Fermi_CR_2009Sep_GRBsymposium.ppt Galactic Cosmic Galactic Cosmic- - Rays Observed by Rays Observed by Rays Observed by Rays Observed by Fermi- Fermi -LAT (and LAT (and GRBs) GRBs) GRBs) GRBs) Tsunefumi Tsunefumi Mizuno Mizuno Hiroshima Univ. Hiroshima Univ. on behalf of the Fermi on behalf of the Fermi- -LAT LAT Collaboration Collaboration Collaboration Collaboration GRB Symposium “Deciphering the GRB Symposium “Deciphering the Ancient Universe” Ancient Universe” Ancient Universe Ancient Universe September 26, 2009, Gifu, Japan September 26, 2009, Gifu, Japan Tsunefumi Mizuno 1
Fermi_CR_2009Sep_GRBsymposium.ppt Plan of the Talk Plan of the Talk 1. Cosmic-ray overview and Fermi Gamma- ray Space Telescope 2. Cosmic-ray electrons seen by Fermi-LAT (nearby CR sources) 3. Galactic CRs revealed by diffuse γ -ray Galactic CRs revealed by diffuse γ -ray 3 emission observed by Fermi-LAT (CRs in distant location) ) Tsunefumi Mizuno 2
Fermi_CR_2009Sep_GRBsymposium.ppt Introduction: Introduction: Introduction: Introduction: Cosmic Cosmic- -Rays and the Rays and the Fermi Gamma Fermi Gamma ray Space Telescope Fermi Gamma Fermi Gamma-ray Space Telescope ray Space Telescope ray Space Telescope Tsunefumi Mizuno 3
Fermi_CR_2009Sep_GRBsymposium.ppt Cosmic-Rays Overview • Discovered by V. Hess in 1912 V. Hess, 1912 • Globally power-law spectrum with some structures (knee and ankle) and ankle) � hint of the origin � E<E knee are (probably) Galactic origin • Composition: • Composition: 1 particle/m 2 /sec � e - ~ (1/100 - 1/1000) x p, e + ~ (1/10) x e - • Large energy density: ~1 eV cm -3 eV) - 1 Galactic � comparable to U and U � comparable to U B and U rad x (m 2 sr s Ge • Studied by direct and indirect G or EG? measurements 直接観測・間接両方の手段 Knee 1 particle /m 2 /yr 1 particle /m 2 /yr • GRBs are the possible origin of GRB h ibl i i f Flu Extragalactic ultra high-energy CRs. May also Ankle affect the Galactic CRs. (e.g., Wick et ( g , 1 particle/km 2 /yr 1 particle/km 2 /yr • GRB は、最高エネルギー宇宙線、 knee al. 2004) 付近の銀河宇宙線の起源として有力 Energy (eV) • 宇宙線研究：起源と伝播・分布 Tsunefumi Mizuno 4
Fermi_CR_2009Sep_GRBsymposium.ppt Introduction (1): Introduction (1): /e + (and p/p) ? What Can We Learn from HE e - /e What Can We Learn from HE e (and p/p) ? • Inclusive spectra: e - + e + � Electrons, unlike protons, lose energy rapidly by Synchrotron and Inverse Compton: at very high energy they probe the nearby d I C t t hi h th b th b sources • Charge composition: e + /(e - + e + ) and p/(p + p) ratios • Charge composition: e + /(e + e + ) and p/(p + p) ratios � e + and p are produced by the interactions of high-energy cosmic rays with the interstellar matter (secondary production) � There might be signals from additional (astrophysical or exotic) � There might be signals from additional (astrophysical or exotic) sources • Different measurements provide complementary information of the p p y origin, acceleration and propagation of cosmic rays � All available data must be interpreted in a coherent scenario e - + e + : 近傍の宇宙線源を探るプロ e - + e + : 近傍の宇宙線源を探るプローブ ブ Study nearby sources (astrophysical or exotic) Tsunefumi Mizuno 5
Fermi_CR_2009Sep_GRBsymposium.ppt Introduction (2): Introduction (2): What Can We Learn from Galactic Diffuse Gamma What Can We Learn from Galactic Diffuse Gamma- -Rays? Rays? HE γ -rays are produced via interactions between Galactic cosmic-rays (CRs) and the interstellar medium (or interstellar radiation field) (CR Accelerator) (Interstellar space) (Observer) (CR Accelerator) (Interstellar space) (Observer) ISM SNR SNR X, γ RX J1713 RX J1713- -3946 3946 + - Chandra Suzaku Chandra, Suzaku, e Radio telescopes B IC HESS ISRF P diffusion diffusion diffusion diffusion He He energy losses energy losses CNO CNO gas reacceleration reacceleration Pulsar, π 0 - + e μ -QSO convection convection + - π π etc etc etc. etc. ACTs , Fermi Fermi ACT gas diffuse γ : 宇宙線分布を探るプローブ γ A powerful probe to study CRs (mostly protons) in distant locations Tsunefumi Mizuno 6
