Tsunefumi Mizuno 1 Fermi_CR_2009Sep_GRBsymposium.ppt Galactic Cosmic- Rays Observed by Fermi-LAT (and GRBs) Tsunefumi Mizuno Hiroshima Univ. on behalf

Tsunefumi Mizuno 1

Fermi_CR_2009Sep_GRBsymposium.ppt

Galactic Cosmic-Galactic Cosmic-Rays Observed by Rays Observed by

Fermi-LAT (and Fermi-LAT (and GRBs)GRBs)

Tsunefumi MizunoTsunefumi MizunoHiroshima Univ.Hiroshima Univ.

on behalf of the Fermi-LAT on behalf of the Fermi-LAT CollaborationCollaboration

GRB Symposium “Deciphering the GRB Symposium “Deciphering the Ancient Universe”Ancient Universe”

September 26, 2009, Gifu, JapanSeptember 26, 2009, Gifu, Japan

Tsunefumi Mizuno 2


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 -ray

emission observed by Fermi-LAT (CRs in

distant location)

Tsunefumi Mizuno 3


Introduction:Introduction:Cosmic-Rays and the Cosmic-Rays and the

Fermi Gamma-ray Space TelescopeFermi Gamma-ray Space Telescope

Tsunefumi Mizuno 4


Cosmic-Rays Overview

V. Hess, 1912

Energy (eV)

Flu

x (m

2 s

r s

GeV

)-1

1 particle/m2/sec

Knee

1 particle /m2/yr

Ankle

1 particle/km2/yr

• Discovered by V. Hess in 1912• Globally power-law spectrum with some structures (knee and ankle)

hint of the origin E<Eknee are (probably) Galactic origin

Galactic

Extragalactic

G or EG?

• Composition: e- ~ (1/100 - 1/1000) x p, e+ ~ (1/10) x e-

• Large energy density: ~1 eV cm-3

comparable to UB and Urad

• Studied by direct and indirect measurements• GRBs are the possible origin of ultra high-energy CRs. May also affect the Galactic CRs. (e.g., Wick et al. 2004)

直接観測・間接両方の手段

• GRB は、最高エネルギー宇宙線、 knee 付近の銀河宇宙線の起源として有力• 宇宙線研究：起源と伝播・分布

Tsunefumi Mizuno 5

Fermi_CR_2009Sep_GRBsymposium.pptIntroduction (1):Introduction (1):What Can We Learn from HE eWhat Can We Learn from HE e--/e/e++ (and p/p) ? (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 sources

• 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) sources

• Different measurements provide complementary information of the origin, acceleration and propagation of cosmic rays

All available data must be interpreted in a coherent scenario

Study nearby sources (astrophysical or exotic)e- + e+ : 近傍の宇宙線源を探るプローブ

Tsunefumi Mizuno 6

Fermi_CR_2009Sep_GRBsymposium.pptIntroduction (2): Introduction (2): What Can We Learn from Galactic Diffuse Gamma-Rays?What Can We Learn from Galactic Diffuse Gamma-Rays?

e+-

X,γISM

diffusiondiffusion energy losses energy losses reaccelerationreacceleration convectionconvection etc.etc.

π0

synchrotron

bremssHESS

SNR SNR RX J1713-3946RX J1713-3946

B

Pulsar,-QSO

PPHeHeCNOCNO

Chandra, Suzaku, Radio telescopes

A powerful probe to study CRs (mostly protons) in distant locations

HE -rays are produced via interactions between Galactic cosmic-rays (CRs) and the interstellar medium (or interstellar radiation field)

IC

ACTs, Fermi

gas

gas

ISRF

e+-

π+-

(CR Accelerator) (Interstellar space) (Observer)

diffuse : 宇宙線分布を探るプローブ

Tsunefumi Mizuno 7


LAT

GBM

TwoTwo instruments: instruments: • Large Area Telescope (LAT)Large Area Telescope (LAT)

