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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt Diffuse Gamma Diffuse Gamma- use Ga use Ga a a Rays seen by Fermi Rays seen by Fermi Gamma Gamma-ray Space Gamma Gamma-ray Space ray Space ray Space Telescope Telescope Tsunefumi Tsunefumi Mizuno

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

Diffuse Gamma Diffuse Gamma- use Ga a use Ga a Rays seen by Fermi Rays seen by Fermi Gamma Gamma-ray Space ray Space Gamma Gamma-ray Space ray Space Telescope Telescope

Tsunefumi Tsunefumi Mizuno Mizuno Hiroshima Univ Hiroshima Univ Hiroshima Univ. Hiroshima Univ.

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

LAT Collaboration Collaboration

Tsunefumi Mizuno 1

27 March 2009, Tokyo, Japan 27 March 2009, Tokyo, Japan

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

Short History of Gamma Short History of Gamma-

  • ray Astronomy

ray Astronomy

  • Prediction of Gamma-rays

Feenberg & Primakoff (1948): inverse Compton scattering (photon & g ( ) p g (p CR electron) Hayakawa (1952): π0-decay (matter & CR nucleon) Hutchinson (1952): bremsstrahlung (matter & CR electron) Morrison (1958) Morrison (1958)

  • Early Observations

OSO-3 (1967-1968): First detection of gamma-rays from Gal. plane SAS-2 (1972-1973) map of the Gal plane ( ) COS-B (1975-1982) EGRET(1991-2000)

  • Diffuse gamma rays has been one of main topics of gamma ray

map of the Gal. plane study CR and matter distribution

  • Diffuse gamma-rays has been one of main topics of gamma-ray

astronomy since the beginning of its history

A powerful probe to study cosmic-rays (CRs) and the

Tsunefumi Mizuno 2

A powerful probe to study cosmic rays (CRs) and the interstellar medium/radiation field in the Milky Way

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

The Era of the Fermi Gamma The Era of the 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) 10 10 keV keV -

  • 25

25 MeV MeV GBM

sensitivity to point sources

  • Large Effective Area (>=8000 cm2

(launched on June 11, 2008)

  • Large Effective Area (>=8000 cm

in 1-10 GeV)

  • Good Angular Resolution

(3.5deg@100 MeV and 0.6 deg@1 GeV; 68% contaminant radii)

  • Large FOV (2.4 sr) and uniform

exposure

Tsunefumi Mizuno 3

Atwood et al. (arXiv:0902.1089) Ideal for the study of diffuse gamma-rays

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

The LAT 3 Month All The LAT 3 Month All-

  • Sky Map

Sky Map

  • The Fermi-LAT has already surpassed the EGRET in many aspects

More than 3 dozen pulsars (6 by EGRET) 205 bright sources and 444 above 5 σ (271 by EGRET) arXiv:0902.1340 exciting results on individual targets (CTA1, GRB080916C, etc.) e c t g esu ts o d dua ta gets (C , G 0809 6C, etc ) LAT all-sky E>200 MeV

Mid l tit d i

Tsunefumi Mizuno 4

Mid-latitude region (so-called GeV excess)

Understand CRs close to the solar system

Mid/High-latitude region (local CR flux and spectrum)

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

EGRET EGRET GeV GeV Excess Excess

  • EGRET observations showed

excess emission > 1 GeV everywhere in the sky when

|b|=6°-10°

everywhere in the sky when compared with cosmic-ray propagation models based on

0.1 1 10 GeV |b| 2° 6°

directly measured cosmic-ray nuclei and electron spectra

  • Variety of possible

|b|=2°-6°

y p explanations

Variations in cosmic-ray spectra over Galaxy

|b|<=2°

spectra over Galaxy Unresolved sources (pulsars, SNRs, …) Dark matter

Tsunefumi Mizuno 5

Dark matter Instrumental

Hunter et al. 1997 ~100% difference above 1 GeV

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

The Fermi LAT View The Fermi LAT View

|b|=10°-20° a

  • Spectra shown for mid-latitude range => GeV excess in this region of

th k i t fi d the sky is not confirmed.

  • Sources are not subtracted but are a minor component.
  • LAT errors are dominated by systematic uncertainties and are

currently estimated to be ~10% > this is preliminary currently estimated to be ~10% -> this is preliminary

  • Gamma-ray spectra can be explained by cosmic-ray propagation

model consistent with directly measured cosmic-ray nuclei and electron

Tsunefumi Mizuno 6

model consistent with directly measured cosmic ray nuclei and electron spectra.

