Fermi_Diffuse_2009Mar.ppt

Diffuseuse GaGamma
GammaaRays seen by Fermi
Fermi-LAT and CosmicCosmicRay Distributions
Tsunefumi Mizuno
Hiroshima Univ
Univ.
on behalf of the FermiFermi-LAT
Collaboration
18 March 20092009,, Ehime, Japan
Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

Short History of Gamma
Gamma--ray Astronomy• Prediction of Gamma-rays¾Feenberg
g & Primakoff ((1948):) inverse Compton
pscatteringg (photon(p&CR electron)¾Hayakawa (1952): π0-decay (matter & CR nucleon)¾Hutchinson (1952): bremsstrahlung (matter & CR electron)¾Morrison (1958)• Early Observations¾OSO-3 (1967-1968): First detection of gamma-rays from Gal. plane¾SAS-2 ((1972-1973))
map
p of the Gal. planep¾COS-B (1975-1982)
study CR and matter distribution• Diffuse gamma-rays has been one of main topics of gamma-ray
astronomytsinceitheth beginningb i i
off its
it history
hi tAppowerful probe
pto studyy cosmic-rays
y ((CRs))
and the interstellar medium
Tsunefumi Mizuno

2Fermi_Diffuse_2009Mar.ppt

EGRET, the Predecessor Instrument
EGRET all-sky (galactic coordinates) E>100 MeV• 1991-2000, 30 MeV-30 GeV¾resolved 271 gamma
gamma-ray
ray sources (Hartman et alal. 1999)¾detailed study of Galactic diffuse emission (Hunter et al. 1997) andextragalactic diffuse emission (Sreekumar et al. 1998)

Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

The LAT 3 Month AllAll-Sky Map
LAT all-sky E>200 MeV

Diffuse emission ~80% total gamma-ray
gamma ray flux

• The Fermi-LAT has already surpassed the EGRET in many aspects¾More than 3 dozen pulsars (6 by EGRET)¾205 bright sources and 444 above 5 σ (271 by EGRET) arXiv:0902.1340
arXiv:0902 1340
¾exciting results on individual targets
CTA1, GRB080916C, Vela Pulsar, etc.
Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

Performance of the Fermi LAT•

Primary observing mode is Sky
sensitivity to point sources
Survey– Full sky every 2 orbits (3hhours))– Uniform exposure, with eachregion viewed for ~30 minutes
everyy 2 orbits– Best serves majority ofscience, facilitates
multiwavelength observation
planning– Exposure intervals
Atwood et al.
commensurate with typical(arXiv:0902.1089)
instrument integration times
for sources• Large Field of View (2.4 sr)– EGRET sensitivity reached in • Large Effective Area (>=8000 cm2 in 1-10 GeV)
days
• Good Angular Resolution (3.5deg@100 MeV
and 0.6deg@1 GeV; 68% contaminant radii, bestevent class)Large FOV and uniform exposure: ideal for the study of diffuse gamma-rays
Tsunefumi Mizuno

5Plan of this Talk

1.
2.
3
3.
4.
Tsunefumi Mizuno

Fermi_Diffuse_2009Mar.ppt

Models to study diffuse gamma-rays
Mid-latitude region (GeV-excess)Mid/high latitude region (local CR flux and spectrum)
Mid/high-latitude
LMC (local group galaxy)6Fermi_Diffuse_2009Mar.ppt

Models to Study Diffuse
Gamma-rays:
GammaCR Propagation,
p g, Maps
p of Gas
and ISRF

Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

CR Interactions with the Interstellar Medium
SNR RX J1713J1713-3946
42 sigma (2003+2004 data)

ISMX,γ+e-Moskalenko 2005

BP diffusion
He energy
gy losses
CNO
reacceleration+convection e etc. π +-gas

π0Fermigas_PeICISRF+π- p+-LiBeB

HeCNO

FluxPSF

HESS
Preliminary

Chandra20 GeV/nBESSPAMELA

Tsunefumi Mizuno

AMS

helio-modulation

ACE

CR species:¾ Only 1 location¾ modulation

We need models of CR injection, CR propagation, ISRF,
gas distribution and gamma-ray production

8Fermi_Diffuse_2009Mar.ppt

CR Injection/Propagation by GALPROP
SNR distribution•The cosmic-rays have to be accelerated¾What are the accelerator?
9SNR pulsars
9SNR,pulsars, … ?
9Affects the spatial distribution
and spectra•Propagation through the galaxy¾Diffusion coefficients, secondaryproduction, energy losses, …
09Determined from local observations ofcosmic rays
cosmic-rays

0.1

1Tsunefumi Mizuno

10(Case & Bhattacharya 1998)
Pulsar distribution(Lorimer 2004)
CR distribution from γ-rays(Strong & Mattox 1996)

51015 kpc

100 GeV

Strong, Moskalenko & Reimter, 2004

9Model Gas Maps

Fermi_Diffuse_2009Mar.ppt• Gas distribution determined from radio surveys¾velocity => distance through a rotation curve
HI density from LAB survey¾Opacity correction needed especially close to Gal
Gal. plane

G.C.

