COSMIC RAYS IN THE MILKY WAY &

COSMIC RAYS IN THE MILKY WAY &

OTHER GALAXIES

IGOR V MOSKALENKO − STANFORD

The discovery of cosmic rays

!  Victor Hess, an Austrian scientist, took a radiation counter (a simple electroscope) on a balloon flight

!  He rose to 5200 m (without oxygen) and measured that the amount of radiation increases as the balloon climbed

!  Hess correctly concluded that the ionization was caused by highly penetrating radiation coming from outside the atmosphere

!  The results by Hess were later confirmed by the

Victor Hess flight on August 7, 1912

Nobel Prize: 1936

Hess Kolhörster

High energy gamma-ray emission processes

!  pp −> π

(2γ)+X − neutral pion production and decay

!  Inverse Compton scattering

!  Bremsstrahlung π

p p p

p

π

γ γ

γ

γ

e

e p

e γ

γ

hν

Fermi-LAT skymap >1 GeV, 48 months

4-year sky map, >1 GeV, front converting (best psf) (4.52M events)

!  LAT: ~275B triggers, 225M Source class events

!  GBM: >1000 GRBs

!  shows where accelerated particles meet targets (gas, photons)

!  ~80% of the emission is diffuse

!  our Galaxy provides the best opportunity to study CRs: direct and indirect measurements with

excellent resolution

Cosmic Scales

parsec 10^-10 10^-9 10^-8 10^-7 10^-6 10^-5 10^-4 10^-3 10^-2 10^-1 10⁰ 10¹ 10² 10³ 10⁴ 10⁵ 10⁶ 10⁷ 10⁸ 10⁹ 10¹⁰

3 000 km

30 000 km

300 000 km

3✕10⁶ km

3✕10⁷ km

2 AU

20 AU

200 AU

2 000 AU

0.1 pc

1 pc

10 pc

100 pc

1 kpc

10 kpc

100 kpc

1 Mpc

10 Mpc

100 Mpc

1 Gpc

10 Gpc

Proxima Centauri Sirius

Vega

Antares Milky Way

Andromeda Galaxy (@0.8 Mpc)

Local Group

Fermi-LAT skymaps, 48 months

E>1 GeV

!  Fewer sources at high energies

!  Less diffuse emission

E>10 GeV

Fermi-LAT skymaps, 48 months

!  Fewer sources at high energies

!  Less diffuse emission

!  Interesting physics

Cosmic rays from supernovae (1934)

! “…production of

cosmic rays is related to some sporadic

process, such as the flare-up of a super- nova…”

“If cosmic rays come from super-novae their intensity in points far away from any individual super-nova will be

essentially independent of time...”

“We have tentatively suggested that the super-nova process represents the

transition of an ordinary star into a

Local emissivities

!  Local gamma-ray emissivities derived from observations of the local gas clouds are consistent with the direct CR measurements

!  Show intensity variations due to errors in gas mass estimates, gas

composition, or true CR intensity variations

!  Morphology of γ-ray emission coincides well with shocked H

Fermi-LAT observations of SNRs IC443 & W44

IC443

5 − 50 GeV

W44

2 − 10 GeV

clouds

Abdo+2010

•  Low-energy cut off at half the π

mass

•  Clear evidence for SNR as hadronic acceleration sites

proton spectra

Fermi-LAT spectra of IC443 & W44:

π ⁰ decay γ-rays

e

X,γ

gas

gas ISRF

e

^- π

^- ISM

π

IC bremss

helio-modulation ACE

42 sigma (2003+2004 data)

HESS

PSF

B

F lux

20 GeV/n

CR species:

"  Only 1 location

"  modulation

π

^-

PAMELA BESS

Fermi HESS

Chandra

X,γ

synchrot ron

e

e

GALPROP solar modulation

CRs in the interstellar medium

AMS-02

Direct probes of CR propagation

50 kpc

p, 10 GeV e C Fe, TeV e

Effective propagation distance:

<X> ~ √6Dτ ~ 4.5×10

R

(A/12)

cm ~ 1.5 kpc R

(A/12)