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

Study of Local CRs using HI Study of Local CRs using HI

Observed Wco (Dame, et al. 2001)

Galactic Center (sigificant contribution from IC)

20° 0°

  • 20°

Galactic Longitude 180° 90° 0° 270° 180°

  • Want to decouple gamma-rays related to

the atomic gas from other components

l=200°-260° |b|=22°-60°

IC model map @ 1 GeV (Relative) 100

the atomic gas from other components

  • Study region away from the Galactic

center and the plane:

Small contribution from point sources, IC

c Longitude

100 10

Small contribution from point sources, IC and molecular hydrogen gas Most of HI gas is close to the solar system (<=1 kpc)

Galactic Longitude Galactic

1

Tsunefumi Mizuno 7

Measurement of HI emissivity spectrum constrains the local CR flux and the spectrum

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

Correlation with the HI Column Density Correlation with the HI Column Density

  • Mask point sources (1° radius) and subtract IC and residual point source contributions.
  • Correlation btw. γ-ray intensity and gas column density in 0.2-10 GeV. The slope gives

the γ-ray emissivity spectrum of local HI gas produced through interactions with CRs. 200-282 MeV 1.6-2.26 GeV ntensity E2 x γ-ray In

(error bars are statistical only)

6 4 9 05 G V 400 566 MeV

HI column density (1020 cm-2)

E

( y)

6.4-9.05 GeV 400-566 MeV

Tsunefumi Mizuno 8

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

Emissivity of Local Atomic Hydrogen Emissivity of Local Atomic Hydrogen

  • Gamma-ray emissivity spectrum per H-atom
  • Agree with the model prediction from the local interstellar spectrum

consistent with measurements at Earth

CR nucleon spectrum in the vicinity of the sloar system is close to that directly measured at Earth

(30% sys error is assumed below 1 GeV) (30% sys error is assumed below 1 GeV)

nucleon- l

Calibration below 200 MeV is underway and will allow us to discuss CR electron spectrum

nucleon electron- bremsstrahlung

Tsunefumi Mizuno 9

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

Summary Summary

  • Diffuse gamma-ray is a powerful probe to study cosmic-ray

spectrum and distribution

  • Fermi-LAT is a superb instrument for diffuse emission

studies

Large Aeff and good angular resolution uniform and deep coverage of the sky

  • First results on mid latitude Galactic emission show no

evidence for EGRET feature > 1 GeV seen in the same region

  • f the sky
  • Mid/high-latitude observation indicates the CR nucleon

spectrum in the vicinity of the solar system is close to that directly measured at Earth

Work to analyze and understand diffuse emission over the entire sky is in progress.

Tsunefumi Mizuno 10

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

And More to Come And More to Come

Contributions to ICRC 2009 (http://icrc2009.uni.lodz.pl/)

  • GeV-non-excess
  • Large-scale diffuse

Orion MC

  • Large-scale diffuse
  • The Galactic-Center
  • Extragalactic gamma-ray background
  • Orion/Monoceros molecular clouds

Orion/Monoceros molecular clouds

  • LMC
  • Diffuse gamma-rays from Cassiopeia region

?

Digel et al. 1999 G C

?

Mayer-Hasselwander et al. 1998 G.C.

Stay tuned for further results on diffuse

?

Tsunefumi Mizuno 11

Stay tuned for further results on diffuse gamma-ray emission by Fermi-LAT

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

Backup Slides Backup Slides Backup Slides Backup Slides

Tsunefumi Mizuno 12

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

EGRET, the Predecessor Instrument EGRET, the Predecessor Instrument

EGRET all-sky (galactic coordinates) E>100 MeV

  • 1991-2000, 30 MeV-30 GeV

resolved 271 gamma ray sources (Hartman et al 1999)

Tsunefumi Mizuno 13

resolved 271 gamma-ray sources (Hartman et al. 1999) detailed study of Galactic diffuse emission (Hunter et al. 1997) and extragalactic diffuse emission (Sreekumar et al. 1998)

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

EGRET EGRET GeV GeV Excess (2) Excess (2)

Above 1 GeV, EGRET data are above the GALPROP prediction GALPROP prediction everywhere in the sky LAT statistics are LAT statistics are already good enough to confirm/refute all- sky nature of this

Strong, Strong, Moskalenko Moskalenko & & Reimer Reimer ApJ ApJ 613 613, , 962 962 ( (2004 2004) )

Tsunefumi Mizuno 14

4a-f

sky nature of this excess

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SLIDE 15

Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

Gamma Gamma-

  • ray Count Maps

ray Count Maps

Count maps in E>=200 MeV, accumulated from Aug. 4 to Oct. 30

Count Map (South Region) Count Map (North Region) ( LAT t l iti )

  • The Fermi-LAT has already tripled the number of known gamma-ray

sources (29 by LAT three month catalog and 9 in EGRET 3rd catalog).

(green crosses: LAT catalog source positions)

Tsunefumi Mizuno 15

( y g g)

The diffuse spectrum by Fermi-LAT is less affected by unresolved sources than early missions.

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Fermi_Diffuse_ASJ_JPS_2009Mar.ppt

Column Density of Atomic Hydrogen Column Density of Atomic Hydrogen

Column density maps of HI gas (w/ optical depth correction)

N(HI) (South Region) N(HI) (North Region)

  • N(HI) is small, less than 18x1020 cm-2 throughout the region

Small uncertainty of the optical depth correction

  • We see a correlation between diffuse gamma-ray counts and N(HI)

Tsunefumi Mizuno 16

  • We see a correlation between diffuse gamma-ray counts and N(HI)