Clements(1985)(R0,v0)=(8.5 kpc, 220 km/s)

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

30°
30Dame et al. 2001

0°
-30°

H2 density from 2
2.66 mm CO line
¾assumptions on Xco=N(H2)/WCO

Tsunefumi
Mizunotargetfor producing gamma-rays through π0-decay and electron bremsstrahlung 10

Fermi_Diffuse_2009Mar.ppt

InternterS
Stellar Radiation Field•CR e+/e- need targets to create g-rays¾Interstellar radiation field determined from a realistic model
taking into account stellar and dust distribution
9Starlight (~ 0.1 μm – 10 μm)
9Dust (~ 10 μm – 300 μm)
ISRF energy density
9CMB (>300 μm)

There are systematic
uncertainties
associated with gas
and ISRF!

R=0 kpc
R=4 kpc
R=8 kpc
R=12 kpc

StellarDust

CMB

Porter et al. 2008
Tsunefumi Mizuno

11Fermi_Diffuse_2009Mar.ppt

Fermi--LAT Diffuse Analysis
Fermi
Distribution of ISM
HI/CO surveys, ISRF model+ spatial mapping of ISM+ conversion to HI/H2 column density

Galactic gamma-ray emissivities• from GALPROP cosmic-ray
propagation• derived from data for special regions

Line-of-sight integration (by GALPROP) to create gamma-ray
flux map for indivicualICEBπ0• emission processes• ISM componentst• galactocentric annuli

γ-ray model map has been used for point source and diffuse analyses• already provided lots of exciting results on individual targets• possible uncertainties (or improvement)

Tsunefumi Mizuno¾CR source distrubution, CR propagation¾optical depth correction (HI), Xco (H2), ISRF
¾dark gas (Grenier et al. 2005)

Deviations from input model
used to iteratively improve thediffuse model
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Fermi_Diffuse_2009Mar.ppt

Mid--Latitude Region (|Mid(|bb|=10|=10°°-20°20°):
GeV Excess?

Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

EGRET GeV Excess (1)•EGRET observations showedexcess emission > 1 GeV
when compared with cosmicray propagation models
based on local cosmic-ray
nuclei and electron spectra•Variety of possible
explanationslti¾Variations in cosmic-ray
spectra over Galaxy¾Unresolved sources(pulsars, SNRs, …)¾Dark matter¾Instrumental
Tsunefumi Mizuno|b|=6°-10°

0.1

110 GeV|b| 2° 6°|b|=2°-6°|b|<=2°~100% difference above 1 GeV
Hunter et al. 1997

14Fermi_Diffuse_2009Mar.ppt

EGRET GeV Excess (2)Above 1 GeV, EGRET
data are above theGALPROP prediction
everywhere in thesky

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

Tsunefumi Mizuno

LAT statistics arealready good enoughto confirm/refute allsky nature of this4a-fexcess
15Fermi_Diffuse_2009Mar.ppt

The Fermi LAT View (1)|b|=10°-20°

Galprop conventional• Spectra shown for mid-latitude range => GeV excess in thisregion
i off theth sky
k isi nott confirmed.
fid• 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• EGRET data is prepared as in Strong, et al. 2004 with a 15%
systematic error assumed to dominate (Esposito, et al. 1999)• EG+instrumental is assumed to be isotropic and determinedfrom fitting the data at at |b| > 10°.
Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

Fermi--LAT View (2)Fermi• Intermediate latitude gamma-ray spectra can be

explained by cosmic-ray propagation model consistent
with locally measured cosmic-ray nuclei and electronspectra. The EGRET GeV excess is not seen in thisregion of the sky (|b|=10°-20°)(|b| 10 20 ) with the LAT.
• LAT spectrum of Vela (Abdo et al. arXiv:0812.2960)
also confirms that the EGRET GeV excess isinstrumental.
• Work to analyze and understand diffuse emission
over the entire sky is in progress.

Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

Mid/HighMid/Highg -Latitude Region
g(|b(|b|=22|=22°°-60°60° in Third Quadrant):
Quadrant):
Local CR Flux and the Spectrum

Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

Study of Local CRs using HI
Observed Wco(Dame, et al. 2001)

Galactic Center(sigificant contribution from IC)

20°
00°
-20°

90°0°
Galactic Longitude• AwayA
ffrom ththe G
Galacticl ti CenterC t andd theth Plane:
Pl¾Small contribution from IC and point sources¾Less affected by H2 (uncertainty of Wco)
¾Small optical depth correction¾M t off HI gas iis close¾Mostltot solarl systemt270°

l=200°-260° 180°|b|=22°-60°

IC model map @ 1 GeV (Relative)
Galacticc Longitude

180°

100

101
Galactic Longitude

Measurement of HI emissivity constrains the local CR
flux and the spectrum
Tsunefumi Mizuno
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Fermi_Diffuse_2009Mar.ppt