Helium: ~ 2.1 kpc R

Carbon: ~ 1.5 kpc R

- 0.36% of the surface area Iron: ~ 0.9 kpc R

- 0.16%

(anti-) protons:~ 6 kpc R

- 5.76%

Electrons ~ 1 kpc E

γ-rays: probe CR p (pbar) and e± spectra in the whole Galaxy ~50 kpc across

!  Direct measurements probe a very small volume of the Galaxy

!  Light & heavy nuclei probe different propagation volume

!  The propagation distances are

shown for nuclei for rigidity ~1

GV, and for electrons ~1 TeV

Original motivation

!  Pre-GALPROP (before ~1997)

#  Many models, each with a purpose to reproduce data of a single instrument

#  Many different simplifying assumptions – hard to compare

#  Leaky-box type models: simple, but not physical

#  No or few attempts to make a self-consistent model

!  GALPROP model – >17 years of development

!  One Galaxy – self-consistent modeling

#  The key concept underlying the GALPROP code is that various kinds of data, e.g., direct CR measurements including primary and secondary nuclei, electrons and positrons, γ-rays, synchrotron radiation, and so forth, are all related to the same astrophysical components of the Galaxy and hence have to be modeled self-consistently

!  As realistic as possible

#  The goal is for GALPROP-based models to be as realistic as possible and to

make use of available astronomical information, nuclear and particle data,

with a minimum of simplifying assumptions

CR Propagation: Milky Way Galaxy

Halo 0.1-0.01/ccm

Intergalactic space

1 kpc ~ 3×10

cm

Optical image: Cheng et al. 1992, Brinkman et al. 1993 Radio contours: Condon et al. 1998 AJ 115, 1693

NGC891

Sun

“Flat halo” model (Ginzburg & Ptuskin 1976)

Transport Equations ~90 (no. of CR species)

Secondary/primary nuclei ratio & CR propagation

Using secondary/primary nuclei ratio (B/C) & radioactive isotopes (e.g. Be

):

!  Diffusion coefficient and its index

!  Galactic halo size Z

!  Propagation mode and its parameters (e.g., reacceleration V

, convection V

)

!  Propagation parameters are model-dependent

Typical parameters (model-dependent):

D ~ 10

(ρ/1 GV)

cm

/s α ≈ 0.3-0.6

Z

~ 4-6 kpc; V

~ 30 km/s

Zh increase

Be

/Be

Components of GALPROP

!  Detailed gas distribution from HI and CO gas surveys (energy losses from ionization, bremsstrahlung; secondary production; γ- rays from π ⁰ -decay, bremsstrahlung)

!  Interstellar radiation field (inverse Compton losses/γ-rays for e ^± )

!  B-field model

!  Nuclear & particle production cross sections + the reaction network (cross section database + LANL nuclear codes + phenomenological codes)

!  Cosmic ray source distribution(s)

!  Propagation, diffusive acceleration, convection

!  Numerically solve transport equations for all cosmic ray species (stable + long-lived isotopes + pbars + leptons ~90) in 2D or 3D

!  Derive the propagation parameters corresponding to the assumed

transport phenomenology and source distribution

Computing cluster

http://galprop.stanford.edu

500+ cores:

!  Intel Xeon 4×32 cores

#  384 GB shared memory each

!  Intel Xeon Phi coprocessor 4×2 cards

!  AMD Opteron 3×64 cores

#  256 GB shared memory each

!  6174 AMD Opteron 4×48 cores

#  128 GB shared memory each

!  Web server

!  Data storage (12 TB RAID0)

!  Infiniband link (10 Gbit/s)

Large scale study of the diffuse emission

IC

π

Brems

!  “Conventional model”: CR spectra are consistent with local measurements (CR nuclei, Fermi

electrons)

!  GALPROP code with diffusion-reacceleration model for CR propagation

!  Propagation parameters - fixed from CR data

!  Grid of 128 models covering plausible

confinement volume, CR source distributions, etc.

!  Corresponding model sky maps compared with data using maximum likelihood

!  Iterative process since the model parameters (Xco, H I) depend on outcome of the fit

!  A massive Fermi-LAT study – ApJ 750 (2012) 3

uniform

AMS-02 ! CERN ! Apr 15, 2015 :: IVM 21

Diffuse emission skymap

!  Observed Fermi-LAT

counts in the energy range 200 MeV to 100 GeV

!  Predicted counts calculated using GALPROP

reacceleration model tuned to CR data

!  Residuals (Obs-Pred)/Obs

~ % level, ~10% in some places

– 55 –

Fig. 5.— Upper panel: observed Fermi–LAT counts in the energy range 200 MeV to 100 GeV used in this paper. Lower panel: predicted counts for model

S

4

20

150

5 in the same energy range.

