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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 Mizuno Hiroshima Univ Hiroshima Univ Hiroshima Univ. Hiroshima Univ. on behalf of the Fermi on behalf of the Fermi- -LAT LAT Collaboration Collaboration 27 March 2009, Tokyo, Japan 27 March 2009, Tokyo, Japan Tsunefumi Mizuno 1

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): π 0 -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 map of the Gal plane � COS-B (1975-1982) study CR and matter distribution � EGRET(1991-2000) • Diffuse gamma rays has been one of main topics of gamma ray • 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 A powerful probe to study cosmic rays (CRs) and the interstellar medium/radiation field in the Milky Way Tsunefumi Mizuno 2

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 • Gamma Gamma- -ray Burst Monitor (GBM) ray Burst Monitor (GBM) 10 keV 10 keV - - 25 25 MeV MeV GBM GBM (launched on June 11, 2008) sensitivity to point sources • Large Effective Area (>=8000 cm 2 • 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 Ideal for the study of diffuse gamma-rays Atwood et al. (arXiv:0902.1089) Tsunefumi Mizuno 3

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 Mid-latitude region i Mid/High-latitude region (so-called GeV excess) (local CR flux and spectrum) Understand CRs close to the solar system Tsunefumi Mizuno 4

Fermi_Diffuse_ASJ_JPS_2009Mar.ppt EGRET EGRET GeV GeV Excess Excess • EGRET observations showed | b |=6 ° -10 ° excess emission > 1 GeV everywhere in the sky when everywhere in the sky when compared with cosmic-ray 0.1 1 10 GeV propagation models based on | b |=2 ° -6 ° | b | 2 ° 6 ° directly measured cosmic-ray nuclei and electron spectra • Variety of possible y p explanations � Variations in cosmic-ray | b |<=2 ° spectra over Galaxy spectra over Galaxy � Unresolved sources (pulsars, SNRs, …) � Dark matter � Dark matter ~100% difference above 1 GeV � Instrumental Hunter et al. 1997 Tsunefumi Mizuno 5

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 the sky is not confirmed. th k i t fi d • 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 model consistent with directly measured cosmic ray nuclei and electron spectra. Tsunefumi Mizuno 6

Fermi_Diffuse_ASJ_JPS_2009Mar.ppt Study of Local CRs using HI Study of Local CRs using HI Galactic Center Observed Wco (sigificant contribution from IC) (Dame, et al. 2001) 20 ° 0 0 ° -20 ° 180 ° 90 ° 0 ° 270 ° 180 ° l =200°-260° Galactic Longitude | b |=22°-60° • Want to decouple gamma-rays related to IC model map @ 1 GeV (Relative) the atomic gas from other components the atomic gas from other components 100 100 c Longitude • Study region away from the Galactic center and the plane: 10 � Small contribution from point sources, IC � Small contribution from point sources, IC Galactic and molecular hydrogen gas � Most of HI gas is close to the solar 1 system (<=1 kpc) Galactic Longitude Measurement of HI emissivity spectrum constrains the local CR flux and the spectrum Tsunefumi Mizuno 7

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. ntensity 1.6-2.26 GeV 200-282 MeV E 2 x γ -ray In ( (error bars are statistical only) y) E HI column density (10 20 cm -2 ) 400 566 MeV 400-566 MeV 6 4 9 05 G V 6.4-9.05 GeV Tsunefumi Mizuno 8

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) Calibration below 200 MeV is underway and will allow us to nucleon- discuss CR electron spectrum nucleon l electron- bremsstrahlung Tsunefumi Mizuno 9

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 of 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

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 Orion MC • Large-scale diffuse • Large-scale diffuse • The Galactic-Center • Extragalactic gamma-ray background • Orion/Monoceros molecular clouds Orion/Monoceros molecular clouds Digel et al. 1999 • LMC • Diffuse gamma-rays from Cassiopeia region ? G C G.C. Mayer-Hasselwander ? ? et al. 1998 Stay tuned for further results on diffuse Stay tuned for further results on diffuse gamma-ray emission by Fermi-LAT Tsunefumi Mizuno 11

Fermi_Diffuse_ASJ_JPS_2009Mar.ppt Backup Slides Backup Slides Backup Slides Backup Slides Tsunefumi Mizuno 12

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) � 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) Tsunefumi Mizuno 13

Fermi_Diffuse_ASJ_JPS_2009Mar.ppt EGRET GeV EGRET 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 Strong, Strong, Moskalenko Moskalenko & & Reimer Reimer ApJ ApJ 613 613, , 962 962 ( (2004 2004) ) to confirm/refute all- sky nature of this sky nature of this 4a-f excess Tsunefumi Mizuno 14

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 (North Region) Count Map (South Region) (green crosses: LAT catalog source positions) ( 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 3 rd catalog). ( y g g) � The diffuse spectrum by Fermi-LAT is less affected by unresolved sources than early missions. Tsunefumi Mizuno 15

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) (North Region) N(HI) (South Region) • N(HI) is small, less than 18x10 20 cm -2 throughout the region � Small uncertainty of the optical depth correction • We see a correlation between diffuse gamma-ray counts and N(HI) • We see a correlation between diffuse gamma-ray counts and N(HI) Tsunefumi Mizuno 16