Gamma--ray Count Maps
Gamma

Count maps in E>=200 MeV, accumulated from Aug. 4 to Oct. 30
Count Map (South Region)

Count Map (North Region)• 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).
¾The diffuse spectrum by Fermi-LAT is less affected by unresolved
sources than early missions.
Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

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 region¾Small uncertainty of the optical depth correction• We see a correlation between diffuse gamma-ray counts and N(HI)
Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

Correlation with the HI Column Density

E2 x γ-ray Intensity•Point sources are masked (1° radius). IC and residual point source contributions aresubtracted.
•Correlation from 200 MeV to 10 GeV. The slope gives the γ-ray emissivity of HI gas.
200-282 MeV

1.6-2.26 GeV

HI column density (1020 cm-2)

400-566 MeV

Tsunefumi Mizuno

6.4-9.05 GeV

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Fermi_Diffuse_2009Mar.ppt

Emissivity of Local Atomic Hydrogen•Similar to previous works but with much better statistics especially above 1 GeV.
•Agree with the model prediction from the local interstellar spectrum consistent withmeasurements at Earth.

Local CR nucleon spectrum is close to that directly measured at Earth
Emissivity by Fermi-LAT(30% sys error isassumed below 1 GeV)

Calibration below 200 MeV isunderway
dandd will
ill allowll
us totdiscuss CR electron spectrum

EGRET (Digel(Di l ett al.
l 2001)

nucleonnucleon
electronbremsstrahlung

102

Tsunefumi Mizuno(assumed electron spectra differ below a few 100s MeV)

103 MeV

104
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Fermi_Diffuse_2009Mar.ppt

Large Magellanic Cloud(Local Group Galaxy)

Tsunefumi Mizuno

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Local Group Galaxies

Fermi_Diffuse_2009Mar.ppt

EGRET Observation Summary:• LMC detection: CR density is similar to MW• SMC non-detection: CR density is smaller than in the MW• FirstFi t direct
dit evidence:
idCRs
CR are galacticl ti andd nott universalil• M31 non-detection: has to have smaller CR density than the MW((size M31>MW))

Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

Why Study the Large Magellanic Clouds?
LMC is• seen ~ face-on (i ≈ 27°)
• nearby (~ 50 kpc)
• active (many massive starforming regions)

30 Doradus

NASA/JPL-Caltech/M. Meixner (STScI) & the SAGE Legacy Team
Tsunefumi Mizuno

ATCA+Parkes H I (Kim et al. 2003)
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Fermi_Diffuse_2009Mar.ppt

EGRET View of the LMC
EGRET maps and profiles of LMC

Sreekumar et al. (1992)

EGRET achievements
LMC

Tsunefumi Mizuno• first detection of LMC• morphology consistent with radio data(yet no real spatial resolution of theemission)• flux >100 MeV: (1(1.99 ± 0.4)
0 4) 10-7 ph cm-2 s-1• flux consistent with either:- dynamic balance model- uniform CR density equal to that in solar
neighborhood

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Fermi_Diffuse_2009Mar.ppt

EGRET vs. FermiFermi-LAT View of LMC

LMC

adaptively smoothed counts map (s.n.r. = 5)
Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

Fermi--LAT Image of the LMC
Fermi

CRATES J060106-703606

30 Doradus

Dust map (SFD)

161 days of survey data
~ 1300 events above 100 MeVLocation (assuming point source):a = 84.6 ± 0.2 (95%)
d = -69.1 ± 0.1 (95%)
Consistent with 30 Doradus / R136
location (a=84.67, d=-69.10)

adaptively
smoothed 100 MeV - 10 GeV counts map (s.n.r. = 5)
Tsunefumi Mizuno

29Summary

Fermi_Diffuse_2009Mar.ppt• Fermi-LAT is a superb instrument for diffuse emission
studies¾uniform and deep
p coverageg of the skyy• CR propagation model and gas/ISRF maps have beendeveloped¾already provided many exciting results of individual sources• First
st results
esu ts oon midd latitude
at tude Ga
Galacticact c eemission
ss o sshowo noo
evidence for EGRET feature > 1 GeV seen in the same
region of the sky• Mid-highMid high latitude observation indicates the local CR
nucleon spectrum is close to that measured at Earth• Easily detected diffuse emission from LMC¾Emission resolved => 30-Doradus, host galaxy¾More results very soon
Tsunefumi Mizuno

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Fermi_Diffuse_2009Mar.ppt

And More to Come
Contributions to ICRC 2009 (http://icrc2009.uni.lodz.pl/)• GeV-non-excessOrion MC• Large-scale diffuse• The Galactic-Center• Extragalactic gamma-ray background• Orion/Monoceros molecular clouds• LMC• Diffuse gamma-rays from Cassiopeia region
GCG.C.
Mayer-Hasselwander
et al. 1998

Digel et al. 1999?

?

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

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