To improve contrast we have used a logarithmic scale and clipped the counts/pixel scale at 3000.

The maps are in Galactic coordinates in Mollweide projection with longitudes increasing to the left and the Galactic centre in the middle.

Observed

Predicted

Spectrum and profiles

!  Components of the model

#  Neutral pion emission from gas H

, H ^I , H ^II

#  Inverse Compton

#  Bremsstrahlung

#  Detected sources

#  Isotropic emission

Large scale study: residuals

!  Agreement for models is overall good, but features are visible in residuals at

~% level

!  Difference between illustrative models shown in right maps : structure due to

variations of model parameters

!  Models details:

2: SNR

4

20

150

5 44: Lorimer

6

20

∞

5 93: Yusifov

10

30

150

2 119: OB

8

30

∞

2

Model 2

93

44

119

NASA press release

!  Models reproduce the main features of the diffuse emission quite well

!  Discrepancies between the physical model and high-resolution data (residuals) are the gold mines of new phenomena!

!  Every extended source and/or process that is not included into the model pops up and

exposes itself as a residual

Fermi-LAT: emissivity gradient in the Galaxy

!  Radial profile with Galactocentric radius of the emissivity integrated between 200 MeV and 10 GeV. Black dots/horizontal bars mark the ranges in kinematic distance encompassing the Gould Belt, the main part of the local arm, the

Perseus and outer arms.

Abdo+’2010

GALPROP

Milky Way in the global picture

! The Milky Way is the nearest example of a spiral galaxy

! It provides the best opportunity to study ongoing star

formation, cosmic rays, and related processes in the ISM

! Important reference point

! Baryonic content of the Universe is dominated by ``normal'’

galaxies

! ~70% are spiral galaxies

Milky Way as an electron calorimeter

!  Calculations for Z

= 4 kpc

!  Leptons lose ~60% of their energy

!  γ-rays: 50-50 by nucleons and by leptons

Total gamma rays 1.6%

Neutral pions 0.85%

Synchrotron 0.35%

Bremsstrahlung 0.15%

Inverse Compton 0.58%

Primary electrons

1.41%

Primary nucleons 98.6%

Cosmic rays

7.90×10

erg/s

Secondary leptons e

: 0.33%

e

: 0.10%

0.06% (13.5 %) 0.09% (6.6%)

* The percentages in brackets show the values relative to the luminosity of their respective lepton populations

Strong+’2011

Starforming Galaxies

Cosmic Rays as a Universal Phenomenon

!  γ-ray luminosity vs. IR

luminosity for normal galaxies detected with Fermi-LAT

!  The γ-ray luminosity scales linearly (index ~1.1) with the total emission of hot stars reprocessed by dust − a tracer of star formation

!  The ratio approaches the

calorimetric limit in star-burst galaxies

!  An evidence of the SNR-CR connection in normal star- forming galaxies

Thin target Thick target

calorimetric limit

Galactic cosmic rays in the solar system

!  Allows to reconcile direct & indirect observations

#  Test models of interactions

#  Calibration of the instrument

!  Detected sources:

#  The Earth (PRD 80, 122004, 2009)

•  The limb

•  Terrestrial γ-ray flashes

#  The Moon (ApJ 758, 140, 2012)

#  The steady Sun (ApJ 734, 116, 2011)

#  Solar flares

Direct measurements

Break in the CR p and He absolute fluxes

!  Preliminary AMS-02 data do nor show any spectral feature

Adriani+’2011

He p

!  Data from several experiments (BESS,

AMS-01, ATIC’2009, CREAM’2010,

PAMELA’2011) are all consistent and

indicate spectral hardening above ~100

GeV/nucleon

Fermi-LAT observations of the Earth’s limb

p

γ

Column density

Emission profile

>30 GeV

PSF

thin target:

68.4°≤θ≤70.0°

D if fus e em is si on dom ina te s

! Due to its proximity, the Earth is the brightest γ-ray source on the sky

! The emission is produced by the CR cascades in the atmosphere

! Most energetic γ-rays are produced by CRs hitting the top of the atmosphere at tangential directions (thin target)

