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Leptons in Cosmic Rays:

Leptons in Cosmic Rays:. Igor V. Moskalenko ( stanford/kipac ). 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?

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Leptons in Cosmic Rays:

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  1. Leptons in Cosmic Rays: Igor V. Moskalenko (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 sec. production (GALPROP) Solar modulation Adriani+’08

  3. 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 What’s here? Latronico+’09

  4. 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

  5. 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

  6. The Goal of This Talk To 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

  7. Calibration Issues

  8. Fermi-LAT:the Earth’s albedo A 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.

  9. 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

  10. Cosmic rays in the heliosphere

  11. 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. 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). M.Potgieter

  12. Probes of propagation in the interstellar mediumnuclei in cosmic rays diffuse Galactic γ-rays

  13. Secondary/primary nuclei ratio & CR propagation Radioactive isotopes: Galactic halo size Zh Be10/Be9 Boron/Carbon (B/C) Interstellar Ek, MeV/nucleon Zh increase • 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 Ek, MeV/nucleon Parameters (model dependent): D~ 1028 (ρ/1 GV)α cm2/s α≈ 0.3-0.6 Zh ~ 4-6 kpc VA ~ 30 km/s

  14. natSi+p26Al ST W 27Al+p26Al W ST Radioactive secondaries 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 Different size from different ratios… T1/2=? W – Webber+ ST – Silberberg & Tsao - - - – measured Zhalo,kpc • The error bars can be significantly reduced if more accurate cross sections are used • Different ratios provide consistent parameters

  15. Diffusion coefficient in different models • The diffusion coefficient is model-dependent and is derived from secondary/primary nuclei ratio below ~100 GV • It is extrapolated above this energy ~R0.6 Reacceleration with damping Plain diffusion ~β-3 data extrapolation Diffusive Reacceleration (Kolmogorov) Ptuskin+’06

  16. PAMELA & CREAM: B/C ratio The B/C ratio <30 GeV/n is measured by Pamela (no surprises) PAMELA Very preliminary! • Launched on Dec. 1, 2009, CREAM-V just finished its 3rd circle around the South Pole! Statistical errors only • Sparvoli’09 CREAM Ahn+’08 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)

  17. 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 H: -2.752±0.071 He: -2.624±0.122 PAMELA Picozza’09 He protons IM+’02

  18. Antiprotons PAMELA Picozza’09 • Antiprotons in CRs (BESS, Pamela) <100 GeV are in agreement with secondary production |Ptuskin+’06 • Picozza’09

  19. 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

  20. 1.2 GeV ≤ E ≤ 1.6 GeV Spectrum of the Galactic diffuse emission, longitude and latitude profiles |b|≤5° CR intensities are adjusted by a factor: protons – 1.3, electrons - 1.5 |b|≤5,°|l|≤30° PRELIMINARY Total diffuse Bright sources π0-decay Inverse Compton Bremsstrahlung Isotropic component Loop I |l|≤60°

  21. Lepton-specific issues

  22. 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

  23. 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) unID (new TeV source) Fermi Pulsar MGRO 1908+06 HESS 1908+063 unID (new TeV source) Geminga pulsar Milagro C3 Radio pulsar (new TeV source) SNR IC433 MAGIC, VERITAS G.Sinnis’09 Pulsar (AGILE/Fermi) MGRO 2019+37 Fermi Pulsar SNR gCygni Fermi Pulsar HESS, Milagro, Magic Fermi Pulsar Milagro (C4) 3EG 2227+6122 Boomerang PWN G65.1+0.6 (SNR) Fermi Pulsar (J1958) New TeV sources SNR W51 HESS J1923+141

  24. Effective propagation distance • The energy loss time scale (IC) at ~1 GeV – 1 TeV: τ~ 300 E12-1kyr ~ 1013 E12-1 cm; E12 – energy in TeV • The diffusion coefficient: D ~ (0.5-1)x1030 E121/2 cm2/s • Effective propagation distance: <X> ~ √6Dτ ~ 5x1021 E12-1/4 cm ~ 1 kpcE12-1/4 • 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.

  25. Solar system in the Milky Way The solar system is located in the inter-arm region – a very safe place!

  26. (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

  27. Thank you ! You are here

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