Galactic Cosmic Galactic Cosmic- - Rays Observed by Rays Observed - - PowerPoint PPT Presentation

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.

• n behalf of the Fermi
• n behalf of the Fermi-
• LAT

LAT Collaboration Collaboration Collaboration Collaboration

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

Tsunefumi Mizuno 1

Ancient Universe Ancient Universe September 26, 2009, Gifu, Japan September 26, 2009, Gifu, Japan

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

• 3. Galactic CRs revealed by diffuse γ-ray

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 ray Space Telescope Fermi Gamma Fermi Gamma-ray Space Telescope ray Space Telescope

Tsunefumi Mizuno 3

Fermi_CR_2009Sep_GRBsymposium.ppt

Cosmic-Rays Overview

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

and ankle) and ankle)

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

• Composition:

eV)-1 1 particle/m2/sec

Galactic

• Composition:

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

• Large energy density: ~1 eV cm-3

comparable to U and U

x (m2 sr s Ge Knee 1 particle /m2/yr

G or EG?

comparable to UB and Urad

• Studied by direct and indirect

measurements GRB h ibl i i f

直接観測・間接両方の手段

Flu 1 particle /m2/yr Ankle 1 particle/km2/yr

Extragalactic

• GRBs are the possible origin of

ultra high-energy CRs. May also affect the Galactic CRs. (e.g., Wick et

Tsunefumi Mizuno 4

Energy (eV) 1 particle/km2/yr

( g ,

• al. 2004)
• 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

Fermi_CR_2009Sep_GRBsymposium.ppt

Introduction (1): Introduction (1):

What Can We Learn from HE e What 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 d I C t t hi h th b th b and Inverse Compton: at very high energy they probe the nearby 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

• rigin, 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 ブ

Tsunefumi Mizuno 5

Study nearby sources (astrophysical or exotic)

e- + e+ : 近傍の宇宙線源を探るプローブ

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) X,γ ISM SNR SNR RX J1713 RX J1713-

• 3946

3946

Chandra Suzaku

(CR Accelerator) (Interstellar space) (Observer) e

+

• diffusion

diffusion HESS

B

P

Chandra, Suzaku, Radio telescopes

IC

ISRF

diffusion diffusion energy losses energy losses reacceleration reacceleration convection convection etc etc

π0 Pulsar, μ-QSO

He He CNO CNO ACT

Fermi

gas e

+

• π

+

• etc.

etc. ACTs, Fermi

gas π diffuse γ : 宇宙線分布を探るプローブ

Tsunefumi Mizuno 6

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

γ

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 GBM

• Gamma

Gamma-

• ray Burst Monitor (GBM)

ray Burst Monitor (GBM) 8 8 keV keV -

• 40

40 MeV MeV 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

Tsunefumi Mizuno 7

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

直接測定(e- + e+)、間接測定(diffuse γ)

Fermi_CR_2009Sep_GRBsymposium.ppt

Fermi Fermi-LAT Results (1): LAT Results (1): Fermi Fermi 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)

Tsunefumi Mizuno 9

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

Fermi_CR_2009Sep_GRBsymposium.ppt

FOM for CRE Measurement FOM for CRE Measurement

Exposure factor (effectively) determines the # of counts

Ef(E) = Gf(E)*Tobs

Fermi-LAT: 最大の統計を誇る

• L. Baldini

a d

• The exposure factor determines the statistics

(m2 sr)

Tsunefumi Mizuno 10

• Imaging calorimeters (vs. spectrometers) feature larger Gf
• Space (vs. balloon) experiments feature longer Tobs

Fermi-LAT gives the largest Ef and highest statistucs

Fermi_CR_2009Sep_GRBsymposium.ppt

Fermi-LAT Capability for CR Electrons

Energy Resolution BG rejection (E>150 GeV) V lid t th MC i t th b

Geometric Factor (Gf)

• Validate the MC against the beam

test up to 280 GeV

• Finite energy resolution is taken

Residual hadron contamination

gy into account in the spectrum.