γ-ray flux

>3.6 GeV

2 g cm

γ-ray flux

Inferred CR Proton Spectrum from

pp Model by Kachelrieβ & Ostapchenko (2012)

Index = 2.68 ± 0.04

Index

= 2.81 ± 0.11 E

= 302 ± 96 GeV Index

= 2.61 ± 0.08

SPL

BPL

March 28, 2014 W. Mitthumsiri Page 10 / 12

R

H L

I P

!  All scenarios are tuned to the data, except the Reference scenario

!  Scenarios L and H: the local source

component is calculated by the subtraction of the propagated Galactic spectrum from the data

!  The local source is assumed to be close to us, so no propagation;

only primary CR species

10^-1 1

Flux2.7 F(),GV1.7 cm-2 s-1 sr-1

1 10 10² 10³ 10⁴ 10⁵

R igidity , G V

Calculation R CR EAM ATIC-2 PAM ELA

p

He

10^-1 1

Flux2.7 F(),GV1.7 cm-2 s-1 sr-1

1 10 10² 10³ 10⁴ 10⁵

R igidity , G V

Calculation P CR EAM ATIC-2 PAM ELA

p

He

10^-1 1

Flux2.7 F(),GV1.7 cm-2 s-1 sr-1

1 10 10² 10³ 10⁴ 10⁵

R igidity , G V

Calculation I CR EAM ATIC-2 PAM ELA

p

He

10^-1 1

Flux2.7 F(),GV1.7 cm-2 s-1 sr-1

Calculation L CR EAM ATIC-2 PAM ELA

p=Galactic+local

Galactic p local p

He=Galactic+local Galactic He

local He 10^-1

1

Flux2.7 F(),GV1.7 cm-2 s-1 sr-1

Calculation H CR EAM ATIC-2 PAM ELA

p=Galactic+local

Galactic p local p He=Galactic+local

Galactic He local He

Propagation

Reference

Injection

Local LE Local HE

P and He spectra

Vladimirov+’2012, ApJ 752, 68

2 5

10

p/Hefluxratio

1 10 10² 10³ 10⁴ 10⁵

R igidity ,G V C alculation R C alculation P

C alculation I C alculation L C alculation H

PA M ELA A TIC -2 C R EA M Plain D iff.M odel

10^-3 10^-2 10^-1 1

p/p10-3

10^-1 1 10 10² 10³ 10⁴

E,G eV /nucleon C alculation R C alculation P

C alculation I C alculation L C alculation H

PA M ELA

D iff.-R eacc.M odel

10^-4 10^-3 10^-2 10^-1

Anisotropy,

10³ 10⁴ 10⁵ 10⁶

E,G eV Calculations

R, I, L and H Calculation P Diff.-Reacc. Model

More predictions

!  P/He ratio is tuned in all scenarios except Reference scenario

!  Predicted antiproton/proton ratio agrees with the existing data, but exhibits different behavior at >100 GeV

!  Only scenario P agrees with the data on CR anisotropy

!  Only scenario L can explain the sharp break in the p, He spectra

!  Await for more accurate data

B/C ratio

!  P-scenario is predicting an upturn in the B/C ratio at

~100 GeV/n (~200 GV)

1 TeV

New measurements of B/C ratio

PAMELA fit to the B/C ratio

!  Use GALPROP

!  Parameters from Vladimirov+’2012

!  Best fit index of the diffusion coefficient: δ = 0.4

!  No significant spectral features

<400 GeV/n (AMS-02)

E(GeV/n)

0.4 1 2 3 4 5 6 7 8 10 20 30 40 100

B/C

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

PAMELA AMS-02 (preliminary) Galprop

CREAM TRACER ATIC-2 HEAO AMS-01

E(GeV/n)

0.4 1 2 3 4 5 6 7 8 910 20 30 40 50 100

1.7 (GeV/n)-1 s sr)2 (m2.7 E×Flux

10-1

1

10 ^C

B

PAMELA Galprop CREAM TRACER ATIC-2 HEAO CRN

B & C spectra PAMELA

B/C ratio PAMELA

?

PAMELA data: rising positron fraction

!  PAMELA team reported a rise in the positron fraction compared to the “standard”

model predictions

!  “Standard” model:

#  Secondary production

#  Steady state

#  Smooth CR source distribution

Nature 458, 607 (2009)

IVM&Strong’1998

PAMELA

Adriani+’2009

AMS-02: Rise in the positron fraction

!  Asymptotically approaches a const ~0.15-0.2 ?