20 MeV - >300 GeV20 MeV - >300 GeV

• Gamma-ray Burst Monitor (GBM)Gamma-ray Burst Monitor (GBM)

8 keV - 40 MeV8 keV - 40 MeV

Ideal for the direct and indirect (through -ray obs.) measurement of CRs

Fermi Gamma-ray Space TelescopeFermi Gamma-ray Space Telescope

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 -rays

• Calorimeter: hodoscopic CsI scintillators ~8.5 R.L. (vertical) Energy measurement Also serves as an Imaging Calorimeter

直接測定 (e- + e+) 、間接測定 (diffuse )

Tsunefumi Mizuno 8


Fermi-LAT Results (1):Fermi-LAT Results (1):CR ElectronsCR Electrons

-- Nearby CR Sources? ---- Nearby CR Sources? --

Tsunefumi Mizuno 9

Fermi_CR_2009Sep_GRBsymposium.pptQuick Review ofQuick Review of

Positron and Antiproton Fraction: 2008-09Positron and Antiproton Fraction: 2008-09

• 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)

PAMELA positron and antiprotonNature 458, 607 (2009)PRL 102, 051101 (2009)

1 GeV 10 100

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 10


FOM for CRE MeasurementFOM for CRE Measurement

Exposure factor (effectively) determines the # of countsEf(E) = Gf(E)*Tobs

L. Baldini

• The exposure factor determines the statistics• Imaging calorimeters (vs. spectrometers) feature larger Gf• Space (vs. balloon) experiments feature longer Tobs

(m2 sr)

Fermi-LAT gives the largest Ef and highest statistucs

Fermi-LAT: 最大の統計を誇る

Tsunefumi Mizuno 11


Fermi-LAT Capability for CR Electrons

Geometric Factor (Gf)

Residual hadron contamination

20 GeV 100 GeV 1 TeV

Energy Resolution BG rejection (E>150 GeV)

• Validate the MC against the beam test up to 280 GeV

• Finite energy resolution is taken into account in the spectrum.

• compare the flight histogram with the simulated ones, and account for the differences in systematic errors

Beam test で MC を verify

Tsunefumi Mizuno 12


Fermi-LAT Electron Spectrum• Abdo et al. Phys. Rev. Let. 102, 181101 (2009)

• 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: 0=2.54 diffusion coefficient index: =0.33 • no ATIC excess

• hard spectrum ( ~ 3)

Tsunefumi Mizuno 13


Implication from Fermi-LAT CRE (1)

re-Fermi “conventional” CRE Model

New “conventional” CRE models

0=2.54

0=2.42 0=2.33

• 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.

• for detail, see D. Grasso et al. 2009 (Astroparticle Physics, 32, 140)

• New “conventional” model0=2.42 (=0.33, w/ reacceleration)0=2.33 (=0.6, plain diffusion)

パラメタをちょっといじれば OK

Tsunefumi Mizuno 14


Implication from Fermi-LAT CRE (2)

New “conventional” CRE models

Old “conventional” CRE Model

• Now include recent PAMELA result on positron fraction

• If the secondary positrons only e+/(e- + e+) ~ E^(-P+0); P~2.7 (proton spectral index), 0~2.4 The hard e+ + e- spectrum found by Fermi-LAT sharpens the anomaly

2ndary 起源なら必ず右下がりになる=>positron excess はこの反対

Tsunefumi Mizuno 15


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.

Unavoidable e+e- production by CRs and the ISM

And those that create positron excess at high energies.

Nearby (d<1 kpc) and Mature (104 - 106 yr) pulsars (e.g., Grasso+ 09)

Nearby GRB (or GRB-like event) (Ioka 09)

Nearby SNR in dense cloud (e.g., Fujita+ 09)

Dark matter (many including Grasso+ 09)

Klein-Nishina effect (Stawarz+ 09, Schlickeiser+ 09)

“conventional” sources

• Fermi data requires an e-/e+ injection spectrum significantly harder than generally expected for shell-type SNRs

宇宙線源を直接とらえた？Pulsar, GRB, etc..

