Moskalenko stanfordkipac Leptons in Cosmic Rays 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 ID: 547698
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Slide1
Igor V.
Moskalenko
(stanford/kipac)
Leptons in Cosmic Rays:Slide2
Positron fractionThe 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)Slide3
Cosmic ray electronsA slope the CR electron spectrum can be easily reproduced in propagation modelsMost interesting is the fine structure, if confirmed, and the cutoff at ~1 TeV
Latronico+’09
What’s here?Slide4
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+ citationsOf course, most of citations are coming from particle physics★ using NASA ADSSlide5
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)PulsarsSNRsMicroquasarsa 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 explanationSlide6
The Goal of This TalkTo discuss a place of recent leptonic data in astrophysics of cosmic rays
Some
c
alibration issues
A couple of words about
heliospheric
modulation
How well do we understand the propagation of CRs?Lepton-specific issuesSlide7
Calibration IssuesSlide8
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.Slide9
CR measurements and backgroundsCR protons are the dominant background for positron detectionPAMELA people made a tremendous job by hunting down every proton (see Mirko’s talk)
See Marty’s summary
L.BaldiniSlide10
Cosmic rays in the heliosphereSlide11
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 minSolar 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).Slide12
Probes of propagation in the interstellar medium
nuclei in cosmic rays diffuse Galactic γ-raysSlide13
Secondary/primary nuclei ratio & CR propagation
Using secondary/primary nuclei ratio
(B/C) & flux:
Diffusion coefficient and its indexPropagation mode and its parameters (e.g., reacceleration VA, convection
V
z)
Propagation
parameters are model-dependentMake sure that the spectrum is fitted as wellRadioactive isotopes:Galactic halo size ZhZh increaseBe10/Be9Ek,
MeV
/nucleon
Parameters (model dependent):
D~ 10
28
(
ρ
/1 GV)
α
cm2/s
α
≈
0.3-0.6
Z
h
~ 4-6
kpc
V
A
~ 30 km/
s
Boron/Carbon (B/C)
Interstellar
E
k
,
MeV
/nucleonSlide14
Radioactive secondaries
Different
size from different ratios…
Z
halo,kpc
ST
W
27
Al+p
26
Al
In determination of the propagation parameters one has to take into account:
Errors
in CR measurements
(@ HE
& LE)
Errors in production cross sections
Errors in the lifetime estimates
nat
Si+p
26
Al
W
ST
T
1/2
=
?
W – Webber+
ST
– Silberberg &
Tsao
- - -
– measured
The error bars can be significantly reduced if more accurate cross sections are used
Different ratios provide consistent parametersSlide15
Diffusion coefficient in different models
Plain
diffusion
Diffusive
Reacceleration
(
Kolmogorov
)Reaccelerationwith damping~R0.6~β-3extrapolationPtuskin+’06The diffusion coefficient is model-dependent and is derived from secondary/primary nuclei ratio below ~100 GV It is extrapolated above this energydataSlide16
PAMELA & CREAM: B/C ratioThe B/C ratio <30 GeV/n is measured by Pamela (no surprises)
Statistical errors only
Sparvoli’09PAMELA 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!Slide17
CR Protons & He The CR proton and He spectra by Pamela agree well with previous measurementsNo 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+’02Slide18
AntiprotonsAntiprotons in CRs
(BESS, Pamela) <100 GeV are in agreement with secondary production
PAMELAPicozza’09
Picozza’09|Ptuskin+’06Slide19
Fermi-LAT: diffuse gammasConventional 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+’09Slide20
Spectrum of the Galactic diffuse emission, longitude and latitude profilesCR 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 I
Total diffuse
Bright sourcesπ0-decayInverse ComptonBremsstrahlungIsotropic componentPRELIMINARYSlide21
Lepton-specific issuesSlide22
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 modelsMulti-component interpretation is also possibleDark matter contributionAstrophysical 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 Slide23
Geminga
pulsar
Milagro C3Pulsar (AGILE/Fermi)MGRO 2019+37Fermi PulsarSNR g
CygniFermi PulsarHESS, Milagro, Magic
Fermi Pulsar
Milagro
(C4)3EG 2227+6122
Boomerang PWNSNR IC433MAGIC, VERITASRadio pulsar (new TeV source)unID(new TeV source)unID(new TeV source)Fermi PulsarMGRO 1908+06HESS 1908+063SNR W51HESS J1923+141G65.1+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
)Slide24
Effective propagation distanceThe energy loss time scale (IC) at ~1 GeV – 1 TeV: τ
~ 300 E12-1 kyr ~ 10
13 E12-1 cm; E12 – energy in TeVThe diffusion coefficient: D ~ (0.5-1)x1030 E121/2 cm2/sEffective propagation distance: <X> ~ √6Dτ ~ 5x1021 E12
-1/4 cm ~ 1 kpc E12-1/4We 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.Slide25
Solar system in the Milky Way
The solar system is located in the inter-arm region – a very safe place!Slide26
(Some) Important questions to answerHow 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 positronsFine structure and the TeV cutoff of the electron spectrumIf confirmed, the fine structure may be telling us something What’s beyond ~1 TeV?Dark matter
vs Astrophysical sourceDistribution 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) togetherSlide27
Thank you !
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