!  A cut off at HE ?

Nature 458, 607 (2009)

IVM&Strong’1998

Positron fraction: Astrophysical papers

!  Blasi 2009 “Origin of the positron excess in cosmic rays”

!  Blasi & Serpico 2009 “High-energy antiprotons from old supernova remnants”

!  Mertsch & Sarkar 2009 “Testing astrophysical models for the PAMELA positron excess with cosmic ray nuclei”

!  Shaviv+ 2009 “Inhomogeneity in cosmic ray sources as the origin of the electron spectrum and the PAMELA anomaly”

!  Delahaye+2010 “Galactic electrons and positrons at the Earth: new estimate of the proimary and secondary fluxes”

!  Stawarz+2010 “on the energy spectra of GeV/TeV cosmic ray leptons”

!  Lee+ 2011 “Explaining the cosmic ray e

/(e

+e

) and pbar/p ratios using a steady-state injection model”

!  Kachelriess+2011 “Antimatter production in supernova remnants”

!  Kachelriess & Ostapchenko 2013 “B/C ratio and the PAMELA positron excess”

!  Blum+ 2013 “AMS-02 results support the secondary origin of cosmic ray positrons”

!  Cholis & Hooper 2013 “Dark matter and pulsar origin of the rising cosmic ray positron fraction in light of new data from the AMS”

!  Erlykin & Wolfendale 2013 “Cosmic ray positrons from a local, middle-aged supernova remnant”

!  Berezhko & Ksenofontov 2013 “Energy spectra of electrons and positrons produced in supernova remnants”

!  Berezhko & Ksenofontov 2013 “Antiprotons produced in supernova remnants”

!  Cholis & Hooper 2014 “Constraining the origin of the rising cosmic ray positron fraction with the boron- to-carbon ratio”

!  Di Mauro+2014 “Interpretation of AMS-02 electrons and positrons data”

!  Mertsch & Sarkar 2014 “AMS-02 data confronts acceleration of cosmic ray secondaries in nearby sources”

!  Cowsik+2014 “The origin of the spectral intensities of cosmic ray positrons”

!  …

!  + Dark Matter paper >1000

Interpretations

!  Dark matter annihilation/decay

!  SNR shocks:

#  Galactic SNRs

#  Local SNR(s)

!  “Nested Leaky-Box” (SNRs)

!  Inhomogeneity of CR sources (SNRs)

!  “Model-independent estimates”

!  Photoproduction

!  Pulsars & Pulsar Wind Nebulae

ISM

Old friends − pulsars

!  Arons 1981 “Particle acceleration by

pulsars”

!  Harding & Ramaty 1987 “The pulsar contribution to

Galactic cosmic ray positrons”

!  Boulares 1989 “The nature of the cosmic- ray electron

spectrum, and

supernova remnant contributions”

“Therefore, the only role observed pulsars might play as direct cosmic ray sources is in providing positrons and electrons…”

3 components:

!  Secondary e

!  Primary e

from SNR

!  Primary e

from

pulsars

Reinvention of the Nested Leaky-Box − SNRs

!  Cowsik & Wilson 1974 “The nested Leaky-Box model for Galactic cosmic rays”

!  Berezkho+2003

“Cosmic ray production in supernova

remnants including reacceleration: The secondary to

primary ratio”

n = 1 cm

n = 0.3 cm

n = 0.003 cm

“In this paper we shall in addition take the effect of nuclear spallation inside the sources into account.

The energy spectrum of these source secondaries is harder than that of

reaccelerated secondaries.

Therefore it plays a dominant role at high

energies for a high-density ISM...”

“The ‘inner box’ of cosmic ray confinement,

corresponding to the region immediately surrounding the source, is assumed to have energy-dependent life time...”

