_2004.jpg


Elemental Abundances: CR vs. Solar System

CR abundances: ACE

Solar system abundances

LiBeB

CNO

F

Fe

ScTiV

CrMn

Si

Cl

Al

“input”

“output”

Cosmic ray vs. solar system abundances, normalized to Si=100


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


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


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


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


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


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


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


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


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)


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 E12

1/2 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.


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


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-PolarAMS-I

ACE

HESSMagicMilagroVeritas

Integral

COMPTELEGRET

BESS-Polar

ATICCREAM

AM

S-I

HEATWMAP

CAPRICEanti-

mat

ter

mat

ter

SUSY

−


Direct measurements


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


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


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


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


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


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

PAMELAPicozza’09

H: -2.752±0.071

He: -2.624±0.122

IM+’02


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+’10CREAM

ATIC


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


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


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


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


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


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


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


Geminga pulsarMilagro C3

Pulsar (AGILE/Fermi)MGRO 2019+37

Fermi PulsarSNR g CygniFermi Pulsar

HESS, Milagro, Magic

Fermi PulsarMilagro (C4)

3EG 2227+6122Boomerang PWN

SNR IC433MAGIC, VERITAS

Radio pulsar (new TeV source)

unID(new TeV source)

unID(new TeV source)

Fermi PulsarMGRO 1908+06HESS 1908+063

SNR W51HESS J1923+141

G65.1+0.6 (SNR)Fermi Pulsar (J1958)

New TeV sources

G.Sinnis’09

Milagro: TeV observations of Fermi sourcesMany γ-ray sources show extended structures at HE – thus they are also the sources of accelerated particles (CRs)


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


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


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


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


Other normal galaxies


Cosmic rays in other normal galaxies (LMC)After background subtraction

Milky Way

LMC


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


Thank you !

You are here

Documents

Galactic Cosmic Rays