leptons in cosmic rays:

HEAD 2010 – Mar.3, 2010 :: IVM/Stanford-KIPAC 1 IVM/Stanford-KIPAC 1 PAMELA Workshop, Rome/May 12, 2009

Igor V. Moskalenko (stanford/kipac)

Leptons in Cosmic Rays:

HEAD 2010 – Mar.3, 2010 :: IVM/Stanford-KIPAC 2

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

sec. production (GALPROP)


Cosmic ray electrons

A slope the CR electron spectrum can be easily reproduced in propagation models

Most interesting is the fine structure, if confirmed, and the cutoff at ~1 TeV

Latronico+’09

What’s here?


One good experiment is worth thousand theories…

ATIC electrons: 270+ PPB-BETS electrons: 150+ Fermi LAT electrons: 170+ HESS electrons: 100+ PAMELA positron fraction: 370+

leptons in CRs total: 1000+ citations in ~1 year!

PAMELA antiprotons: 150+ citations (in <1 yr) BESS program (only journal papers): 1000+ citations

Of course, most of citations are coming from particle physics★ using NASA ADS


An experiment in nature, like a text in the Bible, is capable of different interpretations.

— William Jones,1781

There is no deficit in interpretations of the PAMELA positron excess (Adriani+’08): 370+ papers since Oct 2008!– Various species of the dark matter (most papers)– Pulsars– SNRs– Microquasars– a recent GRB nearby– …

Perhaps we have to discuss a deficit of positrons, not their excess!

Unfortunately, >99.7% of these explanations are wrong …Because there is only one correct explanation


The Goal of This TalkTo discuss a place of recent leptonic

data in astrophysics of cosmic rays Some calibration issues A couple of words about heliospheric

modulation How well do we understand the

propagation of CRs? Lepton-specific issues


Calibration Issues


Fermi-LAT:the Earth’s albedoA test of on orbit calibration of the LAT can be done using the Earth limb albedo spectrum – produced by CR interactions with the Earth’s atmosphere(Abdo+’09).

The spectral index of the albedo is close to the spectral index of ambient CRs.


CR measurements and backgrounds

CR protons are the dominant background for positron detection

PAMELA people made a tremendous job by hunting down every proton (see Mirko’s talk)

See Marty’s summary

L.Baldini


Cosmic rays in the heliosphere


Charge-sign dependence The Parker magnetic field has opposite magnetic polarity above and below the helio-equator, but the spiral field lines are mirror images of each other.

M.Potgieter

Solar min

Solar max

This antisymmetry produces the drift velocity fields that affect the particles of opposite charge in different ways (converge on heliospheric equator or diverge from it).


Probes of propagation in the interstellar

medium

nuclei in cosmic rays diffuse Galactic γ-rays


Secondary/primary nuclei ratio & CR propagation

Using secondary/primary nuclei ratio (B/C) & flux:

• Diffusion coefficient and its index• Propagation mode and its parameters (e.g.,

reacceleration VA, convection Vz)• Propagation parameters are model-

dependent• Make sure that the spectrum is fitted as well

Radioactive isotopes:Galactic halo size Zh

Zh increase

Be10/Be9

Ek, MeV/nucleon

Parameters (model dependent):D~ 1028 (ρ/1 GV)α cm2/sα ≈ 0.3-0.6Zh ~ 4-6 kpcVA ~ 30 km/s

Boro

n/Ca

rbon

(B/

C)

Inters

tellar

Ek, MeV/nucleon


Radioactive secondariesDifferent size from different ratios…

Zhalo,kpc

ST

W

27Al+p26Al

In determination of the propagation parameters one has to take into account:

Errors in CR measurements (@ HE & LE)Errors in production cross sectionsErrors in the lifetime estimates

natSi+p26Al

W

STT1/2=?

W – Webber+ST – Silberberg & Tsao- - - – measured

• The error bars can be significantly reduced if more accurate cross sections are used

• Different ratios provide consistent parameters


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


PAMELA & CREAM: B/C ratioThe B/C ratio <30 GeV/n is measured by Pamela (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 (hopefully after CREAM V flight)

CREAM

Ahn+’08

Launched on Dec. 1, 2009, CREAM-V just finished its 3rd circle around the South Pole!


CR Protons & He

The CR proton and He spectra by Pamela agree well with previous measurements

No surprises for production of secondary particles and diffuse gammas

protonsHe

PAMELAPicozza’09

H: -2.752±0.071

He: -2.624±0.122

IM+’02


Antiprotons Antiprotons in CRs

(BESS, Pamela) <100 GeV are in agreement with secondary production

PAMELA

Picozza’09

Picozza’09

|Ptuskin+’06


Fermi-LAT: diffuse gammas Conventional GALPROP model is in agreement

with the Fermi-LAT data at mid-latitudes (mostly local emission)

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


Spectrum of the Galactic diffuse emission, longitude and latitude profiles

CR intensities are adjusted by a factor: protons – 1.3, electrons - 1.5

|b|≤5,°|l|≤30°

|b|≤5°

|l|≤60°

1.2 GeV ≤ E ≤ 1.6 GeV

Loop ITotal diffuseBright sourcesπ0-decayInverse ComptonBremsstrahlungIsotropic component PRELIMINARY


Lepton-specific issues


Kobayashi+’03

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 in understanding of the electron spectrum (local vs global) is the origin of the positron excess and the diffuse gamma-ray emission


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)


Effective propagation distance The energy loss time scale (IC) at ~1 GeV – 1 TeV:

τ~ 300 E12-1 kyr ~ 1013 E12

-1 cm; E12 – energy in TeV

The diffusion coefficient: D ~ (0.5-1)x1030 E12

1/2 cm2/s

Effective propagation distance:<X> ~ √6Dτ ~ 5x1021 E12

-1/4 cm ~ 1 kpc E12-1/4

We do not know the exact energy of the spectral cutoff and electron spectrum at the source, so the distance to the local sources of VHE electrons could be ≥ a few 100 pc.


Solar system in the Milky Way

The solar system is located in the inter-arm region – a very safe place!


(Some) Important questions to answer

How large is the positron fraction at HE (PAMELA)?– Identifies the nature of sources of primary positrons

If SNRs are the sources of primary positrons, this should also affect antiprotons and secondary nuclei @ HE…– Measure pbars and secondary nuclei (PAMELA, CREAM…)

How typical for the local Galactic environment is the observed positron fraction?– If this is the typical fraction, the sources of primary positrons are

distributed in the Galaxy (could be pulsars, SNRs, or DM)– If this fraction is peculiar then there is a local source or sources of

primary positrons Fine structure and the TeV cutoff of the electron spectrum

– If confirmed, the fine structure may be telling us something – What’s beyond ~1 TeV?

Dark matter vs Astrophysical source– Distribution and spectrum of the diffuse γ-ray emission at HE (Fermi)

To answer these important questions we should consider all relevant astrophysical data (CRs, gamma rays) and particle data (LHC) together


Thank you !

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leptons in cosmic rays:

Documents

baldini head

heliosphere head

calibration issues head

propagation of cosmic

production galprop head

correct explanation

pamela positron fraction

leptonspecific issues