• compare the flight histogram with

the simulated ones and account for

Tsunefumi Mizuno 11

contamination

20 GeV 100 GeV 1 TeV

the simulated ones, and account for the differences in systematic errors Beam testでMCをverify

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

Tsunefumi Mizuno 12

source PL index: γ0=2.54 diffusion coefficient index: δ=0.33

• no ATIC excess
• hard spectrum (Γ ~ 3)

Fermi_CR_2009Sep_GRBsymposium.ppt

Implication from Fermi-LAT CRE (1)

re-Fermi “conventional” CRE Model

γ0=2.54

• for detail, see D. Grasso et al.

2009 (Astroparticle Physics, 32, 140)

• New “conventional” model

γ0=2.42 (δ=0.33, w/ reacceleration)

New “conventional” CRE models

γ0=2.42 γ0=2.33 reacceleration) γ0=2.33 (δ=0.6, plain 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

Tsunefumi Mizuno 13

statistical and systematic.

パラメタをちょっといじればOK

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 it はこの反対 =>positron excessはこの反対

New “conventional” CRE models Old “conventional” CRE Model

• If the secondary positrons only

e+/(e- + e+) ~ E^(-γP+γ0); γP~2.7 (proton spectral index), γ0~2.4

Tsunefumi Mizuno 14

P P

The hard e+ + e- spectrum found by Fermi-LAT sharpens the anomaly

Fermi_CR_2009Sep_GRBsymposium.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. Unavoidable e+e- production by CRs and the ISM

“conventional” sources

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)

• Fermi data requires an e-/e+ injection spectrum

significantly harder than generally expected for h ll t SNR shell-type SNRs 宇宙線源を直接とらえた？ Pulsar GRB etc

Tsunefumi Mizuno 15

Pulsar, GRB, etc..

Fermi_CR_2009Sep_GRBsymposium.ppt

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). This particular model assumes: (E =1/bt b=1 4x10-16 GeV-1 s-1) This particular model assumes:

40% e-/e+ conversion efficiency Γ=1.7 Ecut=1 TeV Delay=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 16

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

Delay 60 kyr

Fermi_CR_2009Sep_GRBsymposium.ppt

GRB Scenario? GRB Scenario?

Ioka 2009 (arXiv: 0812.4851)

• model (a) fits to the Fermi and PAMELA data well:

t = 2x105 yr tage = 2x105 yr Ee+ = 0.9 x 1050 erg α = 2.5, up to 10TeV b = 10-16 GeV-1 s-1 近場のGRBでも(Pulsarと同 様に)OK

Tsunefumi Mizuno 17

• 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 %

Fermi_CR_2009Sep_GRBsymposium.ppt

Summary of CRE Summary 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%.

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

Ioka 09

異方性がでれば決め手になりうる

Tsunefumi Mizuno 18

Fermi_CR_2009Sep_GRBsymposium.ppt

Fermi Fermi-

• LAT Result (2):

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

Tsunefumi Mizuno 19

Fermi_CR_2009Sep_GRBsymposium.ppt

Probing CRs using Gamma Probing CRs using Gamma-

• rays

rays

• HE γs 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

di t ib ti

線 ISM * 宇宙線

distribution

ISM

(e.g., LAB HI survey)

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

Gamma-ray intensity

(Fermi LAT data)

γ線 = ISM * 宇宙線 Mid/high latitude region & Galactic plane: Study of the local CRs and CR gradient in the outer Galaxy

Tsunefumi Mizuno 20

GC sun (From Wikipedia)

Fermi_CR_2009Sep_GRBsymposium.ppt

Outstanding Question: EGRET Outstanding Question: EGRET GeV GeV Excess Excess

|b|=10°-20°

EGRET LAT 0 1 1 10 GeV

Abdo et al. submitted to PRL Porter et al 2009 (arXiv:0907 0294)

0.1 1 10 GeV

• EGRET showed excess emission > 1 GeV everywhere in the sky over

the model based on directly measured CRs i t f l ti i l di l CR i ti d DM

Porter et al. 2009 (arXiv:0907.0294)

(Γ~2.7のPLで落ちてくれない)