Fermi_CR_2009Sep_GRBsymposium.ppt Fermi Gamma Fermi Gamma- -ray Space Telescope ray Space Telescope LAT Two Two instruments: instruments: • Large Area Telescope (LAT) Large Area Telescope (LAT) 20 20 MeV MeV - - >300 >300 GeV GeV • Gamma Gamma- -ray Burst Monitor (GBM) ray Burst Monitor (GBM) 8 keV 8 keV - - 40 40 MeV MeV GBM GBM Fermi-LAT consists of three subsystems • ACD: segmented plastic scintillators � BG rejection • Tracker: Si-strip detectors & W converters � ~1.5 R.L. (vertical) � Identification and direction measurement of γ -rays • Calorimeter: hodoscopic CsI scintillators • Calorimeter: hodoscopic CsI scintillators � ~8.5 R.L. (vertical) � Energy measurement � Also serves as an Imaging Calorimeter Ideal for the direct and indirect (through γ -ray obs.) 直接測定 (e - + e + ) 、間接測定 (diffuse γ ) measurement of CRs Tsunefumi Mizuno 7
Fermi_CR_2009Sep_GRBsymposium.ppt Fermi Fermi-LAT Results (1): Fermi Fermi LAT Results (1): LAT Results (1): LAT Results (1): CR Electrons CR Electrons -- -- Nearby CR Sources? Nearby CR Sources? Nearby CR Sources? Nearby CR Sources? -- -- Tsunefumi Mizuno 8
Fermi_CR_2009Sep_GRBsymposium.ppt Quick Review of Quick Review of Positron and Antiproton Fraction: 2008 Positron and Antiproton Fraction: 2008- -09 09 PAMELA positron and antiproton Nature 458, 607 (2009) PRL 102, 051101 (2009) PRL 102, 051101 (2009) 1 GeV 10 100 • Antiproton fraction consistent with secondary production • Anomalous rise in the positron fraction above 10 GeV • Several different viable interpretations (>200 papers over the last year) See also Nature 456, 362 (2008) and PRL 101, 261104 (2008) for pre-Fermi CRE spectrum by ATIC and HESS. e + fraction excess は 2ndary 起源とは相いれない Tsunefumi Mizuno 9
Fermi_CR_2009Sep_GRBsymposium.ppt FOM for CRE Measurement FOM for CRE Measurement Exposure factor (effectively) determines the # of counts E f (E) = G f (E)*T obs Fermi-LAT: 最大の統計を誇る L. Baldini a d (m 2 sr) • The exposure factor determines the statistics • Imaging calorimeters (vs. spectrometers) feature larger Gf • Space (vs. balloon) experiments feature longer T obs Fermi-LAT gives the largest Ef and highest statistucs Tsunefumi Mizuno 10
Fermi_CR_2009Sep_GRBsymposium.ppt Fermi-LAT Capability for CR Electrons BG rejection (E>150 GeV) Energy Resolution • Validate the MC against the beam V lid t th MC i t th b test up to 280 GeV Geometric Factor (G f ) • Finite energy resolution is taken gy into account in the spectrum. • compare the flight histogram with Residual hadron the simulated ones and account for the simulated ones, and account for contamination contamination the differences in systematic errors 20 GeV 100 GeV 1 TeV Beam test で MC を verify Tsunefumi Mizuno 11
Fermi_CR_2009Sep_GRBsymposium.ppt Fermi-LAT Electron Spectrum • Abdo et al. Phys. Rev. Let. 102, 181101 (2009) • statistics for 6 month data • statistics for 6 month data � >4 million electrons above 20 GeV � >400 electrons in the last energy bin � Harder spectrum (spectral index: -3.04) than previously thought • Pre-Fermi reference model (GALPROP conventional model): ---------- � conventional source distribution (uniformly distributed distant sources) � source PL index: γ =2 54 � source PL index: γ 0 =2.54 � diffusion coefficient index: δ =0.33 • no ATIC excess • hard spectrum ( Γ ~ 3) Tsunefumi Mizuno 12
Fermi_CR_2009Sep_GRBsymposium.ppt Implication from Fermi-LAT CRE (1) • for detail, see D. Grasso et al. re-Fermi “conventional” CRE Model γ 0 =2.54 2009 (Astroparticle Physics, 32, 140) • New “conventional” model � γ 0 =2.42 ( δ =0.33, w/ reacceleration) reacceleration) New “conventional” CRE models � γ 0 =2.33 ( δ =0.6, plain γ 0 =2.42 γ 0 =2.33 diffusion) • Fermi CRE spectrum can be reproduced by the “conventional” model with harder injection spectral index (-2.42) than in a pre-Fermi conventional model (-2.54), within our current uncertainties both statistical and systematic. パラメタをちょっといじれば OK Tsunefumi Mizuno 13
Fermi_CR_2009Sep_GRBsymposium.ppt Implication from Fermi-LAT CRE (2) • Now include recent PAMELA result on positron fraction 2ndary 起源なら必ず右下がりになる =>positron excess はこの反対 はこの反対 it New “conventional” CRE models Old “conventional” CRE Model • If the secondary positrons only � e + /(e - + e + ) ~ E^(- γ P + γ 0 ); γ P ~2.7 (proton spectral index), γ 0 ~2.4 P 0 P 0 � The hard e + + e - spectrum found by Fermi-LAT sharpens the anomaly Tsunefumi Mizuno 14
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