Tsunefumi Mizuno 16


Pulsar Scenario

• An example of the fit to both Fermi and PAMELA data with Monogem and Geminga with a nominal choice for the e+/e- injection parameter (blue lines).

(Discrepancy in positron fraction at low energies can be understood as the charge-sign effect of solar modulation)

This particular model assumes:40% e-/e+ conversion efficiency =1.7Ecut=1 TeVDelay=60 kyr

(Emax=1/bt, b=1.4x10-16 GeV-1 s-1)

適当なパラメタで Fermi/PAMELA とも説明可能

Tsunefumi Mizuno 17


GRB Scenario?GRB Scenario?

• model (a) fits to the Fermi and PAMELA data well:tage = 2x105 yrEe+ = 0.9 x 1050 erg = 2.5, up to 10TeVb = 10-16 GeV-1 s-1

• ATIC data can also be explained by a somewhat harder and older GRB-like event• Chance probability of having such a GRB: ~0.6-6 %

Ioka 2009 (arXiv: 0812.4851)

近場の GRB でも (Pulsarと同様に )OK

Tsunefumi Mizuno 18


Summary of CRESummary of CRE

• Real breakthrough during last 1-1.5 years in CR electrons: ATIC, HESS,

PAMELA and finally Fermi-LAT• The hard e-/e+ spectrum by Fermi contradicts with PAMELA’s positron

fraction.• We may be coming close to the first detection of cosmic-ray sources• Source nature (astrophysical or exotic) is still unclear but strongly

constrained by the data of Fermi-LAT (+ others)• More results from Fermi-LAT are coming. Extending energy range to 5 GeV –

2 TeV and searching for the CRE anisotropy at a level of ~1%.

Ioka 09

近場の宇宙線源をとらえた？異方性がでれば決め手になりうる

Tsunefumi Mizuno 19


Fermi-LAT Result (2): Fermi-LAT Result (2): Diffuse Gamma-ray Emission and Diffuse Gamma-ray Emission and

Galactic CRsGalactic CRs

Tsunefumi Mizuno 20


Probing CRs using Gamma-raysProbing CRs using Gamma-rays

• HE s are generated through pi0-decay (p and ISM), bremsstrahlung (e+e- and ISM) and IC (e+e- and IRF)• CR spectrum can be deduced from the gamma-ray data and the ISM distribution

ISM(e.g., LAB HI survey)

(http://www.astro.uni-bonn.de/~webaiub/english/tools_labsurvey.php)

Gamma-ray intensity(Fermi LAT data)

Mid/high latitude region & Galactic plane:Study of the local CRs and CR gradient in the outer Galaxy

GCsun

(From Wikipedia)

線 = ISM * 宇宙線

Tsunefumi Mizuno 21


Outstanding Question: EGRET GeV ExcessOutstanding Question: EGRET GeV Excess

|b|=10°-20°

0.1 1 10 GeV

EGRETLAT

• EGRET showed excess emission > 1 GeV everywhere in the sky over the model based on directly measured CRs• a variety of explanations including large CR variation and DM annihilation

• |b|=10°-20°: avoid Gal. plane but still have high statistics• LAT spectrum is significantly softer and does not confirm the EGRET GeV excess

Preliminary

PreliminaryAbdo et al. submitted to PRLPorter et al. 2009 (arXiv:0907.0294)

GeV excess は確認されず

~2.7 の PL で落ちてくれない )

Tsunefumi Mizuno 22


Accurate Measurements of the Local CRsAccurate Measurements of the Local CRs

Mid-high lat. region in 3rd quadrant:• small contamination of IC and molecular gas• correlate -ray intensity and HI gas column density

Abdo et al. 2009 (contact: TM)

electron-bremsstrahlung

nucleon-nucleon

LAT datamodel for the LIS

• Best quality -ray emissivity spectrum (per H-atom) in 100 MeV-10 GeV (Tp = 1-100 GeV)