• a variety of explanations including large CR variation and DM

annihilation

• |b|=10° 20°: avoid Gal plane but still have high statistics

Tsunefumi Mizuno 21

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

GeV excess

GeV excessは確認されず

Fermi_CR_2009Sep_GRBsymposium.ppt

Accurate Measurements of the Local CRs Accurate Measurements of the Local CRs

Mid-high lat. region in 3rd quadrant:

• small contamination of IC and

molecular gas g

• correlate γ-ray intensity and HI

gas column density

Abdo et al. 2009 (contact: TM)

• Best quality γ-ray emissivity

spectrum (per H-atom) in 100 MeV-

LAT data model for the LIS

p (p ) 10 GeV (Tp = 1-100 GeV)

• Directly measured CR spectrum

(LIS) is representative of the local electron- nucleon-nucleon (LIS) is representative of the local CR spectrum

• Not easy to detect the additional

Tsunefumi Mizuno 22

bremsstrahlung e-/e+ signal through γs. (no hadron rejection) 近傍の宇宙陽子線はLISに酷似

Fermi_CR_2009Sep_GRBsymposium.ppt

CR Distribution in Galaxy CR Distribution in Galaxy

• CR distribution is a key to understand

their origin and propagation

• Distribution of SNRs not well measured

SNR distribution (C & Bh tt h 1998) Pulsar distribution (Lorimer 2004)

• Previous Gamma-ray data suggests a

flatter distribution than SNR/pulsar distributions (e.g., Strong et al. 2004)

CR source distribution from γ-rays (Strong & Mattox 1996) (Case & Bhattacharya 1998)

( g g )

• Fermi-LAT is able to map out CR

0 5 10 15 kpc

sun Gal. Center

• Fermi-LAT is able to map out CR

distributions in the Galaxy with unprecedented accuracy

• Large scale analysis in progress.

Inner Galaxy (arXiv:0907.0304, arXiv:0907.0312)

• Preliminary analysis of the 3rd

quadrant (outer Galaxy) will be

local arm

Tsunefumi Mizuno 23

Outer Galaxy quadrant (outer Galaxy) will be discussed. 銀河面拡散γ線: 宇宙線の空間分布

Perseus arm

Fermi_CR_2009Sep_GRBsymposium.ppt

Fermi Fermi-

• LAT View of

LAT View of the 3rd the 3rd Quadrant Quadrant

• One of the best studied regions in γ-rays

Vela, Geminga, Crab and Orion A/B

• Galactic plane between Vela and Geminga (green square) is ideal to study diffuse γ-rays

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

Vela Geminga Vela Crab Orion A/B

Tsunefumi Mizuno 24

Count Map (E>100 MeV)

Orion A/B

Fermi_CR_2009Sep_GRBsymposium.ppt

Construction of the Model Construction of the Model

• Fit gamma-ray data with a linear

combination of model maps p

I(E, l, b) = ΣA(E)*HI(l,b) + ΣB(E)*Wco(l,b) +Σothers+Σpoint_sources

• Coefficients give the gamma-ray (CR)

spectral distrib tion of o ter Gala spectral distribution of outer Galaxy 拡散γ線 = Σ ISM*宇宙線+α Local arm Local arm

Perseus arm

=

+ +

Tsunefumi Mizuno 25

+ others (ISM, IC and point sources)

Fermi_CR_2009Sep_GRBsymposium.ppt

HI Emissivity (CR) Spectra HI Emissivity (CR) Spectra

HI Emissivity Spectrum of each ring

(local arm) (interarm) (P ) (Perseus arm)

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

• 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

Tsunefumi Mizuno 26

• 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

Fermi_CR_2009Sep_GRBsymposium.ppt

Summary Summary

• 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 this finding + PAMELA positron fraction require local sources (astrophysical or exotic) nearby GRB is one of possible origins S t i till l b t t l t i d Source nature is still unclear but strongly constrained.

• CRs in distant locations can be “measured” by diffuse γ-rays.

EGRET G V t fi d

宇宙線電子：近傍の宇宙線源をとらえた？

EGRET GeV-excess not confirmed. Fermi proves that local CR nuclei spectra are close to those of LIS.

拡散γ線：銀河宇宙線の大局分布が明らかになりつつある

Tsunefumi Mizuno 27

CR density distribution in outer Galaxy is being studied.

Thank you for your attention!