B/C

Secondary production in SNR shock

E

F lux

E

Primary

shock γ~2-2.4

Secondary δ

γ~3-3.4 δ

!  Gas in the shock – target for p, A

!  Flatter spectrum of p, A – flatter spectrum of secondaries

!  Assume no energy losses

!  δ~0.3-0.7 – effect of IS propagation (no losses)

!  Same effect should be observed for any secondaries (pbars, B, e

)

!  Energy losses will modify the spectra of e

at low and high energies - depend on the environment

shock γ~2-2.4

δ

E

F lux

E

Sec

SNR

ISM Prim

Positron production in SNR shock

!  Old SNR ~10

yr

!  Leaky-box type propagation model:

#  Halo size ~3 kpc

#  D~10

(E/GeV)

cm

s

#  IC+sync energy losses

Blasi 2009

Antiproton production in SNR shock

!  Same model as in Blasi’2009

!  pbars/p ratio does not contradict to positron fraction

Blasi & Serpico 2009

Boron production in SNR shock - I

!  A model similar to Blasi & Serpico 2009

!  Proposed to distinguish between pulsar & SNR origin of the positron excess

!  Leaky-Box for Galactic propagation

!  Cross sections from Silberberg &

Tsao

!  Nearby SNR(s)

!  Data: HEAO-3, ATIC-2, CREAM

!  Predicts an upturn in the B/C ratio near ~100 GeV/nucleon

!  Ti/Fe is much less reliable than B/C:

#  Charge resolution at HE

#  Uncertain production cross sections

•  Model prediction

•  Contamination: production in the atmosphere & instrument

Mertsch & Sarkar 2009 B/C

Ti/Fe

Boron production in SNR shock - II

!  Test particle approach

!  Monte Carlo

!  B-field

#  Const turbulent field 1 µG

#  B=100 µG (t<240 yr), 0.05 µG after

!  T

~13 kyr

!  Interstellar propagation & cross sections − GALPROP

!  D=4.8×10

(E/10 GeV)

cm

s

!  Predicts flattening in the B/C ratio above ~1 TeV/nucleon

Kachelriess & Ostapchenko 2013

Restrictions on the models based on B/C data - I

!  Leaky-Box (ST cross sections) &

GALPROP

!  Use parameters of previous works (Blasi 2009, Mertsch & Sarkar 2009)

!  Interstellar propagation:

Leaky-Box δ=0.6, GALPROP δ=0.43, tuned to B/C below 30 GeV/n

!  Found that increase in Ti/Fe

(ATIC-2) is inconsistent with new B/C data

!  Problem:

#  B/C “background” shows flattening in LB model at HE

Cholis & Hooper 2014 Leaky-Box

GALPROP

?

Cholis & Hooper 2014

Restrictions on the models based on B/C data - II

!  Such a mechanism provides only ~25% of excess positrons unless they are produced in proton-rich SNR shocks (with deficit of heavier nuclei)

!  Antiprotons do not show any excess which makes “proton- rich” hypothesis unlikely

GALPROP Cholis & Hooper 2014

25%

Stochastic sources − I

!  Interstellar propagation &

cross sections − GALPROP

!  3-D stochastic mode of

GALPROP – 25 realizations of pulsar-like distribution

!  Model 2 is better, but Z

= 1 kpc may be too small (the source distribution does not play a role)

Mertsch & Sarkar 2014

Stochastic sources − II

!  A couple of more data points in the B/C ratio and/or antiproton spectrum at HE should be

enough to discriminate between models

Mertsch & Sarkar 2014

Nested Leaky-Box

Cowsik+2014

– 55 –

Fig. 5.— Upper panel: observed Fermi–LAT counts in the energy range 200 MeV to 100 GeV used in this paper. Lower panel: predicted counts for model

S

4

20

150

5 in the same energy range.

To improve contrast we have used a logarithmic scale and clipped the counts/pixel scale at 3000.

The maps are in Galactic coordinates in Mollweide projection with longitudes increasing to the left and the Galactic centre in the middle.

Fermi-LAT - Observed

Predicted ISM

Source

!  Sec. nuclei are produced near the sources

!  Positrons are produced in the ISM

!  Contradicts to observations of the diffuse emission – it would be very dim at low energies (<10 GeV)

!  Note also flat spectra (index −2) of starburst galaxies!

Current state

ISM

?% ?%

?%

?%

The question is not where excess positrons are produced – positrons are produced

everywhere

The correct question is “How much?”

Calculation of e

contribution by pulsars from the first principles is very difficult

Observations of pbars and secondary nuclei

(Boron) at HE should be able to answer this

question

Conclusion

100 years after the discovery of CRs they

continue to surprise us – thanks to the precise CR and gamma-ray measurements and

discoveries of the last decade.

More discoveries are right around the corner!