• Directly measured CR spectrum (LIS) is representative of the local CR spectrum

• Not easy to detect the additional e-/e+ signal through s. (no hadron rejection)

近傍の宇宙陽子線は LIS に酷似

Tsunefumi Mizuno 23


CR Distribution in GalaxyCR Distribution in Galaxy• CR distribution is a key to understand

their origin and propagation• Distribution of SNRs not well measured• Previous Gamma-ray data suggests a

flatter distribution than SNR/pulsar

distributions (e.g., Strong et al. 2004)

Gal.Center

Inner Galaxy

OuterGalaxy

• Fermi-LAT is able to map out CR distributions in the Galaxy with unprecedented accuracy• Large scale analysis in progress. (arXiv:0907.0304, arXiv:0907.0312)

• Preliminary analysis of the 3rd quadrant (outer Galaxy) will be discussed.

CR source distribution from -rays(Strong & Mattox 1996)

SNR distribution

(Case & Bhattacharya 1998)

0 5 10 15 kpc

Pulsar distribution(Lorimer 2004)

sun

銀河面拡散線 : 宇宙線の空間分布

local arm

Perseus arm

Tsunefumi Mizuno 24


Fermi-LAT View of the 3rd QuadrantFermi-LAT View of the 3rd Quadrant• One of the best studied regions in -rays

Vela, Geminga, Crab and Orion A/B• Galactic plane between Vela and Geminga (green square) is ideal to study diffuse -rays and CRs.

small point source contamination, kinematically well-separated arms (local arm and Perseus arm)

Count Map (E>100 MeV)

Preliminary

Preliminary

Vela

Crab

Geminga

Orion A/B

Tsunefumi Mizuno 25


Construction of the ModelConstruction of the Model

Local arm

+

Local arm

+ others (ISM, IC and point sources)

• Fit gamma-ray data with a linear combination of model maps

I(E, l, b) = A(E)*HI(l,b) + B(E)*Wco(l,b) +others+point_sources

• Coefficients give the gamma-ray (CR) spectral distribution of outer Galaxy

Preliminary

Preliminary

Perseus arm

+

=

拡散線 = ISM* 宇宙線+

Tsunefumi Mizuno 26


HI Emissivity (CR) SpectraHI Emissivity (CR) Spectra

Preliminary

Preliminary

HI Emissivity Spectrum of each ring

Point sources with Ts>=100 are included in the fitting

(local arm)(interarm)(Perseus arm)

• Emissivity spectrum of local arm (R=8.5-10 kpc) is slightly smaller than the model for LIS• Decreasing emissivity (local arm => interarm => Perseus arm) are interpreted to be du to the decreasing CR density across the Galaxy• Similar CR spectral shape up to R=16 kpc • Can constrain the CR source distribution and propagation parameters

study in progress 銀河宇宙線の分布が明らかになりつつある

Tsunefumi Mizuno 27


SummarySummary

• Fermi-LAT is a powerful instrument to measure CRs either directly or indirectly

• Fermi-LAT revealed that high-energy e- + e+ spectrum is harder than previously assumed.

this finding + PAMELA positron fraction require local sources (astrophysical or exotic) nearby GRB is one of possible origins Source nature is still unclear but strongly constrained.

• CRs in distant locations can be “measured” by diffuse -rays. EGRET GeV-excess not confirmed. Fermi proves that local CR nuclei spectra are close to those of LIS. CR density distribution in outer Galaxy is being studied.

Thank you for your attention!

宇宙線電子：近傍の宇宙線源をとらえた？

拡散線：銀河宇宙線の大局分布が明らかになりつつある

Documents

Tsunefumi Mizuno 1 Fermi_CR_2009Sep_GRBsymposium.ppt Galactic Cosmic- Rays Observed by Fermi-LAT (and GRBs) Tsunefumi Mizuno Hiroshima Univ. on behalf