Fermi_CR_2009Sep.ppt Galactic Cosmic Galactic Cosmic- - Rays Observed by Rays Observed by Rays Observed by Rays Observed by Fermi Fermi- -LAT LAT Tsunefumi Tsunefumi Mizuno Mizuno Hiroshima Univ. Hiroshima Univ. on behalf of the Fermi on behalf of the Fermi- -LAT LAT Collaboration Collaboration Collaboration Collaboration JPS 2009 Autumn Meeting JPS 2009 Autumn Meeting September 11, 2009, Kobe, Japan September 11, 2009, Kobe, Japan p p , , , , , , p p Tsunefumi Mizuno 1
Fermi_CR_2009Sep.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 (direct measurement of CRs) 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.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.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 B and U rad � comparable to U and U x (m 2 sr s Ge • Studied by direct and indirect G or EG? measurements Knee 1 particle /m 2 /yr 1 particle /m 2 /yr Flu Extragalactic Ankle 1 particle/km 2 /yr 1 particle/km 2 /yr Energy (eV) Tsunefumi Mizuno 4
Fermi_CR_2009Sep.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 Study nearby sources (astrophysical or exotic) Tsunefumi Mizuno 5
Fermi_CR_2009Sep.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 A powerful probe to study CRs in distant locations Tsunefumi Mizuno 6
Fermi_CR_2009Sep.ppt Fermi Launch Fermi Launch • Launched from Cape Canaveral Air Station on June 11, 2008 • Science Operation on Aug 4, 2009 Science Operation on Aug 4 2009 • Orbit: 565 km, 26.5 o (low BG) Tsunefumi Mizuno 7
Fermi_CR_2009Sep.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.) measurement of CRs Tsunefumi Mizuno 8
Fermi_CR_2009Sep.ppt Fermi Fermi-LAT Results (1): Fermi Fermi LAT Results (1): LAT Results (1): LAT Results (1): Direct Measurements of Galactic Direct Measurements of Galactic CR Electrons CR Electrons CR Electrons CR Electrons Tsunefumi Mizuno 9
Fermi_CR_2009Sep.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. Tsunefumi Mizuno 10
Fermi_CR_2009Sep.ppt Fermi-LAT Capability for CR Electrons • Candidate electrons pass through 12.5 X 0 on average ( Tracker and Calorimeter added together) • Simulated residual hadron contamination (5-21% increasing with the ( g energy) is deducted from resulting flux of electron candidates • Effective geometric factor (G f ) exceeds 2.5 [m 2 sr] for 30 GeV to 200 GeV, and decreases to ~1 [m 2 sr] at 1 TeV. G f times live time has already reached [ ] y f several x 10 7 [m 2 sr s]. (very high statistics) • Full power of all LAT subsystems is in use: Tracker, Calorimeter and ACD act together Geometric Factor (G f ) Residual hadron contamination 20 GeV 100 GeV 1 TeV Tsunefumi Mizuno 11
Fermi_CR_2009Sep.ppt FOM for CRE Measurement FOM for CRE Measurement Exposure factor (effectively) determines the # of counts E f (E) = G f (E)*T obs L B ldi i L. Baldini • The exposure factor determines the statistics • The exposure factor determines the statistics • Imaging calorimeters (vs. spectrometers) feature larger Gf • Space (vs. balloon) experiments feature longer T obs Tsunefumi Mizuno 12
Fermi_CR_2009Sep.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 Tsunefumi Mizuno 13
Fermi_CR_2009Sep.ppt Implication from Fermi-LAT CRE (1) • for detail, see D. Grasso et al. re-Fermi “conventional” CRE Model γ 0 =2.54 arXiv:0905.0636 (accepted by Astroparticle Physics) p y ) • 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. Tsunefumi Mizuno 14
Fermi_CR_2009Sep.ppt Implication from Fermi-LAT CRE (2) • Now include recent PAMELA result on positron fraction 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) P 0 P � The hard e + + e - spectrum found by Fermi-LAT sharpens the anomaly Tsunefumi Mizuno 15
Fermi_CR_2009Sep.ppt Implication from Fermi-LAT CRE (3) • It is becoming clear that we are dealing with at least 3 distinct origins of HE e - /e + � Uniformly distributed distant sources, likely SNRs. “conventional” sources � Unavoidable e + e - production by CRs and the ISM � And those that create positron excess at high energies. Nearby (d<1 kpc) and Mature (10 4 - 10 6 yr) pulsars? DM? • Energy source: rotation energy of the NS • Electron and positrons are re-accelerated at the pulsar wind/shock with a power law spectrum with index Γ 1.5 wind/shock with a power law spectrum with index Γ ~1.5 • e - /e + are expected to be confined until T~10-100 kyr after the birth of pulsar. Only mature (10<T<1000 kyr) pulsars are expected to be relevant pulsars are expected to be relevant • E cut ~10 3 TeV for young PWN. It is expected to decrease with the pulsar age (E cut ~0.1-10 TeV for mature pulsars) • Fermi data requires an e-/e+ injection spectrum significantly harder than generally expected for shell-type SNRs Tsunefumi Mizuno 16
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